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SF3B1, SRSF2, and U2AF1 are the most frequently mutated splicing factor genes in the myelodysplastic syndromes (MDS). We have performed a comprehensive and systematic analysis to determine the effect of these commonly mutated splicing factors on pre-mRNA splicing in the bone marrow stem/progenitor cells and in the erythroid and myeloid precursors in splicing factor mutant MDS. Using RNA-seq, we determined the aberrantly spliced genes and dysregulated pathways in CD34+ cells of 84 patients with MDS. Splicing factor mutations result in different alterations in splicing and largely affect different genes, but these converge in common dysregulated pathways and cellular processes, focused on RNA splicing, protein synthesis, and mitochondrial dysfunction, suggesting common mechanisms of action in MDS. Many of these dysregulated pathways and cellular processes can be linked to the known disease pathophysiology associated with splicing factor mutations in MDS, whereas several others have not been previously associated with MDS, such as sirtuin signaling. We identified aberrantly spliced events associated with clinical variables, and isoforms that independently predict survival in MDS and implicate dysregulation of focal adhesion and extracellular exosomes as drivers of poor survival. Aberrantly spliced genes and dysregulated pathways were identified in the MDS-affected lineages in splicing factor mutant MDS. Functional studies demonstrated that knockdown of the mitosis regulators SEPT2 and AKAP8, aberrantly spliced target genes of SF3B1 and SRSF2 mutations, respectively, led to impaired erythroid cell growth and differentiation. This study illuminates the effect of the common spliceosome mutations on the MDS phenotype and provides novel insights into disease pathophysiology.

Background: Endothelial dysfunction underlies the two main complications of chimeric antigen receptor T (CAR-T) cell therapy, i.e. cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). The purpose of this retrospective analysis was to evaluate and validate the Endothelial Activation and Stress Index (EASIX)) as predictor for CRS and ICANS in patients receiving CD19-directed CAR-T cells. Methods: In this retrospective study, the training cohort recruited 107 patients treated with CAR-T cells at the University Hospital Heidelberg (n=83) and Charité University Medicine Berlin (n=24) from Oct 1, 2018, to March 31, 2021. Patients from the validation cohort (n=93) received CAR-T cells within the ZUMA-1 trial (ClinicalTrials.gov number: NCT02348216). The training cohort included 37 and 34 patients with relapsed / refractory (r/r) large B-cell lymphoma (LBCL) treated with Axi-cel and Tisa-cel, respectively, 1 patient with acute lymphoblastic leukemia (ALL) treated with Tisa-cel, 2 patients with mantle cell lymphoma (MCL) treated with KTE-X19 on an early access program; and 5 patients with LBCL, 5 patients with MCL, 5 patients with chronic lymphocytic leukemia, 4 patients with follicular lymphoma, and 14 patients with ALL treated with the 3 rd generation CAR-T HD-CAR-1. Median age was 57 (20-81) years, 72% were male. The 93 patients of the validation cohort all had r/r LBCL and received Axi-Cel. EASIX and serum levels of endothelial stress markers (angiopoietin-2, suppressor of tumorigenicity-2, soluble thrombomodulin and interleukin-8) were measured before start of lymphodepletion (EASIX-pre), and on days 0, 3, and 7 after CAR-T infusion. Primary endpoints were severe CRS and/or ICANS (grades 3-4). Results: Of the 107 patients of the training cohort, 61 patients (58%) developed CRS grades 1-4 and 24 patients (22%) developed ICANS grades 1-4. Higher grade CRS (grade ≥ 3) was seen in 6 patients (6%) with a median onset of 4 (0-14) days, while grade ≥ 3 ICANS occurred in 11 patients (11%; median onset 8 (4-17) days). EASIX values increased continuously from lymphodepletion to day 7 after CAR-T cell application (EASIX-pre 2.0 (0.5-76.6, interquartile range (IQR) 1.2/4.1); EASIX-d0 2.0 (0.3-91.5, IQR 1.2/4.2); EASIX-d3 2.4 (0.3-69.1, IQR 1.3/4.9) and EASIX-d7 2.7 (0.4-94.0, IQR 1.4/7.5)). In the validation cohort, Grade ≥ 3 CRS was observed in 10 patients (11%) and grade ≥ 3 ICANS in 28 patients (30%). Similar to the training cohort, EASIX values rose from lymphodepletion to day 3 after CAR-T cell application (EASIX-pre 1.8 (0.3-106.1, IQR 1.0/4.7); EASIX-d0 2.0 (0.3-120.4, IQR 1.1/4.1) and EASIX-d3 2.7 (0.3-57.9, IQR 1.7/6.2). In both cohorts, all EASIX values (pre, d0, d3, d7) were significantly higher in patients who developed either grade 3-4 CRS, ICANS or both (see Figure 1 for the training cohort). EASIX predicted grade 3-4 CRS and ICANS before lymphodepleting therapy (-pre), on day 0 and on day 3 in both cohorts: AUC EASIX-pre, training cohort 0.73 (0.62-0.85, p=0.002), validation cohort 0.76 (0.66-0.87, p Serum endothelial stress markers did not predict the two complications when assessed before CAR-T infusion, but diagnostic markers were strongly associated with CRS and ICANS grade 3-4 on day+7. Conclusions: EASIX-pre is a validated predictor of severe complications after CAR-T therapy and may help to tailor safety monitoring measures according to the individual patient's needs. Data on patients from the ZUMA-1 trial were provided by Kite/Gilead. Figure 1 Figure 1. Disclosures Penack: Astellas: Honoraria; Gilead: Honoraria; Jazz: Honoraria; MSD: Honoraria; Novartis: Honoraria; Neovii: Honoraria; Pfizer: Honoraria; Therakos: Honoraria; Takeda: Research Funding; Incyte: Research Funding; Priothera: Consultancy; Shionogi: Consultancy; Omeros: Consultancy. Schmitt: MSD: Membership on an entity's Board of Directors or advisory committees; Apogenix: Research Funding; Hexal: Other: Travel grants, Research Funding; TolerogenixX: Current holder of individual stocks in a privately-held company; Kite Gilead: Other: Travel grants; Bluebird Bio: Other: Travel grants; Novartis: Other: Travel grants, Research Funding. Müller-Tidow: Janssen: Consultancy, Research Funding; Pfizer: Research Funding; Bioline: Research Funding. Bullinger: Pfizer: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Astellas: Honoraria; Menarini: Consultancy; Sanofi: Honoraria; Novartis: Consultancy, Honoraria; Seattle Genetics: Honoraria; Amgen: Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Bayer: Research Funding; Daiichi Sankyo: Consultancy, Honoraria; Gilead: Consultancy; Hexal: Consultancy; Janssen: Consultancy, Honoraria; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding. Dreger: Gilead Sciences: Consultancy, Speakers Bureau; AbbVie: Consultancy, Speakers Bureau; Janssen: Consultancy; Novartis: Consultancy, Speakers Bureau; BMS: Consultancy; Bluebird Bio: Consultancy; AstraZeneca: Consultancy, Speakers Bureau; Riemser: Consultancy, Research Funding, Speakers Bureau; Roche: Consultancy, Speakers Bureau.

Purpose: Endothelial complications are principal causes of non-relapse mortality (NRM) after allogeneic stem cell transplantation (alloSCT). Sepsis is a dysfunctional endothelial response to harmful microorganisms with increased risk of microvascular damage and organ failure. We hypothesized that the endothelial activation and stress index (EASIX) predicts risk of sepsis after alloSCT. Methods: In this retrospective evaluation, 1290 patients (random 1:1 allocation into a training cohort and a validation cohort while balancing for sepsis events) were assessed for presence of neutropenic fever, sepsis and infectious