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Mastocytosis is a heterogeneous disease characterized by an abnormal accumulation of mast cells (MCs) in 1 or several organs. Although a somatic KIT D816V mutation is detected in ∼85% of patients, attempts to demonstrate its oncogenic effect alone have repeatedly failed, suggesting that additional pathways are involved in MC transformation. From 3 children presenting with both Greig cephalopolysyndactyly syndrome (GCPS, Mendelian Inheritance in Man [175700]) and congenital mastocytosis, we demonstrated the involvement of the hedgehog (Hh) pathway in mastocytosis. GCPS is an extremely rare syndrome resulting from haploinsufficiency of GLI3, the major repressor of Hh family members. From these familial cases of mastocytosis, we demonstrate that the Hh pathway is barely active in normal primary MCs and is overactive in neoplastic MCs. GLI3 and KIT mutations had a synergistic, tumorigenic effect on the onset of mastocytosis in a GCPS mouse model. Finally, Hh inhibitors suppressed neoplastic MC proliferation in vitro and extend the survival time of mice with aggressive systemic mastocytosis (ASM). This work revealed, for the first time, the involvement of Hh signaling in the pathophysiology of mastocytosis and demonstrated the cooperative effects of the KIT and Hh oncogenic pathways in mice with ASM, leading to the identification of new promising therapeutic targets.

Low-density lipoprotein (LDL) receptor-related protein-associated protein 1 (LRPAP1) had been identified by B-cell receptor (BCR) expression cloning and subsequent protein array screening as a frequent and proliferation-inducing autoantigen of mantle cell lymphoma (MCL). Of interest, high-titered and light chain–restricted LRPAP1 autoantibodies were detected in 8 of 28 patients with MCL. In the present study, LRPAP1 autoantibodies in sera of patients treated within the Younger and Elderly trials of the European MCL Network were analyzed regarding frequency, association with disease characteristics, and prognostic impact. LRPAP1 autoantibodies were detected in 41 (13%) of 312 evaluable patients with MCL. These LRPAP1 autoantibodies belonged predominantly to the immunoglobulin G (IgG) class and were clonally light chain restricted (27 with κ light chains, 14 patients with λ light chains). Titers ranged between 1:400 and 1:3200. The presence of LRPAP1 autoantibodies was not significantly associated with any baseline clinical characteristic, however, it was associated with a superior 5-year probability for failure-free survival (FFS) of 70% (95% confidence interval [CI], 57% to 87%) vs 51% (95% CI, 44% to 58%), P = .0052; and for overall survival (OS) of 93% (95% CI, 85% to 100%) vs 68% (95% CI, 62% to 74%), P = .0142. LRPAP1-seropositive patients had a Mantle Cell Lymphoma International Prognostic Index–adjusted hazard ratio for FFS of 0.48 (95% CI 0.27-0.83, P = .0083) and for OS of 0.47 (95% CI 0.24-0.94, P = .032). LRPAP1 autoantibodies were frequently detected in a large cohort of MCL patients treated within prospective multicenter clinical trials. Our results suggest better outcomes for LRPAP1-autoantibody seropositive patients.

With the introduction of large-scale molecular profiling methods and high-throughput sequencing technologies, the genomic features of most lymphoid neoplasms have been characterized at an unprecedented scale. Although the principles for the classification and diagnosis of these disorders, founded on a multidimensional definition of disease entities, have been consolidated over the past 25 years, novel genomic data have markedly enhanced our understanding of lymphomagenesis and enriched the description of disease entities at the molecular level. Yet, the current diagnosis of lymphoid tumors is largely based on morphological assessment and immunophenotyping, with only few entities being defined by genomic criteria. This paper, which accompanies the International Consensus Classification of mature lymphoid neoplasms, will address how established assays and newly developed technologies for molecular testing already complement clinical diagnoses and provide a novel lens on disease classification. More specifically, their contributions to diagnosis refinement, risk stratification, and therapy prediction will be considered for the main categories of lymphoid neoplasms. The potential of whole-genome sequencing, circulating tumor DNA analyses, single-cell analyses, and epigenetic profiling will be discussed because these will likely become important future tools for implementing precision medicine approaches in clinical decision making for patients with lymphoid malignancies.

Allogeneic hematopoietic stem cell transplantation (alloSCT) is curative for severe inborn errors of immunity (IEIs), with recent data suggesting alloSCT in adulthood is safe and effective in selected patients. However, questions remain regarding the indications for and optimal timing of transplant. We retrospectively compared outcomes of transplanted vs matched nontransplanted adults with severe IEIs. Seventy-nine patients (aged ≥ 15 years) underwent alloSCT between 2008 and 2018 for IEIs such as chronic granulomatous disease (n = 20) and various combined immune deficiencies (n = 59). A cohort of nontransplanted patients from the French Centre de Référence Déficits Immunitaires Héréditaires registry was identified blindly for case-control analysis, with ≤3 matched controls per index patient, without replacement. The nontransplanted patients were matched for birth decade, age at last review greater than index patient age at alloSCT, chronic granulomatous disease or combined immune deficiencies, and autoimmune/lymphoproliferative complications. A total of 281 patients were included (79 transplanted, 202 nontransplanted). Median age at transplant was 21 years. Transplant indications were mainly lymphoproliferative disease (n = 23) or colitis (n = 15). Median follow-up was 4.8 years (interquartile range, 2.5-7.2). One-year transplant-related mortality rate was 13%. Estimated disease-free survival at 5 years was higher in transplanted patients (58% vs 33%; P = .007). Nontransplanted patients had an ongoing risk of severe events, with an increased mean cumulative number of recurrent events compared with transplanted patients. Sensitivity analyses removing patients with common variable immune deficiency and their matched transplanted patients confirm these results. AlloSCT prevents progressive morbidity associated with IEIs in adults, which may outweigh the negative impact of transplant-related mortality.

Friedreich ataxia (FRDA) is a frequent autosomal recessive disease caused by a GAA repeat expansion in the FXN gene encoding frataxin, a mitochondrial protein involved in iron-sulfur cluster (ISC) biogenesis. Resulting frataxin deficiency affects ISC-containing proteins and causes iron to accumulate in the brain and heart of FRDA patients. Here we report on abnormal cellular iron homeostasis in FRDA fibroblasts inducing a massive iron overload in cytosol and mitochondria. We observe membrane transferrin receptor 1 (TfR1) accumulation, increased TfR1 endocytosis, and delayed Tf recycling, ascribing this to impaired TfR1 palmitoylation. Frataxin deficiency is shown to reduce coenzyme A (CoA) availability for TfR1 palmitoylation. Finally, we demonstrate that artesunate, CoA, and dichloroacetate improve TfR1 palmitoylation and decrease iron overload, paving the road for evidence-based therapeutic strategies at the actionable level of TfR1 palmitoylation in FRDA.

The role of ribosome biogenesis in erythroid development is supported by the recognition of erythroid defects in ribosomopathies in both Diamond-Blackfan anemia and 5q− syndrome. Whether ribosome biogenesis exerts a regulatory function on normal erythroid development is still unknown. In the present study, a detailed characterization of ribosome biogenesis dynamics during human and murine erythropoiesis showed that ribosome biogenesis is abruptly interrupted by the decline in ribosomal DNA transcription and the collapse of ribosomal protein neosynthesis. Its premature arrest by the RNA Pol I inhibitor CX-5461 targeted the proliferation of immature erythroblasts. p53 was activated spontaneously or in response to CX-5461, concomitant to ribosome biogenesis arrest, and drove a transcriptional program in which genes involved in cell cycle–arrested, negative regulation of apoptosis, and DNA damage response were upregulated. RNA Pol I transcriptional stress resulted in nucleolar disruption and activation of the ATR-CHK1-p53 pathway. Our results imply that the timing of ribosome biogenesis extinction and p53 activation is crucial for erythroid development. In ribosomopathies in which ribosome availability is altered by unbalanced production of ribosomal proteins, the threshold downregulation of ribosome biogenesis could be prematurely reached and, together with pathological p53 activation, prevents a normal expansion of erythroid progenitors.

Adult T-cell leukemia (ATL) is a lymphoid neoplasm caused by human T-cell leukemia virus type 1 (HTLV-1), which encodes the transcriptional activator Tax, which participates in the immortalization of infected T cells. ATL is classified into 4 subtypes: smoldering, chronic, acute, and lymphoma. We determined whether natural killer receptors (NKRs) were expressed in ATL. NKR expression (KIR2DL1/2DS1, KIR2DL2/2DL3/2DS2, KIR3DL2, NKG2A, NKG2C, and NKp46) was assessed in a discovery cohort of 21 ATL, and KIR3DL2 was then assessed in 71 patients with ATL. KIR3DL2 was the only NKR among those studied frequently expressed by acute-type vs lymphoma- and chronic/smoldering-type ATL (36 of 40, 4 of 16, and 1 of 15, respectively; P = .001), although acute- and lymphoma-type ATL had similar mutation profiles by targeted exome sequencing. The correlation of KIR3DL2 expression with promoter demethylation was determined by microarray-based DNA methylation profiling. To explore the role of HTLV-1, KIR3DL2 and TAX messenger RNA (mRNA) expression levels were assessed by PrimeFlow RNA in primary ATL and in CD4+ T cells infected with HTLV-1 in vitro. TAX mRNA and KIR3DL2 protein expressions were correlated on ATL cells. HTLV-1 infection triggered KIR3DL2 by CD4+ cells but Tax alone did not induce KIR3DL2 expression. Ex vivo, autologous, antibody-dependent cell cytotoxicity using lacutamab, a first-in-class anti-KIR3DL2 humanized antibody, selectively killed KIR3DL2+ primary ATL cells ex vivo. To conclude, KIR3DL2 expression is associated with acute-type ATL. Transcription of KIR3DL2 may be triggered by HTLV-1 infection and correlates with hypomethylation of the promoter. The benefit of targeting KIR3DL2 with lacutamab is being further explored in a randomized phase 2 study in peripheral T-cell lymphoma, including ATL (registered on https://clinicaltrials.gov as #NCT04984837).

The rare PEL-negative phenotype is one of the last blood groups with an unknown genetic basis. By combining whole-exome sequencing and comparative global proteomic investigations, we found a large deletion in the ABCC4/MRP4 gene encoding an ATP-binding cassette (ABC) transporter in PEL-negative individuals. The loss of PEL expression on ABCC4-CRISPR-Cas9 K562 cells and its overexpression in ABCC4-transfected cells provided evidence that ABCC4 is the gene underlying the PEL blood group antigen. Although ABCC4 is an important cyclic nucleotide exporter, red blood cells from ABCC4null/PEL-negative individuals exhibited a normal guanosine 3′,5′-cyclic monophosphate level, suggesting a compensatory mechanism by other erythroid ABC transporters. Interestingly, PEL-negative individuals showed an impaired platelet aggregation, confirming a role for ABCC4 in platelet function. Finally, we showed that loss-of-function mutations in the ABCC4 gene, associated with leukemia outcome, altered the expression of the PEL antigen. In addition to ABCC4 genotyping, PEL phenotyping could open a new way toward drug dose adjustment for leukemia treatment.

There is a Blood Commentary on this article in this issue., Key Points As a proof of concept, COVID-19 convalescent plasma represents an interesting approach in B-cell–depleted patients with protracted COVID-19.COVID-19 convalescent plasma induces a decrease in temperature and inflammatory parameters within 1 week associated with oxygen weaning., Anti-CD20 monoclonal antibodies are widely used for the treatment of hematological malignancies or autoimmune disease but may be responsible for a secondary humoral deficiency. In the context of COVID-19 infection, this may prevent the elicitation of a specific SARS-CoV-2 antibody response. We report a series of 17 consecutive patients with profound B-cell lymphopenia and prolonged COVID-19 symptoms, negative immunoglobulin G (IgG)-IgM SARS-CoV-2 serology, and positive RNAemia measured by digital polymerase chain reaction who were treated with 4 units of COVID-19 convalescent plasma. Within 48 hours of transfusion, all but 1 patient experienced an improvement of clinical symptoms. The inflammatory syndrome abated within a week. Only 1 patient who needed mechanical ventilation for severe COVID-19 disease died of bacterial pneumonia. SARS-CoV-2 RNAemia decreased to below the sensitivity threshold in all 9 evaluated patients. In 3 patients, virus-specific T-cell responses were analyzed using T-cell enzyme-linked immunospot assay before convalescent plasma transfusion. All showed a maintained SARS-CoV-2 T-cell response and poor cross-response to other coronaviruses. No adverse event was reported. Convalescent plasma with anti–SARS-CoV-2 antibodies appears to be a very promising approach in the context of protracted COVID-19 symptoms in patients unable to mount a specific humoral response to SARS-CoV-2., Visual Abstract

Anemia of inflammation, also known as anemia of chronic disease, is refractory to erythropoietin (EPO) treatment, but the mechanisms underlying the EPO refractory state are unclear. Here, we demonstrate that high mobility group box-1 protein (HMGB1), a damage-associated molecular pattern molecule recently implicated in anemia development during sepsis, leads to reduced expansion and increased death of EPO-sensitive erythroid precursors in human models of erythropoiesis. HMGB1 significantly attenuates EPO-mediated phosphorylation of the Janus kinase 2/STAT5 and mTOR signaling pathways. Genetic ablation of receptor for advanced glycation end products, the only known HMGB1 receptor expressed by erythroid precursors, does not rescue the deleterious effects of HMGB1 on EPO signaling, either in human or murine precursors. Furthermore, surface plasmon resonance studies highlight the ability of HMGB1 to interfere with the binding between EPO and the EPOR. Administration of a monoclonal anti-HMGB1 antibody after sepsis onset in mice partially restores EPO signaling in vivo. Thus, HMGB1-mediated restriction of EPO signaling contributes to the chronic phase of anemia of inflammation.

This is a related article to: Nucleoside ENTry modulates erythropoiesis (cf ci-dessous); International audience; Abstract The tight regulation of intracellular nucleotides is critical for the self-renewal and lineage specification of hematopoietic stem cells (HSCs). Nucleosides are major metabolite precursors for nucleotide biosynthesis and their availability in HSCs is dependent on their transport through specific membrane transporters. However, the role of nucleoside transporters in the differentiation of HSCs to the erythroid lineage and in red cell biology remains to be fully defined. Here, we show that the absence of the equilibrative nucleoside transporter (ENT1) in human red blood cells with a rare Augustine-null blood type is associated with macrocytosis, anisopoikilocytosis, an abnormal nucleotide metabolome, and deregulated protein phosphorylation. A specific role for ENT1 in human erythropoiesis was demonstrated by a defective erythropoiesis of human CD34+ progenitors following short hairpin RNA-mediated knockdown of ENT1. Furthermore, genetic deletion of ENT1 in mice was associated with reduced erythroid progenitors in the bone marrow, anemia, and macrocytosis. Mechanistically, we found that ENT1-mediated adenosine transport is critical for cyclic adenosine monophosphate homeostasis and the regulation of erythroid transcription factors. Notably, genetic investigation of 2 ENT1null individuals demonstrated a compensation by a loss-of-function variant in the ABCC4 cyclic nucleotide exporter. Indeed, pharmacological inhibition of ABCC4 in Ent1−/− mice rescued erythropoiesis. Overall, our results highlight the importance of ENT1-mediated nucleotide metabolism in erythropoiesis.

International audience; Scleromyxedema is a rare skin and systemic mucinosis that is usually associated with monoclonal gammopathy (MG). In this French, multicenter, retrospective study of 33 patients, we investigated the clinical and therapeutic features of MG-associated scleromyxedema. Skin molecular signatures were analyzed using a transcriptomic approach. Skin symptoms included papular eruptions (100%), sclerodermoid features (91%), and leonine facies (39%). MG involved an IgG isotype in all patients, with a predominant λ light chain (73%). Associated hematologic malignancies were diagnosed in 4/33 patients (12%) (smoldering myeloma, n=2; chronic lymphoid leukemia, n=1; and refractory cytopenia with multilineage dysplasia n=1). Carpal tunnel syndrome (33%), arthralgia (25%) and dermato-neuro syndrome (DNS) (18%) were the most common systemic complications. One patient with mucinous cardiopathy died of acute heart failure. Intravenous immunoglobulin (HDIVig) treatment alone or in combination with steroids appeared to be quite effective in nonsevere cases (clinical complete response achieved in 13/31 patients). Plasma cell-directed therapies using lenalidomide and/or bortezomib with dexamethasone and HDIVig led to a significant improvement in severe cases (HDIVig-refractory or cases with central nervous system or cardiac involvement). The emergency treatment of DNS with combined plasmapheresis, HDIVig, and high-dose corticosteroids induced the complete remission of neurological symptoms in 4/5 patients. Quantitative reverse transcriptase-PCR (RT-PCR) analysis of 6 scleromyxedema skin samples showed significantly higher profibrotic pathway levels (transforming growth factor β (TGFβ) and collagen-1) than in healthy skin. Prospective studies targeting plasma cell clones and/or fibrotic pathways are warranted for long-term scleromyxedema management.

Currently, prediction of time to treatment failure (TTF) and overall survival (OS) in mantle cell lymphoma (MCL) is based on the clinical factors included in the Mantle Cell Lymphoma International Prognostic Index (MIPI), and proliferation is assessed by Ki67. However, TP53 and SOX11 immunohistochemistry might improve risk stratification. We performed SOX11 and TP53 immunohistochemistry on the so far largest published cohort of lymphoma specimens (n = 365). All patients were treated in prospective trials of the European MCL Network. In multivariate analyses, including MIPI and Ki67, SOX11 expression was not associated with TTF, but patients with low SOX11 expression had shorter OS. On the contrary, high TP53 expression was a strong predictor of TTF and inferior OS compared with low TP53 expression in univariate and multivariate analyses adjusting for MIPI score and Ki-67 index (hazard ratio [HR], 2.0; P = .0054 for TTF, and HR, 2.1; P = .068 for OS). In particular, patients with high TP53 expression (>50% positive lymphoma cells) had a shorter TTF and poor OS independent of both MIPI score and Ki-67 index. Thus, TP53 immunohistochemistry is a suitable test for routine diagnostic practice to assess MCL prognosis.