pathogens within 50 days after alloSCT. Sepsis and septic shock were defined according to the modified Sepsis-3 guidelines by the Infectious Diseases Working Party (AGIHO) and Intensive Care Working Party (iCHOP) of the German Society of Hematology and Medical Oncology (DGHO) for neutropenic cancer patients. EASIX and additional serum markers were assessed longitudinally before and after transplantation and correlated with outcome. Established clinical risk scores (EBMT, HCT-CI and VOD-CIBMTR) were raised and compared to EASIX. Results: Within the full cohort of 1290 patients transplanted since 01/2004, neutropenic fever episodes until day+50 after alloSCT were reported in 989 (76.7%), sepsis in 93 (7.2%), catecholamine use in 35 (2.7%), and mechanical ventilation in 31 (2.4%) patients. Patients who developed sepsis until day+50 differed from patients without early sepsis in more frequently having a higher disease score (58% vs 33%, p Prior to conditioning therapy, EASIX(-pre) was the only marker to predict the hazard of early sepsis irrespective of pathogen detection in time-dependent ROC (AUC 0.85 at day 50) and multivariable cause-specific Cox regression analyses (HR per two-fold increase 2.3 (1.9-2.8, p Pre-conditioning leukocyte counts, CRP or endothelial serum markers did not associate with early sepsis. After transplantation starting with day 0, sepsis associated with EASIX at any time point until day+28, and in addition with suppressor of tumorigenicity (ST)2 and interleukin-18. Conclusions: EASIX is a powerful predictor of early sepsis and 6-months NRM, irrespective of detected pathogens. Patients with EASIX-pre>2.32 represent a high-risk cohort requiring intensive prophylaxis and endothelial protective treatment strategies. Figure 1 Figure 1. Disclosures Schönland: Pfizer: Honoraria; Janssen: Honoraria, Other: Travel grants, Research Funding; Prothena: Honoraria, Other: Travel grants; Sanofi: Research Funding; Takeda: Honoraria, Other: Travel grants. Hegenbart: Pfizer: Consultancy, Honoraria; Janssen: Consultancy, Research Funding; Alnylam: Honoraria; Akcea: Honoraria; Prothena: Research Funding. Schmitt: Apogenix: Research Funding; Hexal: Other: Travel grants, Research Funding; Novartis: Other: Travel grants, Research Funding; Kite Gilead: Other: Travel grants; Bluebird Bio: Other: Travel grants; MSD: Membership on an entity's Board of Directors or advisory committees; TolerogenixX: Current holder of individual stocks in a privately-held company. Dreger: Novartis: Consultancy, Speakers Bureau; Bluebird Bio: Consultancy; Janssen: Consultancy; Gilead Sciences: Consultancy, Speakers Bureau; BMS: Consultancy; AbbVie: Consultancy, Speakers Bureau; AstraZeneca: Consultancy, Speakers Bureau; Riemser: Consultancy, Research Funding, Speakers Bureau; Roche: Consultancy, Speakers Bureau.

In patients with steroid-refractory/resistant graft-versus-host disease (GvHD), extracorporeal photopheresis (ECP) has been identified as a promising therapeutic strategy due to its safety profile and convincing clinical response rates. While previous studies have reported on the role of Th1, Th2 and Treg cells in ECP therapy, further comprehensive analysis of T helper cells is necessary to provide better understanding of the underlying mechanisms. In this study, we thus investigated the influence of long-term ECP treatment on both Th cells as well as on immune checkpoint molecules and apoptosis. Overall, we investigated 27 patients with GvHD treated by ECP therapy, containing 13 patients with acute GvHD and 14 patients with chronic GvHD. 10/13 (76.9%) of aGvHD and 9/14 (64.3%) of cGvHD patients clinically responded to ECP therapy. Three (23.1%) patients reached CR and seven (53.8%) patients achieved PR under ECP treatment in patients with aGvHD, while in patients with cGvHD CR was achieved in one (7.1%) and PR in eight (57.1%) patients. Stabilization of disease was observed in five (35.7%) patients. On an immunological level, aGvHD, cGvHD and healthy donors (HD) patients showed different profiles of Th populations. In GvHD patients, significantly higher levels for Th2 (aGvHD vs. HD: 36.26% vs. 13.88%, p = 0.014; cGvHD vs. HD: 30.71% vs. 13.88%, p = 0.026), Th17 (aGvHD vs. HD: 19.21% vs. 7.49%, p = 0.038), Th22 (aGvHD vs. HD: 1.22% vs. 0.11%，p = 0.011; cGvHD vs. HD: 0.64% vs. 0.11%, p = 0.012) and GM-CSF + Th cells (aGvHD vs. HD: 1.15% vs. 0.14%, p = 0.022; cGvHD vs. HD: 0.84% vs. 0.14%，p = 0.012) and clearly lower levels for T follicular helper (Tfh) cells including Th1- (aGvHD vs. HD: 0.37% vs. 2.04%, p = 0.002; cGvHD vs. HD: 1.28% vs. 2.04%, p = 0.03) and Th2-like cells (aGvHD vs. HD: 1.17% vs. 4.19%, p = 0.033) were observed in comparison to HDs. This suggests Th cells account for a crucial role in GvHD pathogenesis. ECP therapy was able to accelerate recovery of Tfh cells, including Th1- (Time point 1 vs. Time point 2 in aGvHD: 0.37% vs. 0.97%, p = 0.028), Th2- (T1 vs. T2 in aGvHD: 1.17% vs. 1.35%, p = 0.049; T1 vs. T2 in cGvHD: 2.08% vs. 3.15%, p = 0.048) and Th17-like Tfh cells (T1 vs. T2 in aGvHD: 1.82% vs. 2.70%, p = 0.034), facilitating immune reconstitution after allo-HSCT and thereby alleviating GvHD. Clinical response in aGvHD patients was strongly associated with elevation of Th22 cells by ECP therapy showing 51% upregulation (T1 vs. T2: 0.86% vs. 1.3%，p=0.007). In addition, we also found that the expression of the Fas receptor on effector T cells could be further upregulated with ECP treatment (T1 vs. T2 in cGvHD: 49.65% vs. 56.46%, p = 0.011), which increases the susceptibility of these effectors T cells to Fas-mediated apoptosis. This could lead to the elimination of these overactivated effector T cells and the perseverance of immunological tolerance by triggering activation-induced cell death. In addition, a reduction of Tim-3-expressing effector T cells, which are associated with the severity of GvHD, with ECP therapy (T1 vs. T2 for aGvHD: 18.09% vs. 15.10%, p = 0.044) was discovered. In conclusion, ECP therapy exerts immunomodulatory effects by promoting balanced immune reconstitution and inducing immune tolerance, making it an attractive and promising treatment option for patients with GvHD. Disclosures Schubert: Gilead: Consultancy. Hegenbart: Alnylam: Honoraria; Akcea: Honoraria; Janssen: Consultancy, Research Funding; Prothena: Research Funding; Pfizer: Consultancy, Honoraria. Schönland: Prothena: Honoraria, Other: Travel grants; Takeda: Honoraria, Other: Travel grants; Pfizer: Honoraria; Janssen: Honoraria, Other: Travel grants, Research Funding; Sanofi: Research Funding. Müller-Tidow: Pfizer: Research Funding; Bioline: Research Funding; Janssen: Consultancy, Research Funding. Dreger: Riemser: Consultancy, Research Funding, Speakers Bureau; Bluebird Bio: Consultancy; Roche: Consultancy, Speakers Bureau; AbbVie: Consultancy, Speakers Bureau; BMS: Consultancy; AstraZeneca: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Janssen: Consultancy; Gilead Sciences: Consultancy, Speakers Bureau. Schmitt: MSD: Membership on an entity's Board of Directors or advisory committees; Hexal: Other: Travel grants, Research Funding; Kite Gilead: Other: Travel grants; TolerogenixX: Current holder of individual stocks in a privately-held company; Bluebird Bio: Other: Travel grants; Novartis: Other: Travel grants, Research Funding; Apogenix: Research Funding. Schmitt: Therakos/Mallinckrodt: Research Funding; TolerogenixX Ltd: Current Employment; Jazz Pharmaceuticals: Other: Travel grant; Hexal: Other: Travel grant.