On Behalf of the European Mantle Cell Lymphoma Network Background: Mantle cell lymphoma (MCL) was usually characterized by a poor long term outcome. Starting in 2004, the European MCL Network has performed the randomized phase 3 MCL Younger trial for first-line treatment of patients with MCL in Ann-Arbor stage II-IV, aged < 66 years and suitable for autologous stem cell transplantation (Hermine et al., Lancet 2016). In this protocol, efficacy and safety of an alternating R-CHOP/R-DHAP induction followed by an ARA-C containing high dose consolidation with autologous blood stem cell transplantation (ASCT) was compared to R-CHOP followed by myeloablative radio-chemotherapy and ASCT. In the initial analysis, the primary outcome time to treatment failure (TTF) was significantly prolonged in the ARA-C arm (5 years rate 65% vs 40%; p=0.038). Now we report long term outcome of patients after a median follow up of 11 years with a focus on overall survival (OS) differences. Methods: Primary evaluation of TTF was performed according to a pre-planned modified intention to treat (ITT, mITT) strategy with correction for interim analyses (overrunning analysis); all other efficacy analyses are according to strict ITT. TTF and OS were described by Kaplan-Meier estimates and compared by two-sided log-rank tests. The trial was not powered to detect unadjusted OS differences; accordingly, in the present evaluation, the number of deaths yields a statistical power of 80% and 90% for overoptimistic OS hazard ratios of 0.67 and 0.63. Hazard ratios of R-DHAP vs. R-CHOP with two-sided 95% CI and the corresponding p values were calculated from a univariate Cox proportional hazards model and two multivariate Cox proportional hazards models, one adjusting for MIPI score, and the other adjusting for MIPI score and Ki-67 index, the two components of MIPI-c. We additionally evaluated cumulative incidence of secondary hematological malignancies, treating death without secondary hematological malignancy as competing event. Results: Of 497 patients randomized and evaluable according to ITT, 466 were included in primary evaluation. Median patient age was 55 years (range, 30-67), with MIPI and Ki-67 similar in two arms (MIPI Low 65%/60%, Intermediate 22%/26%, High 13%/14%; Ki-67≥30%: 28%/27%). In primary mITT analysis, TTF was still significant (p=0.038, HR: 0.59, both corrected for interim analyses). Differences in TTF were also confirmed in strict ITT analyses (Figure left; HRs unadjusted/adjusted for MIPI score/adjusted for MIPI-score and Ki-67: 0.60 (95% CI, 0.47-0.76)/0.56 (0.44-0.71)/0.52 (0.38-0.70), all p Conclusions: With additional 5 years of median follow-up, our results on first-line treatment of MCL patients younger than 66 years confirm the previously observed substantially prolonged TTF by the addition of high-dose ARA-C. When adjusting for MIPI without and with Ki-67 (conditional treatment effect), OS was significantly prolonged. In the future, avoidance of TBI and ASCT, as investigated in the TRIANGLE protocol, may reduce secondary malignancies after R-CHOP/R-DHAP. These data suggest that some patients may be functionally cured by optimal first line treatment and may challenge future chemotherapy-free strategies in MCL. Figure 1 Figure 1. Disclosures Walewski: Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Servier: Consultancy, Honoraria. Thieblemont: Gilead Sciences: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses , Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Bristol Myers Squibb/Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Cellectis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Hospira: Research Funding; Bayer: Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses . Salles: Epizyme: Consultancy, Honoraria; Velosbio: Consultancy; Loxo: Consultancy; Genmab: Consultancy; Incyte: Consultancy; Ipsen: Consultancy; Kite/Gilead: Consultancy; Janssen: Consultancy; Genentech/Roche: Consultancy; Miltneiy: Consultancy; Morphosys: Consultancy, Honoraria; Rapt: Consultancy; Novartis: Consultancy; Allogene: Consultancy; Debiopharm: Consultancy; Takeda: Consultancy; Regeneron: Consultancy, Honoraria; BMS/Celgene: Consultancy; Beigene: Consultancy; Abbvie: Consultancy, Honoraria; Bayer: Honoraria. Feugier: ROCHE: Membership on an entity's Board of Directors or advisory committees, Other: Meeting travel funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel funding. Hübel: Celgene: Consultancy; Gilead: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; EUSA: Consultancy, Speakers Bureau; Servier: Consultancy, Speakers Bureau. Klapper: Takeda: Consultancy, Research Funding; Regeneron: Consultancy, Research Funding; Amgen: Research Funding; Roche: Consultancy, Research Funding. Unterhalt: Roche: Research Funding. Dreyling: Novartis: Consultancy, Speakers Bureau; Roche: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Gilead Kite: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy, Research Funding, Speakers Bureau; Astra Zeneca: Consultancy, Speakers Bureau; Amgen: Speakers Bureau; AbbVie: Research Funding; BeiGene: Consultancy, Speakers Bureau; Genmab: Consultancy; MorphoSys: Consultancy.

In sickle cell disease (SCD), the β6 Glu→Val substitution leads to sickle hemoglobin (HbS) polymerization and red blood cell (RBC) sickling. Transplantation of autologous, genetically modified hematopoietic stem/progenitor cells (HSPCs) represents a promising therapeutic option for patients lacking a compatible donor. We previously designed a lentiviral vector (βAS3 LV) expressing a potent anti-sickling βAS3 globin and demonstrated its safety and efficacy in SCD patient cells (Weber et al., 2018). In vitro and in vivo preclinical studies demonstrated the safety and efficacy of a gene therapy (GT) protocol based on the efficient transduction of plerixafor-mobilized SCD HSPCs by βAS3 LV. Based on these results a Phase 1/2 clinical trial (NCT03964792) started in January 2020. Three homozygous SCD patients (P1, P2 and P3) were recruited. Before GT, patients suffered from severe SCD symptoms that were not controlled despite of a strict adherence to the treatment. Plerixafor-mobilized HSPCs were transduced achieving a VCN of 0.9±0.2 in liquid culture, 1.6±0.3 in BFU-E and 0.8±0.2 in CFU-GM. The patients were hypertransfused to reach HbS levels Here, for the 3 patients we report the follow-up of 18 (P1), 10 (P2) and 6 (P3) months. No drug-related severe adverse events were observed. Importantly, no sign of clonal hematopoiesis was detected by NGS sequencing performed on the graft before and after transduction. Despite of the similar VCN in the drug product, gene marking in peripheral blood mononuclear cells was variable and ranged between 0.2 and 0.6, as measured at the last follow-up (0.4 in P1, 0.6 in P2 and 0.2 in P3). These results pinpoint the difficulty to estimate the gene marking, self-renewal and engraftment potential of HSCs in the grafts. P1 and P2 clinically benefit from the GT treatment despite they presented non-severe vaso-occlusive crises (VOCs) not requiring hospitalization (two for P1 at month 6 and 14 and one in P2 at month 8 post-GT). Despite the rapid resolution of these episodes, P1 started hydroxyurea at month 10 and stopped it at month 16. P2 initiated a phlebotomy program to treat liver iron overload and decrease viscosity. Intravascular hemolysis improved in P1 and P2, as shown by a decrease in plasma hemoglobin and heme, and an increase in hemopexin (HPX). Interestingly, in P1 a mild worsening occurred at the time of VOC. In P1 and P2, total bilirubin, a marker of extravascular hemolysis, decreased post-GT. Deformability, measured using osmoscan, improved in P1 and to a lesser extent in P2; however, both still exhibited some degree of dehydration compared to normal RBCs (Fig. 1). Adhesion to thrombospondin decreased after GT with an increase during VOC in P1 or prior the VOC in P2 (Fig. 1). In both patients, markers of inflammation (e.g., C reactive protein) and reticulocyte counts decreased upon GT. An in vitro sickling assays was performed for P1 and showed significant improvement, reaching a frequency of sickling cells similar to SCD heterozygous carriers (from 88% before GT to 45% 6 months post-GT). The GT treatment was not effective in P3 due to the modest intake and rapid decline of gene modified cells. In P1 and P2, who were no longer on transfusions, HbAS3 levels correlated with the VCN (2.1 g/dl for P1 and 3.3 g/dl for P2) and the therapeutic Hb accounted for 21.5%, and 28.7% of the total hemoglobins, respectively. For P3, who remained transfusion-dependent, this frequency was Overall, these clinical data indicate a variable efficacy of the DREPAGLOBE GT treatment, which likely depends on the extent of gene marking achieved in HSCs in vivo and on the engraftment capability of genetically modified HSCs in SCD patients' bone marrow. Single-cell RNA-seq analysis of HSPCs and evaluation of the bone marrow niche in SCD patients will aid to define critical parameters for achieving successful outcomes in GT clinical trials for SCD. Figure 1 Figure 1. Disclosures Joseph: bluebird bio: Consultancy. El Nemer: Hemanext: Consultancy. Bartolucci: INNOVHEM: Other: Co-founder; AGIOS: Consultancy; GBT: Consultancy; Bluebird: Consultancy, Research Funding; Jazz Pharma: Other: Lecture fees; Fabre Foundation: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Lecture fees, Steering committee, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy; Hemanext: Consultancy; Addmedica: Consultancy, Other: Lecture fees, Research Funding; Emmaus: Consultancy. Cavazzana: Smart Immune: Other: co-founder.

Background: The development of next generation sequencing techniques has brought important insights into the molecular mechanisms of erythropoiesis and how these processes can be perturbed in human diseases. This strategy may be valuable in some hereditary erythroid disorders where a subset of patients does not carry any mutations in the supposed causal gene and for which transgenic mouse models do not recapitulate the phenotype, suggesting that additional genetic events may be involved in pathogenesis. Here, we report the case of an adult patient presenting with atypical pure red cell aplasia associated with facial dysmorphy and chronic leg ulcers. Whole exome sequencing revealed a heterozygous missense mutation (R725W) in the CDAN1 gene, which has been previously reported in congenital dyserythropoietic anemia type I (CDAI). However, this mutation was also detected in her healthy brother, suggesting that this event alone was not sufficient to explain her phenotype. According to this hypothesis, we found an additional germline heterozygous nonsense mutation (Q732X) in the MMS22L gene, which was not shared by her unaffected relatives. MMS22L is a protein involved in homologous recombination-dependent repair of stalled or collapsed replication forks. Additionally, MMS22L is able to bind newly synthesized soluble histones H3 and H4 and exhibits a histone chaperone activity. MMS22L loading onto ssDNA during homologous recombination is promoted by the histone chaperone ASF1. Interestingly, CDAN1 acts as a negative regulator of ASF1 by mediating its sequestration in the cytoplasm, which results in the blocking of histone delivery. Aims: As MMS22L has never been reported in erythropoiesis before, we aimed to investigate the role of MMS22L in human erythropoiesis. Based on the data summarized above, the purpose of this study was also to determine the effect of combined inactivation of MMS22L and CDAN1 on in vivo erythropoiesis, while exploring the functional cooperation between both proteins. Results: To decipher the role of MMS22L in human erythropoiesis, we assessed the consequences of complete MMS22L inactivation in human cord blood CD34+ progenitors as well as in CD36+ immature erythroblasts using shRNA lentiviruses. This resulted in a severe decrease of cell proliferation and differentiation due to G1 cell cycle arrest, with a slight increase of apoptosis. Interestingly, this phenotype was not observed when MMS22L was inactivated in the granulo-monocytic lineage, in which differentiation was maintained, suggesting that erythroid cells, that are highly proliferative, are more sensitive to MMS22L inactivation. To better understand the effect of combined CDAN1 and MMS22L haploinsufficiency observed in the proband, we used zebrafish as an in vivo model. Mms22l and cdan1 expression were simultaneously or separately downregulated by about 50% using antisens morpholino oligomers. 48 hours later, zebrafish embryos were stained with o-dianisidine to detect hemoglobin-containing cells. We found that combined knock-down of mms22l and cdan1 resulted in severe anemia, while knock-down of mms22l or cdan1 alone did not lead to any erythroid disorder. This experiment provides a proof-of-concept, indicating that the phenotype of the proband is indeed caused by the combination of both MMS22L and CDAN1 mutations. Finally, in order to decipher the cooperation between MMS22L and CDAN1 we used the human erythroid UT-7 cell line. We found that CDAN1 inactivation resulted in a severe decrease in MMS22L expression within the nucleus, suggesting that CDAN1 may regulate MMS22L expression or localization. We therefore wanted to confirm these results by assessing MMS22L expression in B-EBV cell lines established from two CDAI patients with CDAN1 compound heterozygous mutations. We found a great decrease in MMS22L expression within the nucleus of the CDAI patients' cells when compared to three control B-EBV cell lines. Based on these results, we suggest that impairment of MMS22L trafficking to the nucleus could be involved in CDA1 physiopathology. Conclusion: Through comprehensive genetic analysis of a single case with atypical congenital anemia, we demonstrated for the first time that MMS22L, a cell cycle regulator, is essential for the process of erythropoiesis. The crosstalk between MMS22L and CDAN1 is currently under investigation and could bring important new insights into the physiopathology of CDAI. Disclosures Hermine: Novartis: Research Funding; Alexion: Research Funding; AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Celgene BMS: Consultancy, Research Funding; Roche: Consultancy.

Introduction: Congenital neutropenia (CN) is characterized by chronic neutropenia due to a constitutional genetic defect.1 To date, these diseases have not been considered to be frequently associated with malignant solid tumors, unlike the risk of secondary myelodysplastic syndrome leukemia, which is well-known in CN. Methods: The French Severe Chronic Neutropenia Registry (FSCNR) has prospectively enrolled CN patients since 1993. Solid tumors, identified during routine patient follow-up, were classified according to WHO criteria. We included localized lymphoma in the spectrum of malignant solid tumors. We calculated the incidence of malignant solid tumors in a cohort of CN patients. Results: Among 868 patients with various CN subtypes followed for a total of 16617 person-years, 24 patients who developed a malignant solid tumor were identified. Those cancers are described in Table 1, including the CN genetic anomaly. Cancers were almost always diagnosed in adulthood, with median age at diagnosis of 38.1 (range 10-72) years; only 3 cancers were diagnosed before age of 20 years. The cancer rate was 1.2% at 30 years of age, 7% at 40 years and 24% at 50 years (Fig. 1A). The risk-of-cancer percentages depended mainly on the associated genetic deficiency. Solid tumors were roughly distributed as follows: 33% among WHIM (CXCR4) patients, 5.3% among GATA2 patients, 2.7% among ELANE patients, 1.9 % among SBDS patients and 0.8% among for all other subtypes combined (Fig. 1B). Human papillomavirus (HPV) was the cause of cancer for 2/5 in WHIM patients and 2/6 in GATA2 patients. Three Lymphoma were identified, one in GATA2 patient and 2 in WHIM patients. Notably, our cohort's follow-up is skewed to the right, with less efficient monitoring of adults, with still limited long-term follow-up beyond 40 years. Therefore, we probably underestimated the solid-tumor risk in CN patients, as many patients, if alive, are no longer followed in hematology centers. Among 103 patients who underwent hematopoietic stem-cell transplantation (HSCT), 76 were long-term survivors. None of them developed solid tumors, which differs strikingly from the high malignancy risk associated with Fanconi anemia post-HSCT. Lastly, the FSCNR also includes and follows patients with idiopathic neutropenia. Among the 232 idiopathic neutropenia patients, followed for a total of 2866 person-years, no malignancy has been observed so far. Conclusion: Our data lead us to advance that CN patients should be considered at risk of developing solid cancers, especially after the age of 30 years. This risk, at first glance, depended on the CN-associated genetic anomaly, with CXCR4 mutation, GATA2, SBDS and ELANE being the most frequent. HSCT was not associated with a higher risk and may, in contrast, be protective. These findings warrant confirmation but represent a compelling reason to prolong follow-up into adulthood of CN patients diagnosed during childhood. No indication was found of a specific high solid-tumor risk associated with idiopathic neutropenia. Reference Donadieu J, Beaupain B, Fenneteau O, Bellanne-Chantelot C. Congenital neutropenia in the era of genomics: classification, diagnosis, and natural history. Br.J.Haematol. 2017; 179(4): 557-574. Acknowledgments: The French SCN registry is supported by grants from Amgen, Chugai, Prolong Pharma, X4 Pharma, Inserm, the Association 111 les Arts, the Association RMHE, the Association Sportive de Saint Quentin Fallavier. The authors thank the association IRIS and Mrs Grosjean and Mr Gonnot(ASSQF), the association Barth France for their support. Disclosures Hermine: Roche: Consultancy; Celgene BMS: Consultancy, Research Funding; AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Alexion: Research Funding; Novartis: Research Funding. Blaise:Jazz Pharmaceuticals: Honoraria. Sicre de Fontbrune:Alexion Pharmaceuticals Inc.: Honoraria, Research Funding. cohen Beaussant:X4 Pharmaceuticals, Inc.: Current Employment.

Introduction: β-thalassemia is a genetic blood disorder characterized by ineffective erythropoiesis and anemia. Although RBC transfusions are a key supportive treatment for patients (pts) with anemia due to β-thalassemia, they may be associated with life-threatening complications including iron overload. Luspatercept, a first-in-class erythroid maturation agent, is approved by the FDA for the treatment of anemia in adult pts with β-thalassemia requiring regular RBC transfusions. Here we present a longitudinal analysis of the benefits of luspatercept on RBC transfusion burden (TB) in the BELIEVE trial, a phase 3, double-blind, randomized, placebo (PBO)-controlled study evaluating the efficacy and safety of luspatercept in adult pts with β-thalassemia requiring regular RBC transfusions (NCT02604433; Cappellini MD, et al. N Engl J Med 2020;382:1219-31). Methods: Pts were aged ≥ 18 y with β-thalassemia or hemoglobin (Hb) E/β-thalassemia (compound β-thalassemia mutation and/or multiplication of α-globin genes was allowed) and required regular RBC transfusions (6-20 RBC units in the 24 wks prior to randomization, no transfusion-free period > 35 days). Pts were randomized 2:1 to luspatercept 1.0 mg/kg (up to 1.25 mg/kg allowed) or PBO subcutaneously every 3 wks for ≥ 48 wks. Pts in both treatment arms continued to receive best supportive care, including RBC transfusions to maintain target pretransfusion Hb levels and iron chelation therapy. After study unblinding, pts randomized to PBO were eligible to cross over to receive luspatercept in an open-label phase. Mean RBC units transfused and mean change in RBC TB and number of visits were assessed in luspatercept (by primary endpoint responders and non-responders) and PBO arms during the first 48 wks. Long-term changes in RBC TB and visits in luspatercept pts remaining on treatment were assessed every 24 wks from treatment initiation to data cutoff (July 1, 2019). Results: Of 336 pts enrolled, 224 were randomized to the luspatercept arm and 112 to PBO. During the 24 wks prior to randomization, median RBC TB was 14.3 RBC units (range 6.0-26.0) and median pretransfusion Hb level was 9.27 g/dL (range 4.5-11.7). As of July 1, 2019, median treatment duration for pts in the luspatercept and PBO (prior to crossover) arms was 119.1 and 74.7 wks, respectively. 68.2% of pts initially randomized to the luspatercept arm were still receiving treatment at the end of 2 y. Pts in the luspatercept arm experienced a mean change of −2.20 RBC units/24 wks transfused vs +0.72 RBC units/24 wks in PBO-treated pts during Wks 1-24 compared to baseline (least squares [LS] mean difference −2.95; 95% confidence interval [CI] −3.59, −2.32; P < 0.001) (Table A). In Wks 25-48, mean changes of −2.53 and +0.21 RBC units/24 wks transfused were reported in luspatercept- and PBO-treated pts, respectively (LS mean difference −2.76; 95% CI −3.46, −2.06; P < 0.001). During Wks 1-24 and 25-48, luspatercept responders (defined as pts achieving ≥ 33% reduction in RBC TB during Wks 13-24, with a reduction of ≥ 2 RBC units, vs baseline) experienced mean transfusion reductions of −5.32 and −4.83 RBC units/24 wks, respectively, and luspatercept non-responders experienced mean changes of −1.30 and −1.85 RBC units/24 wks. Luspatercept-treated pts continued to experience durable, sustained reductions in RBC units up to 144 wks of follow-up (Table B). During Wks 1-24, luspatercept-treated pts experienced a mean change of −0.49 in transfusion event frequency vs +0.32 for PBO-treated pts (LS mean difference −0.78; 95% CI −1.16, −0.40; P < 0.001) (Table A). Mean changes in transfusion visits of −0.54 and +0.14 were experienced by pts in the luspatercept and PBO arms, respectively, during Wks 25-48 (LS mean difference −0.65; 95% CI −1.03, −0.26; P = 0.001). Luspatercept responders and non-responders reported mean reductions in transfusion visits during Wks 1-24 (−1.38, P < 0.001 and −0.23, P = 0.006, respectively) and Wks 25-48 (−1.09, P < 0.001 and −0.38, P = 0.010, respectively) vs baseline. Sustained reductions in transfusion visits persisted for over 2 y; as the BELIEVE trial is still ongoing, only a small number of pts could be evaluated at later time points (Table B). Conclusions: Luspatercept was associated with sustained reductions in RBC transfusion units and visits in responders and non-responders during the first 48 wks vs PBO. Pts on luspatercept continued to experience reductions in RBC TB and events over 2 y. Figure 1 Disclosures Taher: BMS: Consultancy, Research Funding; Ionis Pharmaceuticals: Consultancy; Vifor Pharma: Consultancy, Research Funding; Silence Therapeutics: Consultancy; Novartis Pharmaceuticals: Consultancy, Research Funding. Viprakasit:Agios Pharmaceuticals, Ionis Pharmaceuticals, La Jolla Pharmaceuticals, Protagonist Therapeutics, Vifor Pharma: Consultancy, Research Funding; BMS, Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau. Hermine:Roche: Consultancy; Celgene BMS: Consultancy, Research Funding; AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Alexion: Research Funding; Novartis: Research Funding. Porter:Protagonist Therapeutics: Honoraria; Vifor Pharmaceuticals: Honoraria; Silence Therapeutics: Honoraria; La Jolla Pharmaceuticals: Honoraria; Agios Pharmaceuticals: Consultancy, Honoraria; BMS: Consultancy, Honoraria; bluebird bio, Inc.: Consultancy, Honoraria. Piga:BMS: Research Funding; Novartis: Research Funding. Kuo:Pfizer: Consultancy, Research Funding; Bioverativ: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria; Alexion: Consultancy, Honoraria; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Apellis: Consultancy; Bluebird Bio: Consultancy. Coates:Celgene, BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sangamo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios pharma: Consultancy, Honoraria; apo pharma (Chiesi Pharma): Consultancy, Honoraria; Vifor Pharma: Consultancy, Honoraria. Voskaridou:ACCELERON Company: Consultancy, Research Funding; BMS: Consultancy, Research Funding; PROTAGONIST Company: Research Funding; ADDMEDICA Company: Consultancy, Research Funding; NOVARTIS Company: Research Funding; GENESIS Company: Consultancy, Research Funding. Kattamis:Agios: Consultancy; Ionis: Membership on an entity's Board of Directors or advisory committees; Vertex: Membership on an entity's Board of Directors or advisory committees; Vifor: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Apopharma/Chiesi: Honoraria, Speakers Bureau; Genesis Pharma SA: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Shetty:BMS: Current Employment, Current equity holder in publicly-traded company. Zhang:BMS: Current Employment. Tian:BMS: Current Employment. Miteva:BMS: Current Employment. Zinger:Celgene International, A Bristol-Myers Squibb Company: Current Employment. Tang:BMS: Current Employment, Current equity holder in publicly-traded company. Backstrom:Acceleron Pharma: Current Employment, Current equity holder in publicly-traded company; BMS: Current equity holder in publicly-traded company. Cappellini:BMS: Honoraria; CRISPR Therapeutics, Novartis, Vifor Pharma: Membership on an entity's Board of Directors or advisory committees; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Patients (pts) with transfusion-dependent (TD) β-thalassemia may require long-term red blood cell transfusions (RBCT) that can lead to iron overload and associated complications, which impact negatively on health-related quality of life (HRQoL). Administration of RBCT provides transient relief from anemia-related symptoms associated with β-thalassemia; reduction of RBCT may increase anemia-related symptoms and thereby worsen HRQoL. The phase 3 BELIEVE study (NCT02604433) showed that the first-in-class erythroid maturation agent luspatercept provided clinically meaningful reduction in RBCT burden, but the impact of luspatercept on HRQoL is not well understood. This analysis assessed the effect of luspatercept plus best supportive care (BSC, including RBCT, iron chelation therapy) vs placebo (PBO) plus BSC on HRQoL in pts with TD β-thalassemia. Methods: Pts received luspatercept (starting dose 1.0 mg/kg with titration up to 1.25 mg/kg every 3 weeks) or PBO, subcutaneously for ≥ 48 weeks plus BSC. HRQoL was assessed using the generic 36-item Short Form Health Survey (SF-36) and the thalassemia-specific Transfusion-dependent Quality of Life questionnaire (TranQol), at screening (≤ 4 weeks prior to first study dose) and every 12 weeks up to 48 weeks of treatment. The HRQoL evaluable population included all pts who completed the HRQoL assessment at screening and ≥ 1 post-screening assessment visit. The TranQol and SF-36 were considered complete if ≥ 75% and ≥ 50% of items, respectively, were answered at a given time point. The primary analysis assessed changes from baseline between groups up to Week 48. The primary domains of interest were: TranQol total score and Physical Health (PH); and the SF-36 Physical Component Summary (PCS), Physical Functioning (PF), and General Health (GH). Other domains were considered exploratory domains. Changes from baseline were compared using ANCOVA models adjusting for baseline domain scores and geographic region. In exploratory analyses, the proportion of pts achieving a clinically meaningful improvement in domain scores were compared between pts on luspatercept achieving a clinical response (≥ 50% reduction in RBCT burden over 12 weeks; ≥ 33% reduction in RBCT burden over 12 weeks; transfusion independence [TI] any 8 weeks; or TI any 12 weeks), and PBO. Results: 336 pts were randomized to treatment; 224 to luspatercept and 112 to PBO. The HRQoL evaluable population was 212 (94.6%) in the luspatercept arm and 104 (92.9%) in the PBO arm. HRQoL questionnaire compliance rates among pts still on treatment were > 87.5% for both questionnaires at Week 48. Baseline HRQoL scores were similar to the US general population for most SF-36 domains, although GH, Role-Emotional, and Role-Physical domain scores were impaired in the BELIEVE population. Mean scores on all primary and exploratory domains were stable over time in both treatment groups and did not differ between treatment groups at Week 24 and 48. When considering responders to luspatercept, pts receiving luspatercept and achieving a ≥ 50% reduction in RBCT burden over 12 weeks were significantly more likely than pts receiving PBO to have a clinically meaningful improvement in PCS (31.1% vs 16.5%; P = 0.024), and PF (30.0% vs 13.2%; P = 0.007) at Week 48 (Table). Statistically significant differences between luspatercept and PBO were also seen among pts achieving TI for any 8 or any 12 weeks for some SF-36 domains, but no statistical difference was seen in pts achieving a ≥ 33% reduction in RBCT burden for either SF-36 or TranQol domains although the proportion of pts with improved scores was higher with luspatercept, especially at Week 48. Conclusions: Overall, the addition of luspatercept to BSC reduced transfusion burden while sustaining TranQol and SF-36 HRQoL scores over time through Week 48 compared with those receiving PBO. Pts with TD β-thalassemia responding to luspatercept were more likely to achieve clinically meaningful improvements in HRQoL compared with PBO. Disclosures Cappellini: Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; CRISPR Therapeutics, Novartis, Vifor Pharma: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria. Taher:Silence Therapeutics: Consultancy; Vifor Pharma: Consultancy, Research Funding; Ionis Pharmaceuticals: Consultancy; BMS: Consultancy, Research Funding; Novartis Pharmaceuticals: Consultancy, Research Funding. Piga:BMS: Research Funding; Novartis: Research Funding. Shah:Novartis, BMS: Consultancy, Honoraria, Speakers Bureau; Bluebird Bio: Consultancy, Honoraria; IQVIA: Consultancy, Membership on an entity's Board of Directors or advisory committees. Voskaridou:ADDMEDICA Company: Consultancy, Research Funding; BMS: Consultancy, Research Funding; ACCELERON Company: Consultancy, Research Funding; PROTAGONIST Company: Research Funding; GENESIS Company: Consultancy, Research Funding; NOVARTIS Company: Research Funding. Viprakasit:Agios Pharmaceuticals, Ionis Pharmaceuticals, La Jolla Pharmaceuticals, Protagonist Therapeutics, Vifor Pharma: Consultancy, Research Funding; BMS, Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau. Porter:Silence Therapeutics: Honoraria; La Jolla Pharmaceuticals: Honoraria; Vifor Pharmaceuticals: Honoraria; Protagonist Therapeutics: Honoraria; BMS: Consultancy, Honoraria; Agios Pharmaceuticals: Consultancy, Honoraria; bluebird bio, Inc.: Consultancy, Honoraria. Hermine:AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; BMS, Alexion, Novartis, Inatherys: Research Funding. Neufeld:Takeda: Consultancy; Octapharma: Consultancy; Novo Nordsik: Consultancy; genetech: Consultancy; Bayer: Other: DSMB; Imara Pharma: Other: DSMB service; ApoPharma/Chiezi: Other: DSMB service; Pfizer: Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy; Acceleron Pharma: Consultancy, Other: DSMB. Thompson:BMS: Consultancy, Research Funding; Baxalta: Research Funding; Novartis: Consultancy, Honoraria, Research Funding; CRISPR/Vertex: Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Biomarin: Research Funding. Tang:BMS: Current Employment, Current equity holder in publicly-traded company. Yu:Evidera: Current Employment. Guo:BMS: Consultancy. Shetty:BMS: Current Employment, Current equity holder in publicly-traded company. Miteva:BMS: Current Employment. Zinger:Celgene, a Bristol Myers Squibb company: Current Employment. Backstrom:Acceleron Pharma: Current Employment, Current equity holder in publicly-traded company; BMS: Current equity holder in publicly-traded company. Oliva:Abbvie: Consultancy; Amgen: Consultancy; Novartis: Consultancy; BMS: Consultancy, Honoraria, Patents & Royalties, Speakers Bureau; Alexion: Consultancy; Apellis: Consultancy.

Background : AETHERA randomized controlled study (Moskowitz, Lancet 2015) showed that the administration of Brentuximab Vedotin (BV) maintenance after autologous stem cell transplantation (ASCT) improved progression free survival (PFS) in BV-naive refractory/relapsed (R/R) Hodgkin lymphoma (HL) patients. However, since BV approval for R/R HL in 2012, many patients are receiving salvage BV before ASCT, alone or combined with chemotherapy. In the AMAHRELIS retrospective nationwide French study, we investigated the real-life outcome of patients with R/R HL mostly treated with BV-based salvage therapies and who received post-ASCT BV maintenance. Objectives : As primary 0objective, we assessed 2 years-PFS of patients treated with post-ASCT BV maintenance from 2012 to 2017 in France. As secondary objectives, we correlated variables (such as use of salvage BV before ASCT, centrally reviewed TEP-assessed response) with survival, and evaluated reported tolerance of BV using the CTCAE v4.0 criteria. Methods : We conducted this observational retrospective study in 58 national centers. Inclusion criteria were R/R HL patients who received at least two infusions of BV after ASCT, at the exclusion of patients in progression after transplant. Among 1134 patients who underwent ASCT for R/R HL between 2012 and 2017 in France based on the French society of bone marrow transplantation database, 835 (74%) patients were screened and data were available for 794 (70%) patients. FDG-PET scan at relapse and before transplantation were recorded and centrally reviewed (still ongoing). FDG-PET scan were reported using the Deauville score (DS), and complete remission was defined by a DS < 4. Post-transplant status was evaluated based on CT-scan or on FDG-PET scan results. This study was approved by the SFGMTC and the LYSA. Results : Fifteen percent (115/794) of patients met eligibility criteria, and were enrolled in this study. Among them, 95% met inclusion criteria for BV maintenance according to the AETHERA study as primary refractory disease (43%), early relapse (27%) or extranodal disease (49%). The mean number of BV injections after ASCT was 11 (3-18). Patients characteristics were : mean age was 34 y (range between 16-70y), 54% were male, and 57% of patients were stage III or IV at relapse. Notably, 70% of patients received BV as salvage therapy and 81% achieved a complete remission before ASCT. The median follow-up period was 35 months. The 2 years survival for the whole cohort was 75,3% for PFS (95% CI : 68,4-84,3) and 96,4% for overall survival (95% CI : 94,2-100) (Figure 1). The use of BV as part of salvage therapy before transplant had no impact on PFS. We observed a trend to an increased occurrence of neuropathy in patients receiving BV before transplant without impact on early treatment discontinuation. We tested several variables for correlation with survival using a univariate Cox model including high risk patients defined as primary refractory disease or early relapse and disseminated disease, extranodal relapse, use of BV before transplant, number of salvage lines, remission status before and after transplant (complete response versus partial response or stable disease), time between ASCT and BV onset and number of BV cycles after transplant. Among these variables, high risk status, less than 10 post transplant BV cycles and absence of post transplant complete remission significantly correlated with a reduced survival probability, and remained significant after analysis using a multivariate Cox model (Table 1). Conclusion : From the real-life AMAHRELIS study, we confirmed the very good outcome of R/R HL patients in the era of post-transplant BV maintenance, with a 2y-PFS of 75% similar to the results of the AETHERA landmark study (2y-PFS of 63%). The results of current strategies with pre- and post-transplant BV outperformed historical series based on high dose therapies, including those of tandem transplant for high risk patients. Future studies incorporating BV strategies with immune checkpoint inhibitors might improve outcome in R/R HL patients. Disclosures Meignan: ROCHE: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Sibon:takeda france: Consultancy. Stamatoulas Bastard:Pfizer: Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Celgene: Honoraria; Takeda: Consultancy. Fornecker:Takeda: Consultancy; Roche: Consultancy. Casasnovas:Takeda: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Roche: Consultancy, Honoraria, Other: travel, accomodations, expenses, Research Funding; Gilead: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Abbvie: Consultancy, Honoraria; MSD: Consultancy, Honoraria; Amgen: Consultancy, Honoraria. Cartron:Gilead: Honoraria; Jansen: Honoraria; Abbvie: Honoraria; Celgene: Consultancy, Honoraria; Sanofi: Honoraria; F. Hoffmann-La Roche: Consultancy, Honoraria. Ghesquieres:Gilead: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; CELGENE: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Roche: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Janssen: Honoraria. Brice:Takeda: Consultancy; Roche: Consultancy. Hermine:AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Celgene BMS: Consultancy, Research Funding; Roche: Consultancy; Novartis: Research Funding; Alexion: Research Funding. Rubio:Medac: Consultancy; Gilead: Honoraria; MSD: Honoraria; Novartis: Honoraria; Neovii: Research Funding. Deau Fischer:Takeda: Consultancy; Roche: Consultancy.