Background: Fibrosing chronic graft-versus-host disease (cGVHD) is a debilitating complication after allogeneic stem cell transplantation (allo-SCT), and its pathophysiology is poorly understood. Kynurenine and its metabolites were shown to associate with both, interferon-gamma (IFNg) activation and fibrosis. This study investigates the interplay between members of the IFNγ pathway and Kynurenin-derived metabolites in cGVHD. Methods: Using a liquid chromatography tandem mass spectrometry approach on sera obtained on day+100 (n=430) and/or at onset of cGVHD symptoms (n=196) of our prospectively collected biobank after alloSCT, we measured concentrations of Kyn pathway metabolites (kynurenin (Kyn), anthranilic acid (AA), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), and 3-hydroxy-anthranilic acid (3-HAA). We also measured C-X-C chemokine ligand 9 (CXCL9), interleukin (IL-)18, tryptophane (Trp) and indoleamine-2,3-dioxygenase (IDO) by ELISA. Results: We observed increased CXCL9 and IDO levels, and increased activity of the Kynurenine pathway in both non-severe and severe cGVHD. Interestingly, severe fibrosing cGVHD differed from any other form of cGVHD in a significant pathway shift toward AA and KA. This resulted in a reduced 3-HAA/AA ratio. A score consisting of low 3-HAA/AA ratio and high KA serum levels at onset of mild cGVHD symptoms predicted risk specifically of severe fibrosing cGVHD. This altered pathway in severe fibrosing cGVHD correlated with reduced activity of the Vitamin-B2-dependent kynurenine monooxygenase, low vitamin B6, and increased interleukin-18. Our results are consistent with a triple-hit model for fibrosing cGVHD including low activity of kynurenine monooxygenase (KMO, Vitamin B2 and B6 dependent) in the context of high IL18 serum levels and CXCL9-induced IDO activation (Figure 1). Conclusion: Chronic GVHD associates with an IFNg signature and increased activity of the Kynurenin pathway. KA and 3-HAA/AA defined the first molecular distinction between fibrosing and non-fibrosing cGVHD. The mechanism may involve Vitamin B2/B6 deficiency, and high CXCL9 and IL18. The Kyn metabolite signature is a candidate biomarker for severe fibrosing cGHVD and provides a rationale for translational trials on prophylactic Vitamin B2/B6 supplementation for cGVHD prevention. Figure 1: Triple hit model of fibrosing cGVHD (Hypothesis): Severe fibrosing cGVHD associates with a strong CXCL9-induced activation of IDO. The result of this activation is influenced by a reduced activity of kynurenine monooxygenase (KMO), either due to genetic polymorphisms or lack of Vitamin B2, and further aggravated by lack of Vitamin B6. The resulting metabolic deviation increases AA concentrations and reduces the 3-HAA/AA ratio. Finally, high IL-18 associates with increased serum KA. These three hits result in a metabolic situation with high KA and a low ratio 3-HAA/AA that predicts risk of fibrosing cGVHD. Figure 1 Figure 1. Disclosures Mueller-Tidow: Janssen Cilag: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Bioline: Consultancy, Research Funding.

BACKGROUND: In a previous study we have shown that CD19-directed chimeric antigen receptor (CAR)-T cells do not appear to be inferior to alloHCT when used as standard cellular immunotherapy (CI) for patients with multiply r/r LBCL (EBMT 2020). The purpose of the present follow-up analysis was to further compare the risk profile of the 2 cohorts by applying the EASIX score (lactate dehydrogenase (U/L) × creatinine (mg/dL)/thrombocytes (109 cells per L)), and to assess if EASIX could be used as outcome predictor in patients with r/r LBCL undergoing CAR-T and alloHCT, respectively. METHODS: Eligible were all patients referred to our institution with relapsed/refractory (R/R) DLBCL and a tumor board decision recommending treatment with CAR-T cells between 07/2018 and 02/2020 and those recommending allogeneic donor search between 2004 and 2019. Patients with DLBCL transformed from CLL were excluded. EASIX was evaluated retrospectively using uni- and multivariable analyses (with regards to age, gender and number of failed therapy lines) and mortality using Cox regression analyses. RESULTS: 41 patients intended for CAR-T cells and 60 patients intended for alloHCT were included. In both cohorts nearly all patients had active disease at indication. Cohorts were comparable for sex, time from diagnosis, ZUMA1 eligibility, and PS, but CAR-T patients tended to be older (median 56 vs 51 years, p=0.093), and had more often primary refractory and bulky disease (p=0.004 and p=0.04, respectively). Median EASIX score across both cohorts was 1.50 (0.27-70.5), with significantly higher scores in the CART group both at indication (EASIX-ind; median 1.79 and 1.22 for CAR-T and alloHCT, respectively, p=0.031) and at conditioning for CI (EASIX-pre, median 2.24 vs 1.26, p=0.005). Median OS from indication was 475d for the CAR-T cohort vs 285d for the alloHCT cohort (p=0.88). On multivariate analysis, EASIX-ind was significantly associated with adverse OS if alloHCT was intended (HR per 2fold increase 1.43, 95%CI 1.08-1.90, p=0.013), but not if CAR-T was intended (HR per 2fold increase 1.16, 95%CI 0.88-1.53, p=0.3). After CI, 12-month