INTRODUCTION : Minimal residual disease (MRD) has emerged as an important predictor of clinical outcome in patients with mantle cell lymphoma (MCL). Its use in everyday clinical practice, however, remains uncertain since standardized MRD monitoring strategies and response criteria are not yet formally established. To address this question, we conducted the LyMa-MRD project as an ancillary biology study in a prospective phase III trial in MCL patients < 66 years of age (NCI NCT00921414; LyMa Trial; Le Gouill et al, NEJM 2017). Briefly, in this trial all patients were previously untreated and received 4 courses of R-DHAP followed by ASCT. After ASCT, patients were randomized between observation (obs) versus Rituximab maintenance (RM) which was associated to superior event free, progression free and overall survival, respectively. Herein, we present the final MRD analysis. METHODS : The final MRD analysis was performed in a total of 220 MRD evaluable patients [defined as patients with an available MRD assay and appropriate follow-up sample in peripheral blood (PB) and/or bone marrow, (BM), at the time point of interest for statistical analyses] and aimed to assess MRD response rates and prognostic impact [progression free and overall survival, (PFS, and OS, respectively)] at the pre-ASCT (after induction phase) (n=195 ; 86 RM and 84 obs) or (2 ; 90 RM and 92 obs). Sequential MRD monitoring was a predefined secondary objective. An additional aim was to assess the value of combining molecular MRD and PET (positron emission tomography) for outcome prediction pre- and post-ASCT. MRD was quantitatively assessed in PB and / or BM after induction or after ASCT by using gold standard EURO-MRD RQ-PCR assays targeted to clonal immunoglobulin gene rearrangements, in 3 French national reference laboratories. MRD data for survival analysis was generated from assays with a minimal sensitivity of at least 10-4. MRD status was assigned according to EURO-MRD interpretation guidelines. MRD negativity at a given time point was defined as absence of RQ-PCR amplification product in the follow-up sample (minimal assay sensitivity of 10-4). Non evaluable MRD was mostly due to no follow-up sample, no MRD target or MRD assay failure. RESULTS: In a total of 195 MRD evaluable patients who completed R-DHAP induction therapy, MRD was found negative in 77% (n=144) and 64% (n=115) of PB and BM samples, respectively. MRD status pre-ASCT was predictive of PFS and OS: p< 0.0001, respectively, for PB; p= 0.0295 and 0.0407, respectively, for BM). Post-ASCT, MRD in PB and BM was negative in 94% (n=181) and 81% (n=137) of patients, respectively, and was predictive of PFS (but not OS) (PB, p= 0.0452 ; BM, p=0.0261). In patients that were MRD negative either pre (PB, p= 0.0260; BM, p=0.0405) or post-ASCT (PB, p=0.001; BM, p=0.007), RM was associated to improved PFS and also OS, albeit to a lesser extent [pre-ASCT BM MRD and post-ASCT PB MRD neg groups only ; p= 0.0395 and p =0.02, respectively]. Finally, combining PET and MRD status offered improved prediction of PFS both pre- (p< 0.0001, PB; p=0.0028, BM MRD) and post-ASCT (p CONCLUSION: Pre-ASCT MRD status in both BM and PB is an early predictor of PFS and OS in younger MCL patients receiving ASCT. RM provides longer PFS and OS regardless of MRD status pre- and post-ASCT. Early sequential MRD monitoring at the pre-ASCT treatment phase and directly post-ASCT thus offers strong potential for early clinical outcome prediction, as a surrogate clinical end point, and for MRD-guided, risk-adapted treatment in MCL. Disclosures Delfau-Larue: MUNDIPHARMA: Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AMGEN: Honoraria; GILEAD: Honoraria; ROCHE: Honoraria. Thieblemont:Roche, Hospita: Research Funding; Roche, Amgen, Kyte Gilead, Celgene, Abbvie, Novartis, Cellectis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Cellectis: Speakers Bureau. Oberic:Roche, Janssen: Consultancy; Roche, Janssen: Other: Travel, Accommodations, Expenses; Roche: Honoraria. Bouabdallah:Gilead Sciences: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Roche: Consultancy, Honoraria. Casasnovas:MSD: Consultancy, Honoraria; AMGEN: Consultancy, Honoraria; BMS: Consultancy, Honoraria; abbvie: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Ribrag:BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Expenses; argenX: Current equity holder in publicly-traded company, Research Funding; Infinity: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; arGEN-X-BVBA: Research Funding; BAY1000394 studies on MCL: Patents & Royalties; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees; Eisai: Honoraria; MSD: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Immune Design: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; Epizyme: Consultancy, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AZD: Honoraria, Other; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Institut Gustave Roussy: Current Employment; Nanostring: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Expenses; Pharmamar: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Hermine:Alexion: Research Funding; AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Novartis: Research Funding; Roche: Consultancy; Celgene BMS: Consultancy, Research Funding. Le Gouill:Roche Genentech, Janssen-Cilag and Abbvie, Celgene, Jazz pharmaceutical, Gilead-kite, Loxo, Daiichi-Sankyo and Servier: Honoraria; Loxo Oncology at Lilly: Consultancy.

Introduction: Regular red blood cell (RBC) transfusions are the main supportive treatment for chronic anemia due to β-thalassemia. Transfusion-dependent pts require ICT to prevent iron overload from RBC transfusions, and associated complications. Thus, there is a clinical need to reduce transfusions and iron burden in pts with anemia due to β-thalassemia. Luspatercept, an erythroid maturation agent, is approved by the FDA for treatment of anemia in adult pts with β-thalassemia who require regular RBC transfusions. The phase 3, double-blind, randomized, placebo (PBO)-controlled BELIEVE study is evaluating the efficacy and safety of luspatercept in adult pts with β-thalassemia requiring regular RBC transfusions (NCT02604433; Cappellini MD, et al. N Engl J Med 2020;382:1219-31). Here we assess the effect of long-term luspatercept use on iron loading and ICT use in the BELIEVE trial. Methods: Pts were ≥ 18 years with β-thalassemia or hemoglobin (Hb) E/β-thalassemia (compound β-thalassemia mutation and/or multiplication of α-globin genes was allowed) and required regular RBC transfusions (defined as 6-20 RBC units in the 24 wks prior to randomization with no transfusion-free period > 35 days). Pts were randomized 2:1 to luspatercept 1.0 mg/kg (up to 1.25 mg/kg allowed) or PBO subcutaneously every 3 wks for ≥ 48 wks. Pts in both treatment arms continued to receive RBC transfusions to maintain target pretransfusion Hb levels, as well as ICT (deferasirox, deferoxamine, and deferiprone alone or in combination) per product label and physician practice prior to randomization. After study unblinding, pts randomized to PBO were eligible to cross over to luspatercept in an open-label phase. Risk for iron overload-related complications was evaluated by stratifying pts into categories based on serum ferritin (SF) level (< 1,000 μg/L, 1,000 to < 2,500 μg/L, ≥ 2,500 μg/L), liver iron concentration (LIC; ≤ 3 mg/g dw, > 3 mg/g dw), and myocardial iron (by T2* MRI; ≤ 20 ms, > 20 ms). Long-term changes in SF and ICT use were assessed in luspatercept pts remaining on treatment up to data cutoff (July 1, 2019) or study discontinuation, whichever was earlier. Results: Of 336 pts enrolled, 224 were randomized to luspatercept and 112 to PBO. Mean baseline SF, LIC, and myocardial T2* for luspatercept vs PBO arms were 2,097 vs 1,845 μg/L, 12.0 vs 10.1 mg/g dw, and 33.5 vs 34.8 ms, respectively. Overall, 97.3% of pts received ICT at baseline. As of July 1, 2019, 67.9% of pts initially randomized to luspatercept were still receiving treatment at the end of 2 years; 92 (82.1%) PBO pts crossed over to luspatercept after study unblinding. Of 141 luspatercept-treated pts with baseline mean SF ≥ 1,000 μg/L, 24 (17.0%) pts achieved post-baseline mean SF < 1,000 μg/L when assessed over Wks 1−24, vs 3 (5.0%) PBO-treated pts. During Wks 73−96, 26/56 (46.4%) luspatercept pts with baseline mean SF ≥ 1,000 μg/L achieved post-baseline mean SF < 1,000 μg/L (Figure A). At Wks 24 and 48, 5/120 (4.2%) and 13/134 (9.7%) luspatercept pts, respectively, shifted from LIC > 3 mg/g dw at baseline to ≤ 3 mg/g dw, vs 4/61 (6.6%) and 4/68 (5.9%) PBO pts; 15/105 (14.3%) of luspatercept pts shifted from LIC > 3 mg/g dw at baseline to ≤ 3 mg/g dw at Wk 96. 6/30 (20.0%) pts receiving luspatercept shifted from myocardial iron T2* ≤ 20 ms at baseline to > 20 ms at Wk 48 (vs 1/11 [9.1%] PBO pts); at Wk 96, 6/24 (25.0%) luspatercept-treated pts shifted from ≤ 20 ms to > 20 ms. During Wks 1-12, mean daily deferasirox dose in luspatercept pts was 1,477.08 mg (mean change from baseline +136.27 mg) and 1,516.28 mg (mean change from baseline +131.80 mg) in PBO pts. No significant difference was seen between luspatercept and PBO arms during the first 48 weeks, however, the proportion of patients receiving ≥ 1 ICT gradually declined in both luspatercept responders (defined as pts achieving ≥ 33% reduction in transfusion burden from baseline during Wks 13−24) and non-responders over time (Figure B). Both luspatercept responders and non-responders also experienced a gradual decrease in mean daily dose of deferasirox over time (Figure C). Conclusions: Compared with PBO-treated pts, a higher proportion of luspatercept-treated pts shifted to lower SF, LIC, and myocardial iron levels during the first 48 wks, indicative of lower risk of iron overload complications. Long-term luspatercept treatment led to an increasing proportion of patients with SF < 1,000 μg/L and decreasing trends of overall ICT use and deferasirox dosage. Figure 1 Disclosures Hermine: Celgene BMS: Consultancy, Research Funding; AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Alexion: Research Funding; Roche: Consultancy; Novartis: Research Funding. Cappellini:CRISPR Therapeutics, Novartis, Vifor Pharma: Membership on an entity's Board of Directors or advisory committees; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria. Taher:Novartis Pharmaceuticals: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Ionis Pharmaceuticals: Consultancy; Vifor Pharma: Consultancy, Research Funding; Silence Therapeutics: Consultancy. Coates:Sangamo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios pharma: Consultancy, Honoraria; Celgene, BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; apo pharma (Chiesi Pharma): Consultancy, Honoraria; Vifor Pharma: Consultancy, Honoraria. Viprakasit:BMS, Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Agios Pharmaceuticals, Ionis Pharmaceuticals, La Jolla Pharmaceuticals, Protagonist Therapeutics, Vifor Pharma: Consultancy, Research Funding. Voskaridou:ADDMEDICA Company: Consultancy, Research Funding; NOVARTIS Company: Research Funding; GENESIS Company: Consultancy, Research Funding; PROTAGONIST Company: Research Funding; ACCELERON Company: Consultancy, Research Funding; BMS: Consultancy, Research Funding. Lal:Chiesi USA: Consultancy; Novartis: Research Funding; Celgene, BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding; La Jolla Pharmaceutical Company: Research Funding; bluebird bio, Inc.: Research Funding; Insight Magnetics: Research Funding; Terumo Corporation: Research Funding; Protagonist Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios Pharmaceuticals: Consultancy. Perrotta:Acceleron Pharma: Research Funding; Celgene, BMS: Honoraria; Novartis: Honoraria, Research Funding. Kattamis:Genesis Pharma SA: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Apopharma/Chiesi: Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Ionis: Membership on an entity's Board of Directors or advisory committees; Vertex: Membership on an entity's Board of Directors or advisory committees; Vifor: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy. Shetty:BMS: Current Employment, Current equity holder in publicly-traded company. Zhang:BMS: Current Employment. Tian:BMS: Current Employment. Miteva:BMS: Current Employment. Zinger:Celgene International, A Bristol-Myers Squibb Company: Current Employment. Tang:BMS: Current Employment, Current equity holder in publicly-traded company. Backstrom:BMS: Current equity holder in publicly-traded company; Acceleron Pharma: Current Employment, Current equity holder in publicly-traded company. Porter:Agios Pharmaceuticals: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Protagonist Therapeutics: Honoraria; Silence Therapeutics: Honoraria; La Jolla Pharmaceuticals: Honoraria; Vifor Pharmaceuticals: Honoraria; bluebird bio, Inc.: Consultancy, Honoraria.

Introduction Rituximab maintenance (RM) (375mg/m2 per infusion every 2 months for 3 years) in transplanted patients with mantle-cell lymphomas (MCL) prolongs disease control (LyMa trial, Le Gouill et al NEJM; NCT00921414). However, post-transplant RM might also induce long-term immune deficiency and thus increases risk of infection. To address these issues, we performed an ancillary pre-planned study based on the LyMa trial, a phase III trial that compared RM versus observation (Obs) after ASCT in MCL patients. We compared post-transplant immune-deficiency and its impact on PFS and OS in the RM vs Obs groups. Method All transplanted and randomized patients enrolled in the LyMa trial were eligible for the present study. The following data were collected during the post-ASCT period and monitored according to protocol procedure: febrile event, clinically documented infection, hospitalization for infection, neutropenia, hypogammaglobulinemia and T CD4 lymphocytes count. We also retrospectively collected the use of immune globulin (Ig) substitution. In the LyMa trial, patients were randomized between RM vs Obs after transplantation. To decipher the implication of ASCT or RM in immune recovery, treatment periods were divided in 4: < 6 months after randomization, from 6 to 12 months after randomization, from one to two year after randomization, and from 2 to 3 years after randomization (respectively periods A, B, C and D). Chi-square or Fisher's exact tests were used as appropriate to investigate differences between arms in each treatment period. For all tests, a two-sided p-value Results 240 patients were eligible, 120 in each arm. Patients' characteristics at diagnosis and inclusion were similar in the two arms. Number of hospitalizations due to infections was not statistically different in RM vs Obs in all periods. As previously shown, grade 3/4 infections incidence did not differ in the 2 arms. However, febrile events were more frequent in the RM arm (32 pts vs 11; 38 events vs 12) but this was statistically significant only in C and D periods; p=0,03 for the 2 periods. In all, 51 infections in 44 pts were reported in Obs vs 127 events in 82 pts in RM arm. This difference was also only statistically significant during the C period, p=0,001. Grade 4 neutropenia incidence and T CD4 count did not differ between the two arms in all tested periods. Hypogammaglobulinemia was statistically more frequent in RM during C and D periods (p=0,0001 and p< 0,0001, respectively). Mean level of gammaglobulinemia on D period was 6,50 g/L (range 0,6-11,7) in obs arm versus 4,99 (range 1,0-9,5) in RM arm (p< 0,0001). 36 pts in RM arm vs 10 pts in obs arm were substituted with Ig and the difference was statistically significant only in period D, p Febrile and infectious episodes; neutropenia and T CD 4 lymphopenia did not modify PFS and OS. Patients with gammaglobulinemia < 6g/L in RM arm and in the whole cohort had longer PFS compared to pts who did not present hypogammaglobulinemia : 3-years PFS 93,2% vs 63,5% in RM arm HR = 0,294, 95% CI (0,113-0,767 and), p=0,01 and 3-years PFS 85,6% vs 63,6% in the whole cohort, HR adjusted on treatment arm=0,488 95% CI (0,287-0,830), p=0,008 . PFS was not modified by gammaglobulin level in the Obs arm and it did not modified OS in both arms. We performed a multivariate analysis to determine which data were predictive of infectious events and delayed immune recovery (neutropenia, hypogamma, T CD 4 lymphopenia). This included all univariate parameters with p value < 0,2, among clinical and biological characteristics at diagnosis, response after induction and number of rituximab injections. Interestingly, among others expected parameters, complete response assessed by TDM was predictive of hypogamma with Odd Ratio 2,972 (1,263-6,994) p=0,0126. No value was predictive of neutropenia or T CD4 cytopenia. Conclusion As compared to observation, the use of post-transplant RM does not increase risk of neutropenia and T CD4 lymphopenia. However febrile and infectious events, hypogammaglobulinemia and Ig substitution are more frequent after one year post transplantation. Hypogamma < 6g/L is associated with longer PFS and complete morphologic response. This suggests that hypogammaglobulinemia could be a surrogate for disease response quality and duration. Our findings deserve to be confirmed. Disclosures Thieblemont: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Hospira: Research Funding; Cellectis: Speakers Bureau; Janssen: Honoraria; University Employement: Current Employment. Bouabdallah:Gilead Sciences: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Takeda: Consultancy, Honoraria. Oberic:Roche, Janssen: Other: Travel, Accommodations, Expenses; Roche: Honoraria; Roche, Janssen: Consultancy. Hermine:AB Science: Consultancy, Current equity holder in publicly-traded company, Honoraria, Patents & Royalties, Research Funding; Celgene BMS: Consultancy, Research Funding; Novartis: Research Funding; Alexion: Research Funding; Roche: Consultancy. Le Gouill:Loxo Oncology at Lilly: Consultancy; Roche Genentech, Janssen-Cilag and Abbvie, Celgene, Jazz pharmaceutical, Gilead-kite, Loxo, Daiichi-Sankyo and Servier: Honoraria.

TO THE EDITOR: Peripheral T-cell lymphomas (PTCLs) are heterogeneous diseases resulting from the malignant transformation of mature T or natural killer cells. Their epidemiology varies widely, but PTCLs that derive from T follicular helper (TFH) cells, which include angioimmunoblastic T-cell

On behalf of the Lymphoma Study Association (LYSA) Introduction: Aggressive Mantle Cell Lymphoma variant (A-MCL), including blastic and pleomorphic morphological variants, is a rare subtype of MCL whose frequency varies around 10-15% of all newly-diagnosed MCL patients. According to 2017 World Health Organization (WHO) classification, the diagnosis of A-MCL is based on morphology. A high proliferation rate on Ki-67 staining is not sufficient to be classified as a blastoid or pleomorphic subtype. This might induce diagnostic confusion. The aim of the present retrospective study is to investigate whether or not the CD71, c-Myc, SOX11, P53, ki67 and P16 expressions assessed by immunohistochemistry (IHC) can distinguish A-MCL from classical MCL (C-MCL). We also investigate the prognostic value of these markers in A-MCL patients. Methods: We re-investigated all MCL patients presented with A-MCL (n=110) at diagnosis and who have been enrolled in six prospective clinical trials. At time of inclusion, a centralized pathological review was performed to confirm the diagnosis of MCL. Cases were initially classified according to the 2008 WHO classification (LYMA, MCL-SA, MCL-SJ, RIBVD and RIPAD trials) or according to the 2017 WHO classification (MCLR2-ELDERLY trials). For the present study, we performed a supplemental pathology review by a panel of 5 hematopathologists experts from the LYSA group according to 2017 WHO classification. We identified 75 cases (out of 110) of A-MCL (8 blastic and 67 pleomorphic variants) which represent 15% of all MCL enrolled in these six trials. We have compared A-MCL characteristics to C-MCL who had specimens available for TMA (n=412 C-MCL out of 487 patients enrolled). IHC was performed on TMA, using the six selected antibodies and were scored by quantifying the percentage of cells stained on each spot. Patients available for survival analysis (53 A-MCL and 312 C-MCL) were drawn from all studies (except from the MCLR2-Elderly study that is ongoing). Different cut-offs were considered for progression free survival (PFS) and overall survival (OS) for each variable. The proliferation index was evaluated with Ki67 classical determination eyeballing and Ki67 reading by grid counting. Cut-offs for each of these markers were determined using X-tile software, which determines the optimal value for classifying patients into groups based on overall and progression-free survival. Results: At baseline, the aggressive forms were similar to classical forms in terms of demographic characteristics (age at diagnosis, localization and sex). p53 protein expression was significantly higher in A-MCL patients than in C-MCL (p10%), c-MYC (>30%) Ki67 (>40%) were associated with poorer OS and PFS in the cohort of A-MCL and C-MCL patients. There was no significant difference in survival both for OS and PFS regarding P53 (>30%). In multivariate analysis stratified by trial, Ki67 by grid>40% (HR=2.303[1.479-3.585] ; p =0.0002) and c-MYC >30% (HR=1.865 [1.060-3.279] p =0.0305) were predictive for OS whereas only Ki67 by grid >40% (HR=2.055 [1.434, 2.944], p Conclusion: CD71, c-Myc, P53 and P16 expression levels assessed by IHC are higher in A-MCL as compared to C-MCL. These markers could therefore be recommended in routine practice to distinguish between A-MCL and C-MCL. We also found that patients with Ki67 count by grid >40% had significantly shorter PFS and OS and patients with high Myc expression >30% had a significantly poorer OS. Thus, MYC expression and Ki67 by IHC is a suitable test for routine diagnostic practice to assess A-MCL prognosis. Disclosures Le Gouill: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Roche-Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support. Ribrag:argenX: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Epizyme: Honoraria, Research Funding; Infinity: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; AZ: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Membership on an entity's Board of Directors or advisory committees. Dreyling:Novartis: Other: scientific advisory board; Celgene: Consultancy, Other: scientific advisory board, Research Funding, Speakers Bureau; Acerta: Other: scientific advisory board; Janssen: Consultancy, Other: scientific advisory board, Research Funding, Speakers Bureau; Gilead: Consultancy, Other: scientific advisory board, Speakers Bureau; Sandoz: Other: scientific advisory board; Mundipharma: Consultancy, Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: scientific advisory board, Research Funding, Speakers Bureau; Bayer: Consultancy, Other: scientific advisory board, Speakers Bureau. Hermine:Celgene: Research Funding; Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding.

Introduction Adult T-cell leukemia/lymphoma (ATL) is a peripheral T-cell neoplasm triggered by HTLV1 infection. According to the Japanese studies, the median onset of disease is around age 60 (Yamada Y et al. Br J of Haematol 2001, Kamiunten A et al. Hematol Oncol 2018). The aggressive forms exhibit a poor prognosis, due to intrinsic or acquired chemotherapy resistance and severe immunosuppression. Combination chemotherapy can improve the response rates, and consolidation with allogenic hematopoietic stem cell transplantation (allo-HSCT) prolongs complete remission (CR) (Yamada Y et al. Br J of Haematol 2001, Kamiunten A et al. Hematol Oncol 2018). The overall survival (OS) rates at 1 and 2 years after transplantation were reported to be 34% and respectively 27% (Kamiunten A et al. Hematol Oncol 2018). Romania is one of the regions with the highest prevalence of HTLV1 infection (5.33 at 10.000 donors in 2003-2008, Leperche S et al. Vox Sang 2009), therefore the prevalence of ATL is also higher. Methods A prospective observational study was performed on all patients with aggressive forms of ATL, diagnosed in Bucharest between April 2010 and January 2019, respectively 56 patients. Patients under 18 years of age and with chronic or smoldering type were excluded. The goal of this study was to better describe the disease characteristics and to discover novel factors that influence response and survival. All patients were assessed in collaboration with Necker Hospital, Paris, France, as reference center. Clinical and lab data were collected, the treatment was administered at investigator choice using CHOP/CHOP-like, Hyper-CVAD and LSG15 regimens, and allo-HSCT was offered to all eligible patients as soon as CR was obtained. Statistical analyses were performed using IBM SPSS Statistics 25. For survival analysis we used Kaplan-Meier estimate. The ROC curve was used to set cutoff values. The statistical significance was calculated using Chi-squared test and Fisher's exact test. Results In this study we analyzed a total of 56 ATL patients (M:F=1:1.3), with a median age of 42.5 years, all having aggressive types. Within this group, 33.9% had hypercalcemia and 73.2% elevated LDH (64.3% >2xN). Most used chemotherapy regimens were: CHOP/CHOP-like (60.7%), followed by LSG15 (23.2%) and Hyper-CVAD (7.1%); antiretroviral therapy (51.8%) and allo-HSCT (12.5%) were also used. LSG15 regimen is not fully applicable in our country due to unavailability of Ranimustine and Vindesine, therefore a small proportion of patients received this treatment. In multivariate analysis, factors showing significant association with lower rate of CR were: age >40.5 years, leukocytosis with a cut-off of 8950/μl, hypercalcemia >9.5 mg/dl, high LDH >512 U/L. LSG15 was associated with a higher CR rate (50%) compared to CHOP/CHOP-like (22.7%) and Hyper-CVAD (33.3%), although not statistically significant. Median OS was 6.5 months (5.1 - acute type, 8.0 - lymphomatous type), versus 3.5 months in acute type and 9.5 months in lymphomatous type in previous data in our center. Early death rate (< 1 month) was found in 8.9% (n=5) of patients. Factors associated with early death were: acute type (n=4), leukocytosis (n=5), hypercalcemia (n=4), high LDH (n=5), extranodal involvement (n=4). Patients who obtained CR (n=9) had a better survival that those who did not (median OS 40.7 vs 5.1 months, p=0.000) (Fig a); undergoing allo-HSCT also significantly increased OS (median OS not reached vs 6.1 months, p=0.003) (Fig b). Among patients who underwent allo-HSCT, OS at 1 year and 2 years after the allo-HSCT were 57.1% and 42.9%, respectively. Three patients died, all less than 1 year after transplantation. Conclusions Median age at diagnosis in our group was lower (42.5 years) versus the Japanese studies (Yamada Y et al. Br J of Haematol 2001, Kamiunten A et al. Hematol Oncol 2018). This might reflect an origin of infection in the 1980s in Romania, where other outbreaks occurred by horizontal transmission in that period, including an outbreak of HIV-1 (Patrascu I V et al, Lancet 1990). Future in-depth studies of this cohort might better correlate age of infection, HTLV1 subtype and latency to ATL. The best predictors of better survival were obtaining CR and receiving allo-HSCT. Among the treatments we used, LSG15 regimen had higher rate of CR. Survival after transplantation was higher in our group compared to the Japanese studies (Kamiunten A et al. Hematol Oncol 2018). Disclosures Constantinescu: AgenDix GmbH: Other: Co-Founder, MyeloPro Research and Diagnostics; AlsaTech: Other: Co-Founde; Wiley & Sons: Other: Editor in Chief, Journal of Cellular and Molecular Medicine; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hermine:Celgene: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Novartis: Research Funding.

*° contributed equally to this work. Introduction: Systemic Mastocytosis (SM) is a heterogeneous disorder characterized by mast cells (MCs) accumulation in various tissues and associated with KIT mutations (KIT D816V) in more than 90% of the cases. It includes indolent (ISM) and advanced diseases (advSM), which are associated with additional molecular abnormalities. For advSM, recent clinical studies have shown that Midostaurin, a kinase inhibitor of WT and mutant KIT, induces high rate of responses associated with significant improvement of prognosis. However, complete responses are infrequent and relapses occur in a significant proportion of patients. Therefore, combination therapies are needed to increase overall response rate and prevent relapses. Venetoclax is a selective orally bioavailable BCL-2 inhibitor that induces cell death and is currently used for treatment of various lymphoid and myeloid malignancies. In an attempt to identify novel diagnostic and prognostic markers and potentially new therapeutic targets for mastocytosis, bone marrow sections of patients with different categories of mastocytosis were analyzed by IHC using anti-BCL-2 antibodies. BH-3 profiling was used to assess BH-3 proteins dependency, and sensitivity to Venetoclax alone or in combination of Midostaurin. Methods: Thirty-three adult patients were included in this preliminary study. According to the WHO classification, patients were classified as having ISM (n=10), Smoldering SM (SSM n=1), advSM (n=16, including SM-AHN (n=9), MC leukemia (MCL n=4), MC sarcoma (MCS n=2)). Most patients were KIT D816V (n=30; 90.9%); two MCL and one MCS exhibited extracellular and juxtamembrane mutations, respectively. Among these patients, 9 were treated with Midostaurin as first line therapy. Formalin fixed bone marrow sections were performed at diagnosis and during follow up. Mast cells were identified by Giemsa staining and as CD117 and tryptase positive cells. BCL-2 staining was performed by immunohistochemistry in formalin paraffin embedded fixed section. BCL-2 staining was considered as positive (>5%), heterogeneous (partial staining) or homogeneous (>80% positive cells), of high or low intensity (> or = or < to residual T cells). BH3 profiling was performed in ROSA KIT WT and ROSA KIT D816V using Cytochrome C upon exposure to distinct BH3 peptides/mimetics. Results: In ISM, BCL-2 staining was negative (n= 2/10) or when positive only in rare MCs (n=8/10), with low intensity. In contrast, all advSM cases were positive (16/16) with high (13/16), and homogeneous (6/16) staining. In MCL and MCS, BCL-2 staining was always positive with a homogeneous and high staining. In patients treated with Midostaurin, BCL-2 staining was performed before and three months after treatment initiation. Although MCs infiltration was reduced at least by 50% in all cases, number of BCL-2 positive cells and intensity of staining remain unchanged. In vitro, flow cytometry analysis showed that both MCL-like cell lines (ROSA KIT WT and ROSA KIT D816V) expressed BCL-2, MCL-1 and BCL-XL proteins. When treated with Midostaurin (200nM) for 48 hours, expression of BCL-XL and MCL-1 significantly decreased in MC lines especially the one with KIT D816V mutation. Interestingly, BCL-2 expression remained unchanged upon Midostaurin treatment, which was consistent with in vivo observations. Dynamic profiling performed in ROSA cell lines revealed that priming by midostaurin dramatically enhanced apoptotic dependencies to BCL-2 and other BH-3 proteins (>20% of apoptosis), especially in ROSA KIT D816V (figure). Conclusion: High expression of BCL-2 is associated with advSM and may participate to the pathogenesis of the disease, to its resistance to conventional chemotherapies and to partial resistance to Midostaurin. Consistent with its effect in reducing MCL-1 and BCL-XL expression, Midostaurin restored apoptotic dependency to BCL2 in human MCL-like cells, thereby suggesting that midostaurin could sensitize mast cell tumor to venetoclax. Our results provide thus a rationale to use a combination of Midostaurin and Venetoclax to treat AdvSM patients. Figure Disclosures Dubreuil: AB Science: Employment, Membership on an entity's Board of Directors or advisory committees, Research Funding. Hermine:AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. OffLabel Disclosure: Venetoclax preclinical studioes on mastocytosis

Introduction Most blood antigen-carrying proteins have important functions not only in red blood cells (RBCs) but also in other tissues. Hence, because of their polymorphisms and the existence of natural null phenotypes, blood groups also represent powerful tools to investigate human diseases. The PEL-negative rare blood type is one of the last with an unknown genetic basis. Family studies showed that the PEL-negative phenotype was inherited as an autosomal recessive trait, but the PEL locus remained undetermined since the first description of the corresponding antibody in French-Canadian individuals in 1996. Results Combining whole-exome sequencing and comparative global proteomic approaches using genomic DNA and red cell membrane proteins from four unrelated French-Canadian PEL-negative individuals and from controls, we identified i) the Multidrug Resistance-Associated Protein 4 (MRP4), also known as ABCC4, as the only missing protein in all PEL-negative RBCs and ii) a large deletion removing the last 10 exons of the ABCC4 gene. Western blot analyses confirmed that ABCC4 was present in the membrane of PEL-positive control RBCs but totally absent in the PEL-negative RBCs (Fig 1A). Western blot and flow cytometry analyses of transfected HEK293 cells revealed that over-expression of ABCC4 results in a significant increase in PEL antigen cell-surface expression (Fig 1B). Conversely, similar analyses of ABCC4-knockout K562 cells generated by the CRISPR-Cas9 strategy showed that the complete loss of ABCC4 abolished the expression of the PEL antigen (Fig 1C). PEL-negative individuals are therefore the first ever reported population lacking the complete expression of the ABCC4 protein. Surprisingly, despite the expected biological importance of ABCC4 as a cyclic nucleotide transporter, no apparent mutual symptoms or diseases were identified after investigation of the clinical history of the 12 PEL-negative members within the 4 families analyzed in this study. However, platelet investigation from one PEL-negative individual supported the role of this protein in the modulation of platelet aggregation, as previously observed in ABCC4-knockout mice studies To better understand the function of ABCC4 in mature RBCs, we measured the intracellular cGMP level in RBCs from 5 PEL-negative individuals and 5 controls. We showed that the cGMP level was not significantly impaired in the absence of ABCC4 suggesting that another cGMP transporter could compensate for the absence of ABCC4 on the RBC membrane. Interestingly, proteomic and flow cytometry analyses indicated that among the five other ABC transporters (ABCC1, ABCA7, ABCB6, ABCC5 and ABCG2) expressed on RBCs, only ABCG2 was increased in PEL-negative/ABCC4null RBCs compared to controls (1.3-fold; p=0.0007). This suggested that the absence of ABCC4 in PEL-negative individuals could be compensated by the over-expression of ABCG2. Our data, together with previous studies indicating that both ABCC4 and ABCG2 export cGMP, strongly suggest that the over-expression of ABCG2 in PEL-negative RBCs represents a compensatory mechanism for the lack of ABCC4, which could explain the absence of hematological abnormalities in PEL-negative individuals. Discussion Using genetic, molecular and cellular approaches, we demonstrated that ABCC4 is the gene underlying the novel PEL blood group system and that homozygosity for a large deletion in this gene is responsible for the rare PEL-negative phenotype. ABCC4 represents the third ABC transporter carrying a blood group system after ABCG2 (JR) and ABCB6 (LAN). The expression level of ABCC4 is strongly involved in drug resistance and toxicity, and in the clinical course of leukemia. As ABCC4 carries the PEL antigen, PEL phenotyping could be useful in the adjustment of an optimal drug dose and prevention of chemotherapy side effects in leukemia. Our findings are of immediate and important relevance in transfusion medicine and in a personalized medicine approach for chemotherapy treatment follow-up in leukemia. Furthermore, the exceptional natural "knockouts" of ABC transporters are highly valuable in understanding their function, not only in erythroid cells, but also in other cells or tissues. Disclosures Hermine: Novartis: Research Funding; Celgene: Research Funding; AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding.

AB8939 is a novel, synthesized, small-molecule microtubule-destabilizer drug with proven prolific and potent in vitro activity against numerous cancer cell lines. In vitro and ex vivo studies (reported separately) have determined that AB8939 is well-suited for the treatment of hematopoietic tumors, in particular relapsed/refractory or poor-prognosis acute myeloid leukemia (AML), notably being able to circumvent two major resistance mechanisms associated with AML (i.e. P-glycoprotein and myeloperoxidase-mediated resistance). The therapeutic potential of AB8939 was investigated further through a series of in vivo experiments using three patient derived xenograft (PDX) mouse models and a cytarabine (Ara-C) resistant mouse model (MOLM14). MOLM14 cells and selected PDX primary cells were transduced to constitutively express luciferase for bioluminescence monitoring of tumor growth. In an Ara-C-sensitive AML PDX mouse model (ex vivo IC50 response to Ara-C in survival/proliferation assays was 0.82 µM), AB8939 (6 mg/kg in weekly cycles of 5 consecutive days) showed a statistically significant, 10-fold decrease in the amount of blasts detected in blood following 14 days of treatment compared with control, and a superior treatment effect compared with Ara-C (single cycle of 10 mg/kg twice per day for 4 consecutive days) in terms of decreased blasts in blood. In an Ara-C-refractory AML PDX mouse model (ex vivo IC50 response to Ara-C in survival/proliferation assays was 6.4 µM), animals treated with single agent AB8939 (6 mg/kg in weekly cycles of 5 consecutive days) showed reduced disease progression compared with control and Ara-C (single cycle of 10 mg/kg twice per day for 4 consecutive days) as evidenced from at least 10-times fewer blasts in blood, spleen and bone marrow following 28 days of treatment. This effect was even more pronounced for the combination treatment of AB8939 and Ara-C, suggesting a synergistic response. In a PDX mouse model that is highly resistant to Ara-C (ex vivo IC50 response to Ara-C in survival/proliferation assays was 8.3 µM), AB8939 as a single agent or in combination with Ara-C showed a significant (P For the well-established xenografted MOLM14 mouse model, immune-deficient NSG (NOD scid gamma) mice (5 animals per group) were injected intravenously with MOLM14-luciferase cells and treated over a period of 21 days with single agent AB8939 (subcutaneous injection) at a dosage of 6 mg/kg every day or 12 mg/kg every other day; Ara-C (intraperitoneal injection, single cycle of 10 mg/kg twice per day for 4 consecutive days); or vehicle. AB8939 caused a significant dose-dependent reduction in tumor volume (p=0.001) and increased survival with respect to control or single agent Ara-C (median survival at 6 and 12 mg/kg was 39 and 42 days, respectively, corresponding to a 60% improvement compared with the control and Ara-C groups). A similar dosing schedule study showed single agent AB8939 at 6 mg/kg administered over 6 consecutive days (6 ON/1 OFF) was optimal with this cohort having a median survival of 59 days, corresponding to a 100% improvement over control. Overall, these in vivo data provide compelling proof-of-concept for AB8939 as a treatment of AML. AB8939 administered alone or in combination with Ara-C was demonstrated to significantly increase survival and reduce tumor growth as compared with single agent Ara-C in relevant animal models of AML. A first in human, phase 1 trial evaluating AB8939 in AML patients unfit to receive intensive chemotherapy in second and third-line has been initiated. Disclosures Goubard: AB Science: Employment. Humbert:AB Science: Employment. Mansfield:AB Science: Employment, Patents & Royalties. Hermine:AB Science: Membership on an entity's Board of Directors or advisory committees. Dubreuil:AB Science: Employment, Membership on an entity's Board of Directors or advisory committees, Research Funding. AB8939 Study Group:AB Science: Consultancy, Employment.