estimates for NRM, relapse incidence, PFS, and OS for CAR-T vs alloHCT were 3% vs 21% (p=0.04), 59% vs 44% (p=0.12), 39% vs 33% (p=0.97), and 68% vs 54% (p=0.32). EASIX-pre predicted overall survival (OS) in both CAR-T (HR per 2fold increase 2.11, 95%CI 1.21-3.7, p=0.009) and alloHCT (HR per 2fold increase 3.69, 95%CI 1.54-8.31, p=0.003) cohorts. In the alloHCT group, the EASIX effect was largely driven by higher NRM risk with increasing EASIX-pre, while in the CAR-T group poorer OS with increasing EASIX-pre was largely relapse-related. CONCLUSIONS: In patients undergoing CI for r/r LBCL, EASIX measured prior to conditioning can predict mortality after both CAR-T and alloHCT. If applied already at indication for CI, the predictive capacity of EASIX is weaker and no longer significant if CAR-T is intended. Further studies for validation of this data appear to be warrantable. Disclosures Schmitt: MSD: Membership on an entity's Board of Directors or advisory committees, Other: PI of clinical trials on letermovir; TolerogenixX Ltd: Other: Co-Founder and shareholder; Hexal: Other: Travel grants , Research Funding; Apogenix: Research Funding; Kite: Other: Travel grants, educational activities and conferences; Novartis: Other: educational activities and conferences, Research Funding. Dietrich:Roche: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; KITE: Membership on an entity's Board of Directors or advisory committees. Schmitt:Hexal: Other: Travel grants ; TolerogenixX LtD: Other: Co-founder, Part-time employee ; Therakos/Mallinckrodt: Research Funding; Jazz Pharmaceuticals: Other: Travel grants . Dreger:Neovii: Research Funding; Roche: Consultancy, Speakers Bureau; Riemser: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Janssen: Consultancy; Gilead: Consultancy, Speakers Bureau; AstraZeneca: Consultancy; AbbVie: Consultancy, Speakers Bureau.

Background: Hyperbilirubinemia occurs frequently in the early phase after allogeneic stem cell transplantation (alloSCT). In the present study we analysed whether high bilirubin levels until day +28 after alloSCT are associated with clinical outcome independent of liver toxicity and clinically defined diseases, such as sinusoidal obstruction syndrome (SOS/VOD), transplantation-associated thrombotic microangiopathy (TAM) or steroid-refractory acute graft-versus-host disease (refrGVHD). Methods: Serum bilirubin levels from 901 patients (training cohort) and from 399 patients transplanted in an independent institution (validation cohort), obtained over the first 4 weeks following alloSCT, were analyzed along with routine serum markers for liver cell and cholangiocyte damage (alanine transaminase, ALT, gamma-glutamyltransferase, gGT), and with markers of endothelial dysfunction, such as Angiopoietin-2 serum levels and the endothelial activation and stress index before conditioning therapy (EASIX-pre) and on the day of transplantation (EASIX-d0). Finally, we analysed the impact of prophylaxis with the endothelium-protective agents pravastatin and ursodeoxycholic acid (UDA) on early bilirubinaemia. Results: Maximum bilirubin levels (days 0-28) were associated with increased risk of overall mortality (OM) and non-relapse mortality (NRM) in patients without SOS/VOD. The optimal bilirubin cut-off for prediction of NRM was found at 3.6 mg/dl (61.6 mM), so that any event of bilirubin≧3.6 mg/dl between days 0 and 28 was defined as early hyperbilirubinemia (EABI). Independent of SOS/VOD, refrGVHD or TAM, EABI predicted OM and NRM in the training and the validation cohort. Although EABI occurred more frequently after anti-thymocyte globulin (ATG) treatment and in patients with myelofibrosis, the effect of EABI on NRM remained stable irrespective of these conditions. EABI was not associated with markers of liver cell and cholangiocyte damage. In contrast, EABI was significantly correlated with pre-transplant serum levels of Angiopoietin-2 as well as increased EASIX-pre and EASIX-d0. Patients receiving prophylaxis with pravastatin and UDA had a reduced risk of death after EABI. Conclusion: EABI is a predictor of NRM and OM independent from SOS/VOD, refrGVHD and TAM. The association of EABI with EASIX, Angiopoietin-2 and statin/UDCA prophylaxis, but not with liver enzymes, suggests a mechanistic role of the endothelium for the pathophysiology of EABI. Table 1: Multivariable Cox-Regression with endpoint non-relapse mortality after d+28. VOD patients were excluded from this analysis. p-values of the training cohort were corrected by bootstrap 1000. Table 1 Disclosures Luft: Neovii: Research Funding; JAZZ: Research Funding. Bullinger:Bayer: Other: Financing of scientific research; Amgen: Honoraria; Astellas: Honoraria; Sanofi: Honoraria; Seattle Genetics: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Daiichi Sankyo: Honoraria; Gilead: Honoraria; Hexal: Honoraria; Janssen: Honoraria; Jazz Pharmaceuticals: Honoraria; Menarini: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; Abbvie: Honoraria. Dreger:Neovii, Riemser: Research Funding; MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; AbbVie, AstraZeneca, Gilead, Janssen, Novartis, Riemser, Roche: Consultancy; AbbVie, Gilead, Novartis, Riemser, Roche: Speakers Bureau.