Background: Hemophagocytic lymphohistiocytosis (HLH) syndrome is due to an abnormal and sustained activation of T lymphocytes and macrophages releasing pro-inflammatory cytokines in the microenvironment. HLH is characterized by clinical and biological features that includes fever, hepatomegaly, splenomegaly, high ferritin level, pancytopenia and liver biology abnormalities. HLH is commonly divided into genetic/hereditary cases (HLHg) and non genetic/ sporadic (HLHs) with no hints for an inherited causes. However, similarity of both clinical symptoms and biological abnormalities between HLHg and HLHs raised, however, the hypothesis that HLHs could have a genetic component that may be related to HLHg. However contribution of genetic factors in both, pathophysiology and prognosis of sporadic hemophagocytic lymphohistiocytosis (HLHs) remains unknown. To explore the hypothesis of a genetic susceptibility in HLHs, from 2010 to 2017, we constituted a cohort of 205 HLHs patients (adults and children) and analysed genes involved in genetic HLH (HLHg). Methods: Patients fulfillied modified HLH-2004 diagnostic criteria. Data collected included (i) clinical and biological features, (ii) associated diseases (AID), (iii) infectious events, (iv) treatment, and (v) clinical outcome during one year of follow up. HLHg related genes LYST, PRF1, UNC13-D, STX11, STXBP2, RAB27A, SH2D1A, XIAP were NGS sequenced in 172 patients. Selected variants were (i) unknown but met at least two criteria among MAF10, and/or Polyphen HDIV (>0.485) (n=50), (ii) previously related to HLHg (n=2), PRF1 A755G/N252S (MAF 10 and Polyphen HDIV). Two control cohorts were selected, the first one using the variant files from the European subpopulation of the 1000 Genomes (1000G cohort, n=502) phase 3 project and the second one from the local in-house variants data base (in-house cohort, n=5092). Results: Patients presented with neoplasia (n=62), AID (n=46) in which infection was mainly Herpes virus (EBV) (> 80%), or no etiology (idiopathic) (n=64) with a greater infectious diversity. Fifty-two variants met the selection criteria, they were distributed overall in 115 alleles in 84/172 patients. Variants were globally heterozygous. They were recurrent with occurrence in 2 patients for STX11, RAB27A and LYST genes to 10 patients for the N252S and 18 patients for the p.Ala91Val in PRF1. Overall the frequency of individuals exhibiting at least one variant was significantly in excess (48.8%, n=84) in the HLHs versus in in-house (35.9%, n=1826) (p=0.001, CAST test) or versus in 1000G population patients (38.6%, n=194) (p=0.02, CAST test). Importantly, the distribution of patients carrying either 0, 1, 2, 3 or 4 mutated alleles in HLHs cohort was statistically different from the two control populations (Trend test: HLH vs in-house p Importantly, severe patients carried a significantly higher number of variants (1, 2 or 3) than the one with a better outcome (p Conclusion: The results presented in this study strongly support the hypothesis that HLHs has a genetic component when tested with genes of HLH. Overall, this results established clearly a genotype/phenotype correlation between presence of one or more filtered HLH genes variants and severity of the HLH syndrome in patients. Finally, we proposed a di/tri genic model as an expression of genetic component in sporadic HLH. Disclosures Hermine: Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding.

Background LentiGlobin gene therapy contains autologous CD34+ hematopoietic stem cells (HSCs) transduced with the BB305 lentiviral vector (LVV), encoding human β-globin with a T87Q substitution. This substitution confers anti-sickling properties to the gene therapy-derived hemoglobin (HbAT87Q) and allows for its quantification in transduced HSCs. The proof of concept for LentiGlobin gene therapy in patients with transfusion-dependent β-thalassemia (TDT) and sickle cell disease (SCD) was established in the recently completed HGB-205 study (NCT02151526). Herein, we provide the safety and efficacy outcomes and long-term follow-up data for all 7 treated patients, 4 with TDT and 3 with SCD. Methods Patients 5−35 years old with TDT (≥ 100 mL/kg of packed red blood cells [pRBCs]/year) or severe SCD (e.g., ≥ 2 acute chest syndromes [ACS] or ≥ 2 vaso-occlusive crises in the preceding year or the year before regular transfusions) were enrolled. CD34+ HSCs were obtained by mobilization and apheresis in patients with TDT or by bone marrow harvest in patients with SCD. Following collection, cells were transduced with the BB305 LVV. Patients underwent busulfan myeloablative conditioning and were infused with transduced cells. Patients were monitored for engraftment, adverse events (AEs), HbAT87Q levels, and other hematologic and clinical parameters. After 2 years in HGB-205, patients transitioned into the long-term follow-up study, LTF-303 (NCT02633943). Summary statistics are shown as median (min-max). Results As of June 2019, patients with TDT (n=4) and SCD (n=3) had a median follow-up of 49.6 (40.5-60.6) and 28.5 (25.5-52.5) months, respectively. Table 1 shows patient and drug product characteristics and several key efficacy outcomes. All patients achieved HSC engraftment. LentiGlobin safety profile was consistent with busulfan myeloablative conditioning and, in case of SCD, with the underlying disease state. The most common non-hematologic Grade ≥ 3 AEs post-LentiGlobin gene therapy (≥ 2 patients) for patients with TDT were stomatitis (n=4) and increased aspartate aminotransferase (n=2), and for patients with SCD were ACS (n=2) and vaso-occlusive pain (n=2). In all 4 patients with TDT, total Hb and HbAT87Q levels remained generally stable up to 5 years post-LentiGlobin infusion. Three of 4 patients achieved transfusion independence (TI; defined as weighted average Hb ≥ 9g/dL without pRBC transfusions for ≥ 12 months), for an ongoing duration of 56.3 (38.2-57.6) months. Weighted average total Hb during TI was 11.4 (10.5-13.0) g/dL. One patient has been off transfusions for 37.5 months and had total Hb of 7.7 g/dL, which was below the ≥ 9 g/dL requirement to meet the protocol definition of TI. At last visit, HbAT87Q levels in these 4 patients ranged from 6.2-11.2 g/dL, which contributed 73.8-86.8% of the total Hb. The first patient treated with LentiGlobin for SCD experienced one vaso-occlusive pain episode, which developed at 30 months after LentiGlobin gene therapy following a case of acute gastroenteritis with fever and dehydration. The second SCD patient had 2 serious AEs (SAEs) of ACS approximately 6 and 8 months after LentiGlobin gene therapy. The patient resumed chronic pRBC transfusions and hydroxyurea treatment and subsequently experienced 2 SAEs of vaso-occlusive pain; no additional SAEs of vaso-occlusive pain or ACS were reported during the last 16 months of follow-up after LentiGlobin infusion. The third SCD patient had no episodes of vaso-occlusive pain or ACS during 25.5 months of follow-up post-LentiGlobin gene therapy as of the data cut-off. Two patients with SCD who have been off chronic pRBC transfusions, showed improvement in hemolysis markers post-LentiGlobin treatment and stabilization of HbAT87Q expression at approximately 6 months post-LentiGlobin infusion. Total Hb levels for patients with SCD at last visit were 13.0 g/dL (patient 1), 9.4 g/dL (patient 2), and 9.8 g/dL (patient 3), with corresponding HbAT87Q contributions of 47.9%, 7.9%, and 25.8%, respectively. Summary With up to 5 years of follow-up, treatment with LentiGlobin gene therapy was well tolerated and resulted in improvement in hematologic parameters and disease-related symptoms. Further results from the completed study will be presented. Disclosures Hermine: Celgene: Research Funding; Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding. Brousse:bluebird bio, Inc: Consultancy; AddMedica: Consultancy. El Nemer:Hemanext: Other: Other. Bartolucci:Novartis: Membership on an entity's Board of Directors or advisory committees; AddMedica: Honoraria, Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; HEMANEXT: Membership on an entity's Board of Directors or advisory committees. Asmal:bluebird bio, Inc: Employment, Equity Ownership. Whitney:bluebird bio, Inc: Employment, Equity Ownership. Gayron:bluebird bio, Inc: Employment, Equity Ownership. Huang:bluebird bio, Inc.: Employment, Equity Ownership. de Montalembert:AddMedica: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio, Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Ribeil:bluebird bio, Inc: Employment, Equity Ownership. Cavazzana:SmartImmune: Other: Founder.

Introduction: Hairy-cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder with a favorable outcome thanks to treatment with purine analogues (PNA) like cladribine and pentostatin. Here, we updated the French national retrospective cohort of HCL after 10 years of follow-up, in order to evaluate the risk of second cancers in these patients. Methods: Data were collected up to June 2018 through a questionnaire sent to the members of the Société Française d'Hématologie, and centralized in the cohort database. We described the second malignancies observed during the follow-up, distinguishing second 'solid' cancers from second hematological malignancies. Then, using a Fine and Gray model, we performed a multivariate analysis in order to identify second cancer risk factors. Finally, to evaluate the excess of cancers in our cohort in comparison with the French general population, we calculated the standardized incidence ratio (SIR). Results: 279 patients (pts) from 19 centers were included in our retrospective cohort. The median age was 59 years old (range 29-88). 21% had an infectious disease at diagnosis, 23% had a familial history of cancer and 11% a personal history of cancer before HCL diagnosis. The median number of lines of treatments was 1 (0-7). PNA (cladribine or pentostatin) were the first therapeutic choice in frontline (75% of pts) and at relapse (69%). With a median follow-up of 127 months (2-413), the median overall survival for the overall study population was 328 months (95% CI 299-357) and the median relapse-free survival (RFS) was 136 months (95% CI 109-163). Pts treated with cladribine or pentostatin in first line had a statistically significant better RFS than pts treated with 'other' treatments (log rank test, p < 0.001). The 10-year cumulative incidence of relapse was 39% (95% CI 33-46). Pts who received treatments other than PNA in first line had a higher risk of relapse (Gray's test, p < 0.001). For pts receiving PNA in first and second lines, there was no difference in outcomes between those who switched PNA and those who did not. In this cohort, we observed 68 second malignancies during the follow-up: 49 solid cancers (most prevalent: prostate and non-melanoma skin cancers) and 19 hematological malignancies (most prevalent: monoclonal gammopathy of undetermined significance (MGUS) and myelodysplastic syndromes (MDS)). The median onset of second cancer, second solid cancer and second hematological malignancy from HCL diagnosis was 81 months, 99 months and 78 months, respectively. The median age at diagnosis of cancer, solid cancer and hematological malignancy was 70, 69 and 77 years old, respectively. Considering death as a competing risk, the 10-year cumulative incidence of cancer, solid cancer and hematological malignancy was 15% (95% CI 11-19), 11% (95% CI 7.2-15), and 5.0% (95% CI 2.8-8.2), respectively. In multivariate analyses, IFN treatment was associated with a decreased risk for all cancers (Fine and Gray regression model, subdistribution Hazard Ratio (sdHR) 0.53 (95% CI 0.29-0.97); p = 0.038), a familial history of cancer was a risk factor for solid cancers (sdHR 2.12 (95% CI 1.15-3.91); p = 0.017), a personal history of cancer was a risk factor for hematological malignancies (sdHR 3.47 (95% CI 1.14-10.55); p = 0.028). Even after excluding non-melanoma skin cancers and MGUS, there was an excess of cancers (SIR = 2.22), solid cancers (SIR = 1.81) and hematological malignancies (SIR = 6.67). Conclusions: In this updated real-world retrospective cohort with a long follow-up and most pts treated with PNA, we highlighted the importance and the excess of second cancers in HCL patients, in particular hematological malignancies. Figure Disclosures Paillassa: Janssen: Other: Bibliography board with young hematologists. Thieblemont:Roche: Honoraria, Research Funding; Gilead: Honoraria; Novartis: Honoraria; Kyte: Honoraria; Janssen: Honoraria; Celgene: Honoraria; Cellectis: Membership on an entity's Board of Directors or advisory committees. Hermine:AB Science: Membership on an entity's Board of Directors or advisory committees. Feugier:janssen: Honoraria, Research Funding, Speakers Bureau; gilead: Honoraria, Research Funding, Speakers Bureau; roche: Honoraria, Research Funding, Speakers Bureau; abbvie: Honoraria, Research Funding, Speakers Bureau. Troussard:Innate Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Other: Research Support; Sysmex: Other: Research Support.

Introduction: Adult T lymphoma (ATL) is a rare and aggressive disease shown to be consistently caused by the human T lymphoma virus I (HTLV-I). It generally occurs in Japan and Africa, with a low incidence in Europe. Romania is an exception to this rule, presenting an endemic representation of ATL. Aim: The aim of this study was to present our experience with allogeneic stem cell transplantation (alloSCT) for ATL. Methods: The current study was a retrospective analysis of the ATL cases that received alloSCT in the Fundeni Clinical Institute. The patients were included between January 2016 to April 2019. Results: A total of 7 patients were included in the present study, out of which 2 (28%) presented the acute form, while the rest presented the lymphomatous form. Four (57%) patients presented extranodal involvement, with 3 of those (75%), showing skin involvement. Of note, all patients presenting skin involvement also had bone marrow involvement. Thus, skin involvement was associated with a more advanced disease. Graft versus host disease (GvHD) was present in 4 (57%) patients, two of which were acute GvHD and two, chronic GvHD. Interestingly, the two patients that relapsed presented either acute or chronic GvHD, showing that the graft versus lymphoma (GVL) effect that can be observed in other lymphoma types is not observed in this cohort. Another noticeable observation is the fact that 4 out of the 6 patients tested for HTLV-I at 6 months post alloSCT presented a positive HTLV-I viral load. This event occurred, although, at 30 days, all patients presented 100% donor chimerism and the donor samples were negative for HTLV-I. This shows a possible imperfect jump of the HTLV-I from the recipient to the donor T lymphocytes or the possibility of a reinfection. Three (43%) patients presented a response less than complete remission (CR) after the first line of therapy, two of which progressed to death. The two deaths occurred at 14 and 15 months from the diagnosis, with the other follow-up periods in the cohort being higher than 26 months with the exception of one patient that had a follow-up of 6.8 moths from diagnosis. These two aforementioned patients were also the only ones to relapse thus far. Conclusion: For ATL, alloSCT represents a viable and potentially curative approach when used in chemosensitive disease. This being said, there are clear differences from other lymphomas, ATL having to be considered separately. Disclosures Tanase: Pfizer: Membership on an entity's Board of Directors or advisory committees; Bristol Myers: Consultancy. Hermine:Novartis: Research Funding; Celgene: Research Funding; AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding.

Introduction: BELIEVE is an ongoing phase 3, randomized, double-blind, placebo-controlled study evaluating the efficacy and safety of luspatercept, a first-in-class erythroid maturation agent, in adults with β-thalassemia requiring regular RBC transfusions (ClinicalTrials.gov identifier: NCT02604433). Treatment with luspatercept significantly reduced RBC transfusion burden and was associated with a favorable safety profile in this patient (pt) population (Piga A, et al. Blood. 2019;133:1279-89). Here we report iron-related efficacy endpoints of the BELIEVE study, including change from baseline in serum ferritin, liver iron concentration (LIC), and myocardial iron, as determined by T2*-weighted magnetic resonance imaging (MRI), and the effect of baseline iron levels on response to luspatercept. Methods: Adults with β-thalassemia or hemoglobin (Hb) E/β-thalassemia who required regular transfusions of 6-20 RBC units in the 24 weeks (wks) prior to randomization (with no transfusion-free period ≥ 35 days during that period) were randomized 2:1 to luspatercept (starting dose level 1.0 mg/kg; titration up to 1.25 mg/kg) or placebo, administered subcutaneously every 3 wks for ≥ 48 wks. Pts in both arms could receive RBC transfusions and iron chelation therapy (ICT) throughout the study to maintain their baseline Hb levels. Results: 332/336 randomized pts received treatment with luspatercept or placebo; 209/223 (93.7%) and 104/109 (95.4%) pts in the luspatercept and placebo arms had history of iron overload, defined as serum ferritin > 1,000 µg/L or LIC > 7 mg/g dry weight. 97.3% of luspatercept-treated and 97.2% of placebo-treated pts received ICT at baseline; 62.3%, 41.3%, and 37.2% received deferasirox, deferiprone, and deferoxamine, respectively, in the luspatercept arm, vs 57.8%, 36.7%, and 35.8% in the placebo arm. Fewer pts received ICT as combination therapy vs monotherapy (luspatercept arm: 28.6% vs 68.8%; placebo arm: 24.1% vs 72.3%, respectively). Mean baseline serum ferritin, LIC, and myocardial iron (by T2* MRI) for luspatercept vs placebo arms were 2,096.91 vs 1,845.05 μg/L, 12.04 vs 10.09 mg/g, and 33.52 vs 34.76 ms, respectively. As of Jan 7, 2019, 157 (70.4%) continue to receive luspatercept and 92 (84.4%) crossed over from the placebo arm. During the last 12 wks of the 48-wk randomized treatment period, mean change from baseline in serum ferritin was −248.02 μg/L vs +106.62 μg/L for pts in the luspatercept and placebo arms, respectively (least squares mean [LSM] difference: −347.80; P < 0.0001). 158/224 (70.5%) and 33/112 (29.5%) pts in the luspatercept and placebo treatment arms achieved a ≥ 33% reduction in RBC transfusion burden of ≥ 2 RBC units during any 12-wk interval. Among the responders, mean change from baseline in serum ferritin was −343.22 μg/L and +47.30 μg/L for pts receiving luspatercept and placebo, respectively (LSM difference: −389.50; P = 0.0047). Of 140 luspatercept-treated pts with baseline ferritin ≥ 1,000 μg/L, 29 (20.7%) achieved post baseline ferritin of < 1,000 μg/L when assessed over the entire treatment period; results were similar in responders and non-responders. During the treatment phase, mean change in myocardial MRI iron signal (T2*) from baseline to Wk 48 was −1.83 ms for luspatercept and +0.02 ms for placebo (LSM difference: −2.39; P = 0.0391). Over 96 wks, 6 (20%) luspatercept-treated pts with baseline myocardial iron ≤ 20 ms had post-baseline results > 20 ms; results were similar between responders and non-responders. Mean LIC changes from baseline to Wk 48 (mg/g dry weight) were +0.10 and +0.08 for luspatercept and placebo arms, respectively (LSM difference: +0.11; P = 0.8685). Over 96 wks, mean change in LIC among luspatercept-treated patients overall was −0.5 mg/g and −1.1 mg/g among responders. When assessing impact of baseline iron loading there was a general consistency in achievement of ≥ 33% reduction in RBC transfusion with luspatercept over any 12 wks, regardless of iron loading subgroup (baseline serum ferritin, LIC, and myocardial iron) (Table). Conclusions: Luspatercept treatment resulted in clinically meaningful reductions in serum ferritin levels. Baseline iron overload did not seem to affect response to luspatercept; treatment resulted in clinically meaningful reductions in RBC transfusion burden regardless of baseline serum ferritin level, LIC, or myocardial iron loading. Disclosures Porter: Celgene Corporation: Consultancy, Honoraria; Protagonist: Honoraria; Vifor: Honoraria; La Jolla: Honoraria; Agios: Consultancy, Honoraria; Silence Therapeutics: Honoraria; Bluebird Bio: Consultancy, Honoraria. Cappellini:Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Honoraria; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Vifor Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; CRISPR Therapeutics: Membership on an entity's Board of Directors or advisory committees. Coates:apo pharma: Consultancy, Honoraria, Speakers Bureau; agios pharma: Consultancy, Honoraria; celgene: Consultancy, Honoraria, Other: steering committee of clinical study; vifor: Consultancy, Honoraria. Hermine:AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Novartis: Research Funding; Celgene: Research Funding. Viprakasit:Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene Corporation: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding; Vifor: Consultancy, Research Funding; Ionis: Consultancy, Research Funding; La Jolla: Consultancy, Research Funding. Voskaridou:Genesis: Consultancy, Research Funding; Protagonist: Research Funding; Celgene Corporation: Consultancy, Research Funding; Acceleron: Consultancy, Research Funding; Addmedica: Membership on an entity's Board of Directors or advisory committees. Perrotta:Acceleron Pharma: Research Funding; Novartis: Honoraria, Research Funding. Kattamis:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Apopharma: Honoraria; Vertex: Membership on an entity's Board of Directors or advisory committees; ViFOR: Membership on an entity's Board of Directors or advisory committees; Ionis: Membership on an entity's Board of Directors or advisory committees; Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Shetty:Celgene Corporation: Employment, Equity Ownership. Kuo:Celgene Corporation: Employment, Equity Ownership. Miteva:Celgene International: Employment. Zinger:Celgene Corporation: Employment. Linde:Acceleron Pharma: Employment, Equity Ownership; Fibrogen, Inc.: Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Taher:Protagonist Therapeutics: Consultancy, Research Funding; La Jolla Pharmaceuticals: Consultancy, Research Funding; Celgene Corporation: Research Funding; Abfero: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; Ionis Pharmaceuticals: Consultancy. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

While acute myeloid leukemia (AML) is still associated with a low cure rate, recent advances in understanding its molecular complexity have significantly improved therapy for subgroups of patients, including those harboring FLT3, IDH1 or IDH2 mutations1. However, more than half of AML cases still lack a druggable oncogenic target. Human cancers frequently harbor mutations in RAS oncogene family members, including NRAS, KRAS and HRAS, which drive oncogenesis by augmenting cellular proliferation and survival. These are small protein GTPases, regulated by a switch between active GTP-linked and inactive GDP-bound states governed by a complex network of guanine exchange factors (GEFs, favoring RAS-GTP) and GTPase activating factors (GAPs, favoring RAS-GDP). RAS activation - due to either extrinsic recruitment by transmembrane tyrosine kinase receptors or intrinsic mutations - propagates through the downstream RAF/MEK/ERK and PI3K/AKT signaling pathways. Besides RAS-activating mutations conferring independence from physiological regulators, human cancers harbor mutations in other RAS network genes such as NF1 (encoding neurofibromin, a RAS GAP), BRAF or PTPN11 (encoding the SHP2 tyrosine phosphatase involved in RAS activation). Somatic alterations of RAS pathway genes, notably NRAS, KRAS, PTPN11 (missense mutations) and NF1 (mutations and deletions), are reported in up to 20% of AML cases2. Generally arising as late driver events, RAS pathway mutations participate in leukemogenesis through mitogen activated protein kinase (MAPK) activation. The anti-tumor activity of MEK inhibitors in Nras-mutated AML in mice and in some NRAS or KRAS-mutated AML patients suggests that deregulated RAS pathway signaling may represent a bona fide therapeutic target. However, strategies to inhibit RAS - indirectly in most cases - have been hampered by signaling feedback, redundancy and tumor heterogeneity 3. We identified 127 cases of AML with unmet therapeutic need within a cohort from which we excluded those with European leukemia network (ELN) favorable prognosis or FLT3-ITD mutations. Targeted next-generation sequencing revealed RAS pathway alterations in 50 patients (39.3%) and NF1 mutations and deletions, mostly large cytogenetically detected deletions, in 17 (14.8%). NRAS, KRAS, PTPN11, CBL and BRAF variants were detected in 13 (10.4%), 10 (7.9%), 9 (7.2%), 5 (3.9%) and 2 (1.6%) cases, respectively. Mutations in RAF1, RASA1, SOS1 and MAP2K2 were observed in a single case each. RAS pathway alterations appeared in the putative main leukemic clone as well as in subclones inferred from variant allele frequencies. Concurrent RAS pathway mutations were observed in nine cases. Among 79 patients homogeneously treated with intensive induction chemotherapy, RAS pathway alterations correlated with higher clinical proliferation markers (elevated white blood cell count, blast cell percentage and LDH levels) and reduced survival probability, particularly within the ELN intermediate-risk subgroup. We established robust models of RAS/MAPK activation through genetic NF1 disruption or expression of NRASG12D or PTPN11D61Y in growth factor (GF)-dependent cell lines. We assessed oncogenic addiction to the RAS pathway in these cells through GF-independence, increased RAS activity, faster propagation in immunocompromised mice and an exquisite sensitivity to pharmacological MEK inhibition in vitro and in vivo. High-content pharmacological screens with FDA-approved molecules identified pyrvinium pamoate, an anti-helminthic agent, as preferentially active in RAS-activated cells. This compound significantly impaired cell viability and colony formation in primary AML samples with RAS pathway alterations. Moreover, the combination of trametinib and pyrvinium pamoate demonstrated synergy in cell line models and even primary samples. While pyrvinium pamoate strongly inhibited mitochondrial respiration and induced metabolic reprograming towards increased glycolysis, trametinib impaired glycolysis and mitochondrial respiratory capacity, suggesting a mechanistic basis for the synergy observed. These data highlight the translational opportunity in developing pyrvinium pamoate for RAS pathway mutated AML. References 1. Raj RV et al. Leuk. Res. 2018;74:113-120. 2. Simanshu DK et al. Cell. 2017;170(1):17-33. 3.Ryan MB et al. Nat Rev Clin Oncol. 2018;15(11):709-720. Figure Disclosures Hermine: AB Science: Membership on an entity's Board of Directors or advisory committees. Tamburini:Novartis pharmaceutical: Research Funding; Incyte: Research Funding.

Background. Hematopoiesis is a highly regulated system where multiple, yet undiscovered, factors orchestrate the self-renewal of bone marrow stem cells and their differentiation into blood cells. Following acute stresses like infections, inflammation, chemotherapy or radiation, the hematopoietic system quickly adapts by a process termed "emergency" or "stress" hematopoiesis. For instance, switches from steady state to emergency granulopoiesis or emergency erythropoiesis have been described in response to infection or bleeding. We recently identified, both in human and murine erythroid progenitors, a functional cell-autonomous serotonergic network with pro-survival and proliferative functions. Furthermore, pharmacologic restoration of serotonin levels using selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, a common antidepressant, was demonstrated to rescue the anemic phenotype in mice models. Here, we hypothesized that serotonin also has a role on other hematopoietic lineages, and that the serotonergic system could be a valuable therapeutic target in radiation or chemotherapy-induced cytopenia. Moreover, as our previous work suggested a cross-talk between serotonin and erythropoietin, we postulate that serotonin could act in cooperation with known hematopoietic growth factors. Material and method. For mice models, we submitted C57BL/6 wild-type 8-10 weeks old mice to sub-lethal irradiation and monitored hematopoietic recovery through complete blood counts. We compared mice treated with fluoxetine administrated orally (~ 20 mg/kg/day in drinking water) to a control group, with or without hematopoietic growth factors. For the retrospective human cohort, we used a computerized database to identify patients who underwent autologous hematopoietic stem cell transplantation (ASCT) in the adult hematology department of Necker hospital between 2008 and 2018. We compared 22 patients treated with an SSRI to 66 controls, matched according to number of injected CD34+ cells/kg, age, sex, conditioning chemotherapy, pathology, depth of response before transplantation, previous lines of chemotherapy, and year of transplantation. The study was conducted according to the Declaration of Helsinki. Results. First, we confirmed that, following sub-lethal irradiation, pharmacologic restoration of 5-HT levels in mice using fluoxetine improved normalization of the erythroid lineage (at day 17 post-irradiation, mean hemoglobin was 8.1 versus 2.8 g/dL in the fluoxetine versus control group (p=0.0002)). Second, the data revealed that the use of SSRI lead to a more rapid restoration of the leukocytes and platelets levels (at day 17 post-irradiation, mean leukocyte level was 1740 versus 314/mm3 (p Third, we observed an additive effect between fluoxetine and Granulocyte-Colony Stimulating Factor (G-CSF) on the recovery of the three myeloid lineages (at day 17 post-irradiation, mean hemoglobin was 10.5 versus 4.0 g/dL (p Finally, analysis of the in vivo murine model under steady state condition showed that without any hematopoietic stress, fluoxetine did not impact hematopoiesis. In human, analysis of the retrospective ASCT cohort demonstrated that patients treated with SSRI had a more rapid neutrophil recovery than matched control patients (mean duration of neutropenia Conclusion. In this work, we report a previously unknown role of SSRI in the hematopoietic recovery of cytopenia, both after sub-lethal irradiation in mice and after autologous hematopoietic stem cell transplantation in human. We also observed a significant cooperation between SSRI and G-CSF on the three myeloid lineages. We propose that the serotonergic system could be a valuable therapeutic target in stress hematopoiesis such as in therapy-induced aplasia in patients. Disclosures Hermine: AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. OffLabel Disclosure: Fluoxetine is a selective serotonin reuptake inhibitor for oral administration. It is an antidepressant approved for major depressive disorder, obsessive compulsive disorder, bulimia nervosa and panic disorder. We believe its role on serotonin can improve hematopoiesis.

INTRODUCTION: Mantle cell lymphoma (MCL) is a distinct lymphoma subtype with a wide variation of clinical course. Previously a clinically defined risk score (MIPI) was established which partly reflects the heterogeneity of clinical outcome in this disease (Hoster, JCO 2004). Based on prospective trials, cytology (classical type vs. blastoid variant; Hoster, JCO 2016), cell proliferation as determined by Ki-67expression (Hoster, JCO 2016), and p53 alterations (Eskelund, Blood 2017; Aukema, Blood 2018) all have been identified as major drivers of a rapidly progressing disease, independent of MIPI. Aim of this study was to assess the clinical outcome of patients with at least one of these 3 different biological risk factors in a large uniformly treated patient population. METHODS: All patients were treated in the MCL Younger (Hermine, Lancet 2016) and MCL Elderly trials (Kluin-Nelemans, NEJM 2012) of the European MCL Network. Formalin fixed paraffin embedded (FFPE) diagnostic patients' material was classified as classical or blastic/pleomorphic variant and analyzed by Ki-67 or p53 immunohistochemistry on either tissue microarrays or whole tissue sections. Patients were classified as having high risk biology if they displayed blastoid cytomorphology, Ki-67 ≥30% according to the published guidelines, or high p53 staining indicating a mutated gene status expression. As control, standard risk disease patients had classical MCL with low Ki-67 RESULTS: In 365 MCL (MCL younger: n=192, MCL elderly: n=173) out of 1229 study patients, at least one of the biological parameters indicated a high risk biology, or high risk biology was excluded by determination of all 3 parameters. No major survival difference was observed for patients with and without IHC data available, excluding a major selection bias. 65 of 319 analysed cases displayed a blastoid cytomorphology (20%), 175 of 345 cases had an increased Ki-67>30% (51%), and 54 of 254 cases displayed a mutated p53 status (21%). Based on the selection procedure of the cases, a total of 224 cased displayed a high risk biology (63%) vs 130 cases with confirmed standard risk disease(37%). Median failure-free (6.3 years vs, 2.2 years; p< 0.0001) and overall survival (median not reached vs. 4 years; p CONCLUSIONS: Although our enrichment strategy does not allow the estimation of the frequency of high risk biology and the patient group with standard risk disease is underrepresented in this evaluation, the patients with high risk biology as defined by blastoid variant, Ki-67 >30%, or high p53 expression had a significantly shorter failure-free and overall survival even without consideration of the clinical features of the disease (MIPI). As these biological factors seems to dictate the sometimes dismal clinical course of the disease, we recommend to incorporate these factors in routine diagnostic practice. Future studies should investigate the differential impact of targeted therapies in this biologically defined subset of patients. Disclosures Dreyling: Sandoz: Other: Scientific advisory board; Roche: Other: Scientific advisory board, Research Funding, Speakers Bureau; Novartis: Other: Scientific advisory board; Mundipharma: Other: Scientific advisory board, Research Funding; Janssen: Other: Scientific advisory board, Research Funding, Speakers Bureau; Gilead: Other: Scientific advisory board, Speakers Bureau; Celgene: Other: Scientific advisory board, Research Funding, Speakers Bureau; Acerta: Other: Scientific advisory board; Bayer: Other: Scientific advisory board, Speakers Bureau. Hoster:Roche Pharma AG: Other: Travel support; Janssen: Research Funding. Unterhalt:F. Hoffmann-La Roche: Research Funding. Hermine:AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. Klapper:Roche, Takeda, Amgen, Regeneron: Honoraria, Research Funding.

Background Hypothermic storage of red blood cell (RBC) concentrates for up to 42 days is associated with biochemical, molecular, morphological, and mechanical modifications. This "storage lesion" increases with storage duration and is associated with increased clearance of transfused storage-damaged RBCs from the recipient's circulation in the first few hours post-transfusion. This rapid clearance reduces transfusion efficacy, but how it occurs is not fully elucidated. RBCs with reduced surface area called "storage-induced micro-erythrocytes" (SMEs) were recently described. Their proportion increases from 2% to 23% during storage. Their reduced surface-to-volume ratio is expected to induce rapid mechanical clearance by the spleen. We aimed to evaluate whether SMEs can be used as a marker of transfusion efficacy, if this subpopulation of RBCs is preferentially cleared by the spleen after transfusion, and if so, by which mechanisms. Methods We evaluated the proportion of SMEs in stored RBC concentrates in vitro using ImageStream and correlated it to the 51Chromium-labeled 24h post-transfusion recovery (24hPTR) in vivo in 31 healthy human volunteers. We then investigated the fate of SMEs during 8 ex vivo perfusions of human spleens (16 RBC concentrates stored for 35-42 days). Finally, we developed a mouse transfusion model to assess the fate of SMEs in vivo and determine their main mechanisms of clearance. Results The proportion of SMEs in RBC concentrates at day 42 of storage correlated negatively with 24hPTR in healthy volunteers (r=-0.42, P5 passages through the spleen). The percentage of SMEs correlated with splenic retention rate ex vivo (r=0.46, p In our mouse transfusion model, SMEs accumulated during RBC storage. The 24hPTR also decreased with storage duration (64% on Day 14 vs. 95% on Day 1). The decrease in 24hPTR of long-stored RBCs was mostly due to clearance of the SME subpopulation. SME and morphologically normal long-stored RBC subpopulations displayed clearances of 83% and 13%, respectively. Stored RBCs accumulated predominantly in the spleen post-transfusion, and were mainly ingested by macrophages. In macrophage-depleted mice, 24hPTR improved (from 64% to 79%), splenic accumulation and clearance of SMEs were delayed, and the proportion of inflammatory monocytes increased and mediated clearance. In splenectomized mice, clearance of SMEs was not delayed, but increased accumulation was observed in the liver and bone marrow, and increased erythrophagocytosis by inflammatory monocytes was also observed. Conclusions We show that the proportion of SMEs correlates with 24hPTR in healthy human volunteers and with retention in human spleens perfused ex vivo. In vivo mouse data confirms these findings, showing that SMEs are cleared from the recipient circulation during the 24h following transfusion. Clearance of SMEs is delayed in macrophage-depleted mice, suggesting a central role of macrophages in this process. The human spleen is also likely to clear SMEs from the recipient's circulation, as suggested by experiments with human spleens perfused ex vivo. However, the spleen is not required, because SME clearance is not affected in splenectomized mice. This suggests that other organs may compensate to remove SMEs and highlights the importance of eliminating these morphologically-altered RBCs. Finally, quantification of SMEs is an operator-independent, reproducible marker of transfusion efficacy. It can be used to assess the potential of new processes to prepare and store RBC concentrates. Pre-transfusion quantification of SMEs could benefit chronically transfused patients, for whom improved transfusion efficacy is expected to reduce transfusion-induced iron overload. Disclosures Roussel: Zimmer Biomet: Research Funding. MARIN:Zimmer Biomet: Research Funding. Spitalnik:Hemanext: Membership on an entity's Board of Directors or advisory committees; Tioma, Inc.: Consultancy. Hermine:AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. Buffet:Zimmer Biomet: Research Funding. Amireault:Zimmer Biomet: Research Funding.

Introduction: β-thalassemia is an inherited hemoglobinopathy characterized by ineffective erythropoiesis and anemia. Luspatercept is a first-in-class erythroid maturation agent that binds to select TGF-β superfamily ligands to reduce aberrant Smad2/3 signaling and enhance late-stage erythropoiesis. We aim to evaluate in detail the number of response episodes, duration of clinical benefit, and safety in luspatercept responders during the phase 3 BELIEVE study (NCT02604433). Methods: Eligible pts were aged ≥ 18 years, with β-thalassemia or hemoglobin (Hb) E/β-thalassemia (compound β-thalassemia mutation and/or multiplication of α-globin genes was allowed), requiring regular transfusions of 6-20 RBC units in the 24 weeks (wks) prior to randomization, with no transfusion-free period > 35 days. Pts were randomized 2:1 to luspatercept 1.0 mg/kg (up to 1.25 mg/kg allowed), or placebo, subcutaneously every 3 wks for ≥ 48 wks. Pts in both treatment arms continued RBC transfusions to maintain baseline Hb level and iron chelation therapy. Achievement and number of response episodes (defined as ≥ 33% reduction in RBC transfusion from baseline over any consecutive 24 wks) were assessed at a median follow-up of 64.1 wks. Duration of clinical benefit, defined as the time of first response (≥ 33% reduction in RBC transfusion over any 24 wks) to discontinuation due to any cause at that episode, was also assessed. Results:A total of 336 pts were randomized. In the ITT population, 224 pts in the luspatercept arm had a median baseline RBC transfusion burden in the 12 wks prior to randomization of 6.12 U RBCs (average 0.51 U/wk; range 3-14) and the 112 pts in the placebo arm had a median baseline transfusion burden of 6.27 U (average 0.52 U/wk; range 3-12). A total of 194 (57.7%) luspatercept and 65 (58%) placebo pts had prior splenectomy. As of the May 11, 2018 cutoff date, 92/224 (41.1%) luspatercept-treated pts and 3/112 (2.7%) placebo-treated pts had achieved ≥ 33% reduction in RBC transfusion over any 24 wks; of these luspatercept responders, 55 (59.8%) had ≥ 2 separate responses (over the treatment period up to data cutoff), 42 (45.7%) had ≥ 3, 29 (31.5%) had ≥ 4, and 19 (20.7%) had ≥ 5. Three (1.3%) pts receiving luspatercept re-responded at the same dose level after initially losing response. Median duration of clinical benefit (as defined above) for luspatercept responders was 53.5 wks (range 24-93.7). Forty-seven (21.0%) pts receiving luspatercept had no loss of response within the entire study period. Five luspatercept responders achieved RBC transfusion independence for ≥ 24 wks (median total duration was 60.1 wks) and 3 achieved RBC transfusion independence for ≥ 48 wks (median duration was 66 wks). The average number of RBC units saved over any 24 wks in all luspatercept responders was 6.55 U (0.27 U/wk) and was 8.16 U (0.34 U/wk) with transfusion burden > 15 U/24 wks, compared to baseline. As of the May 11, 2018 cutoff date, the safety population consisted of 243 pts (including 92 pts who crossed over from the placebo arm to the luspatercept arm). Frequent adverse events (AEs) in the luspatercept and placebo arms included bone pain (19.7% vs 8.3%, respectively), arthralgia (19.3% vs 11.9%), and dizziness (11.2% vs 4.6%). The safety profile for pts who crossed over from placebo to luspatercept was consistent with that observed for pts receiving luspatercept from baseline. The incidence of bone pain, arthralgia, and dizziness was largely non-severe grade 1-2, tended to decrease over time during the study, was not associated with dose level, and was not associated with treatment modification or discontinuation. Pts continue to be monitored for safety outcomes. Conclusions: Most β-thalassemia pts who were luspatercept responders experienced multiple response periods and had durable clinical benefit over the 64.1 wk follow-up period. The incidence of frequent AEs was consistent with the previously reported 48 wk safety profile for luspatercept, was not associated with dose level, and decreased over time with no impact on treatment modification or continuation. Disclosures Viprakasit: Celgene Corporation: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Protagonist: Consultancy, Research Funding; Vifor: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Ionis: Consultancy, Research Funding; La Jolla: Consultancy, Research Funding. Taher:Celgene Corporation: Research Funding; Protagonist Therapeutics: Consultancy, Research Funding; Abfero: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; La Jolla Pharmaceuticals: Consultancy, Research Funding; Ionis Pharmaceuticals: Consultancy. Hermine:AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. Porter:Vifor: Honoraria; Agios: Consultancy, Honoraria; Protagonist: Honoraria; La Jolla: Honoraria; Bluebird Bio: Consultancy, Honoraria; Celgene Corporation: Consultancy, Honoraria; Silence Therapeutics: Honoraria. Piga:Acceleron Pharma: Research Funding; Celgene Corporation: Consultancy, Research Funding; Novartis: Consultancy, Research Funding. Kuo:Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy; Celgene: Consultancy; Novartis: Consultancy, Honoraria; Pfizer: Consultancy. Coates:agios pharma: Consultancy, Honoraria; celgene: Consultancy, Honoraria, Other: steering committee of clinical study; apo pharma: Consultancy, Honoraria, Speakers Bureau; vifor: Consultancy, Honoraria. Voskaridou:Genesis: Consultancy, Research Funding; Protagonist: Research Funding; Celgene Corporation: Consultancy, Research Funding; Acceleron: Consultancy, Research Funding; Addmedica: Membership on an entity's Board of Directors or advisory committees. Perrotta:Acceleron Pharma: Research Funding; Novartis: Honoraria, Research Funding. Kattamis:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Apopharma: Honoraria; Vertex: Membership on an entity's Board of Directors or advisory committees; ViFOR: Membership on an entity's Board of Directors or advisory committees; Ionis: Membership on an entity's Board of Directors or advisory committees; Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Shetty:Celgene Corporation: Employment, Equity Ownership. Kuo:Celgene Corporation: Employment, Equity Ownership. Miteva:Celgene International: Employment. Zinger:Celgene Corporation: Employment. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Linde:Acceleron Pharma: Employment, Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership; Fibrogen, Inc.: Equity Ownership. Cappellini:CRISPR Therapeutics: Membership on an entity's Board of Directors or advisory committees; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Honoraria; Vifor Pharmaceutical: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

Context : FVIII is involved in the coagulation pathway. In the model developed by Hoffman in 1995, FVIII (with FIX) is at the center of coagulation. FVIII deficiency leads to a disease called hemophilia A. A deficiency of FVIII leads to inadequate coagulation and increases the risk of bleeding. Bleeding in hemophilic patient occurs mainly into large joints such as knee, elbow or ankle. Severe recurrence of hemarthrosis leads to irreversible arthropathy called hemophilic arthropathy (HA) characterized by a progressive complete destruction of the joint with permanent pain, musculoskeletal disability and poor quality of life. These patients have an increased inflammatory pattern. Prophylactic treatment of hemophilia A patients with the FVIII protein efficiently prevents bleeding events and preserves joint function. Recently, evidence for novel functions for FVIII across multiple systems, including the cardiovascular system, angiogenesis and maintenance of bone health has emerged. However, no study has shown the involvement of FVIII in inflammation. Here, we demonstrate that FVIII has an anti-inflammatory role and impacts the NF-κB pathway, independently from coagulation pathway. Materials and methods : Human fibroblast-like synoviocytes (FLS) were isolated from synovial tissues from five different HA patients and two non-HA patients at the time of knee or ankle joint arthroscopic synovectomy after informed consent. Primary FLS were used between the third and the ninth passage. We also used commercial normal and rheumatoid arthritis FLS, as well as THP-1. In particular, THP1-Blue NK-κB cells allow monitoring the NF-κB signaling transduction pathway. Different commercial recombinant FVIII were tested following dialysis. We are also tested recombinant FIX and vWF. FLS (5x105 cells) and THP1 (1x107 cells) were activated or not (medium) with LPS from Salmonella abortus equi (1 µg/mL) in the presence or absence of FVIII for 6 hr. Alternatively, THP1-Blue (5x105 cells) were activated or not (medium) with different PRR (Pattern Recognition Receptors) agonists for 24 hours: TLR2 (peptidoglycans), TLR4 (LPS) and TLR5 (flagellin). Cell supernatants were analyzed by ELISA and an ELISPOT were performed with a panel of 105 different cytokines. Results : Anti-inflammatory effect of FVIII After LPS stimulation and incubation with FVIII, cells expressed a unique profile of cytokine secretion, with a decrease in pro-inflammatory cytokines IL-1, IL-6 and TNF-alpha. This anti-inflammatory effect was not found when other coagulation factors, in particular vWF and FIX, were tested. A transcriptome analysis was performed on FLS from 3 different patients, normal FLS and THP1 cells and incubated alone or with FVIII. Transcriptomic results correlated with the inflammatory protein expression pattern, irrespective of the cell type. FVIII is involved in the NF- κ B signaling pathway through MYD88/TIRAP interaction Incubation of THP1 cells with the different TLR agonists resulted in an increase in the NF-KB signaling pathway. In the presence of FVIII, a decrease in NF-KB signaling was observed with TLR-2 and TLR-4 agonists but not with the TLR-5 agonist. NF-KB translocation in the nucleus, performed by AMNIS, was decreased when cells were incubated with FVIII (but not with vWF or FIX) after TLR-2/TLR-4 activation. Analysis of differences between TLR-2/TLR-4 and TLR-5 pathways showed that TIRAP is required only in TLR-2/TLR-4 to interact with MyD88 while TLR-5 pathway is required only for MyD88 activation. After silencing TIRAP by specific siRNA approach, no anti-inflammatory effect on NF-kB pathways was observed after FVIII incubation and TLR2/4 activation. Silencing TIRAP using specific siRNA abrogated the inhibitory effect of FVIII on TLR2/4-triggered NF-kB signaling. The results suggest that FVIII blocks the interaction between TIRAP and MyD88 and impairs the NF-kB pathway. In conclusion, our study suggests a new potential role for FVIII in the control of inflammation through the NF-kB pathway. Further investigations are ongoing with animal models to confirm these data and clinical study will be performed. Disclosures Hermine: AB science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding.

Compound AB8939 is a structurally novel, small chemical molecule, synthesized tubulin inhibitor that can circumvent two of the major resistance mechanisms in acute myeloid leukemia (AML), namely P-glycoprotein (Pgp) and myeloperoxidase (MPO) mediated resistance, thereby conferring an important advantage over traditional tubulin inhibitors. A series of ex vivo and in vivo studies provide proof-of-concept that AB8939 has broad anti-proliferative activity across the breath of acute myeloid leukemia (AML) subtypes, i.e. M0 through M7 of the French-American-British AML classification. Acute myeloid leukemia blasts were isolated from patients' peripheral blood and/or bone marrow samples, collected either at the time of diagnosis or following relapse, and also from patient derived xenograft (PDX) models. After purification, mononuclear cells were treated for 48 hours with various concentrations of AB8939 or cytarabine (Ara-C) and analyzed in a cell proliferation/viability assay. AB8939 produced a strong anti-proliferative action against blasts isolated from AML patients with a majority of IC50 values ranging from 1.4 nM to 1.0 µM. Two-thirds of AML patients had nanomolar sensitivity to AB8939 (IC50 ≤ 500 nM), while 44% where very sensitive (IC50 ≤ 100 nM) and 11% were highly sensitive (IC50 ≤ 10 nM). The potential of AB8939 to overcome Ara-C-resistance was also evident with 66% of Ara-C-resistant blasts (i.e. IC50 >5 µM) being sensitive to AB8939. Notably, AB8939 demonstrated activity across the entire spectrum of AML subtypes, according to the French-American-British (FAB) AML classification, with an IC50 of < 50 nM in M0, M1, M4, M5 and M6 subtypes, corresponding to over 90% of the AML patient population. A slightly lower sensitivity was observed for the M3 subtype (IC50 = 1.25 µM). Additionally, potent AB8939 activity was also seen in Ara-C-insensitive biphenotypic and mixed-phenotype acute leukemia samples. All FAB categories other than M7 were tested in the abovementioned ex vivo assessment. Acute megakaryocytic leukemia (FAB AML subtype M7) is a rare form of adult AML, accounting for only 1% of cases, and is associated with resistance to standard treatment and poor prognosis. The effect of AB8939 in this subtype was assessed in vivo using an AMKL26 model, an NSG mouse model based on cells isolated from a patient with an aggressive acute megakaryocytic leukemia presenting the ETO2-GLIS2 fusion oncogene. Following post graft detection of blasts, single agent AB8939 was administered intravenously at a dose of 2 mg/kg for three consecutive days per week (3 ON / 4 OFF) for 2 weeks and then at 5 mg/kg for three consecutive days per week (3 ON / 4 OFF) for 1 week. At the end of the 3-week treatment period, blast detection in bone marrow was performed via bioluminescence imaging with comparison to vehicle-treated controls. As seen in the figure below, single agent AB8939 showed strong anti-leukemic activity in this AMKL26 mouse model as evidenced by the near eradication of blasts. No blasts could be detected in 6 out of 8 mice treated with AB8939. At the described dosing schedule, AB8939 was well-tolerated with no toxicity-related deaths and no impact on animal body weight or behavior. These findings provide preclinical proof of concept for the development of AB8939 as a next-generation tubulin inhibitor for AML, in particular for poor-prognosis AML subsets and relapse/refractory AML; i.e. patients that currently have very limited therapeutic options and represent the highest unmet medical need. Disclosures Goubard: AB Science: Employment. Humbert:AB Science: Employment. Mansfield:AB Science: Employment, Patents & Royalties. Hermine:AB Science: Membership on an entity's Board of Directors or advisory committees. AB8939 Study Group:AB Science: Consultancy, Employment.

Purpose Equilibrium between red blood cells (RBC) production and clearance maintains an appropriate circulating RBC biomass. During anemia or hypoxia, a well-characterized hypoxia-dependent induction of erythropoietin (EPO) synthesis leads to an increase in RBC production. At the other extremity of the RBC lifespan, age-related modifications of RBC properties are expected to be recognized by the mononuclear phagocytic system (MPS) and trigger their clearance. We reasoned that, like RBC production, RBC clearance might be physiologically regulated by hypoxia and therefore that its downregulation could contribute to maintain an appropriate RBC biomass. A mouse model was used to explore specific hypotheses on potential regulatory mechanisms involved in RBC clearance. Material and methods Two steps in vivo biotinylation was used to evaluate the impact of EPO on 3 RBC subpopulations: a young subpopulation ( 34 days at treatment initiation) that is steadily cleared. A model of RBC banking (leucocyte depleted and stored in CPDA solution) was used to evaluate the clearance after transfusion of fluorescently-labeled storage-damaged RBC by flow cytometry. Different recipient models were used to evaluate the impact of specific parameters on RBC clearance including: phlebotomy-induced anemia, normobaric hypoxia, erythropoiesis-stimulating agent (ESA) treatment (darbepoietin), splenectomy, doxorubicin-induced inhibition of erythropoiesis and EPO neutralization (anti-EPO rabbit serum) either alone or in combination. Results Decreased clearance of the oldest subpopulation was observed 2 days after ESA treatment and before the increase in RBC production (7 days). After 20 days of treatment, an increased number of RBC from the oldest subpopulation was detected in circulation confirming that senescent RBC clearance is sensitive to EPO signaling. After transfusion, clearance of storage-damaged RBC is reduced by 30% in anemic recipients when compared to non-anemic recipients. RBC clearance is significantly reduced in hypoxic non-anemic recipients, as soon as 6 hours after the initiation of hypoxia, suggesting that hematocrit per se does not affect RBC clearance. In ESA-treated non-anemic non-hypoxic mice, RBC clearance is also reduced showing that EPO signaling is sufficient. To investigate the role of the spleen in this process, splenectomy was combined with the previous models. As expected, RBC clearance was reduced by 20% in splenectomized recipients. RBC clearance is however even more decreased when splenectomy is combined with anemia, hypoxia or ESA treatment compared to splenectomized or control mice, suggesting that EPO downregulation of RBC clearance is not restricted to the spleen. Erythropoiesis inhibition did not alter the anemia-induced downregulation of RBC clearance ruling out the possibility that an erythroid factor is involved in the process. Finally, neutralization of circulating EPO not only abolishes the reduction of RBC clearance observed in anemic recipients, but also increases RBC clearance in both anemic and non-anemic recipients. Taken together these results indicate that EPO regulates RBC clearance during anemia and in steady state (Figure). Conclusion RBC clearance is downregulated during anemia/hypoxia and EPO is sufficient and necessary to mediate this physiological function. RBC clearance downregulation preceded the increase in production rate induced by ESA treatment suggesting it is a very early physiological response to maintain oxygen supply during anemia. The lifespan of a circulating RBC is therefore adaptable and could be regulated by 2 factors: the RBC pro- and anti-phagocytic properties on one side and, on the other side, the MPS level of activity and sensitivity toward these RBC properties. In case of anemia or hypoxia, increased EPO level would act on the RBC itself, on the activity/sensitivity of the MPS or both to downregulate RBC clearance until the equilibrium between oxygen need and supply is restored. Future studies will evaluate if the pathological dysregulation of this mechanism participates in the pathogenesis of anemia or, modulate transfusion efficacy and burden in chronically transfused patients. Figure Disclosures Buffet: Zimmer Biomet: Research Funding. Hermine:Celgene: Research Funding; Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding. Amireault:Zimmer Biomet: Research Funding.