Introduction Patients with myelodysplastic syndromes (MDS) are at risk of early death from cardiovascular complications due to the link between clonal hematopoiesis and endothelial dysfunction. EASIX (Endothelial Activation and Stress Index) has been established to predict endothelial complications after allogeneic stem cell transplantation (alloSCT). EASIX is an endothelial dysfunction related biomarker that can be easily obtained with routine laboratory markers (creatinine× LDH/thrombocytes). We analyzed whether EASIX can predict mortality in higher-risk and in lower-risk MDS patients. Since alloSCT can alter the natural history of MDS and may be an independent contributor to endothelial complications, this analysis was restricted to patients who did not undergo alloSCT during the course of their disease. Patients and Methods We investigated the impact of EASIX measured at first diagnosis on survival of patients with lower- and higher-risk MDS (no allogeneic transplantation) in two independent institutions: n=192 (training cohort) and n=333 (validation cohort). For the purposes of this study, patients with low and intermediate-1 according to IPSS and very low and low-risk according to IPSS-R, respectively, were considered to have lower-risk MDS, while patients with intermediate-2 and high-risk according to IPSS and intermediate, high and very-high according to IPSS-R, respectively, were considered to have higher-risk MDS. Serum markers of endothelial cell distress were measured and correlated to EASIX. Results While no effects of EASIX on survival were observed in higher-risk patients, EASIX was associated with shorter survival in patients with lower-risk MDS in both cohorts (univariate: training cohort: hazard ratio (HR): 1.46; 95% confidence interval (CI) 1.24-1.71; p-value < 0.001 / validation cohort: HR 1.31 [1.17-1.48]; p-value < 0.001). We visualized this continuous effect of EASIX in lower-risk disease by grouping patients into quartiles according to EASIX (Figure 1 A and B). In both cohorts, patients in the highest quartile had a shorter survival compared to patients in lower quartiles. Confining our analysis to lower-risk patients who did not develop AML within the observation period, EASIX similarly predicted OS in both cohorts (training: n=78, no. of events n=17, HR per log2 increase 1.43 [1.05-1.94]; p=0.02; validation: n=267, no. of events n=93, HR per log2 increase 1.33 [1.21-1.47]; p Conclusion We introduce EASIX as an easily accessible and independent predictor for survival in patients with lower-risk MDS. The strong correlation of EASIX and ANG2 underlines the endothelial nature of this biomarker. Disclosures Germing: Celgene: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Jazz Pharmaceuticals: Honoraria; Amgen: Honoraria. Kobbe:Neovii: Honoraria, Other: Travel support; Pfizer: Honoraria, Other: Travel support; Medac: Honoraria, Other: Travel support; Abbvie: Honoraria, Other: Travel support; Biotest: Honoraria, Other: Travel support; Jazz: Honoraria, Other: Travel support; Celgene: Honoraria, Other: Travel support, Research Funding; Roche: Honoraria, Other: Travel support; Amgen: Honoraria, Other: Travel support, Research Funding; MSD: Honoraria, Other: Travel support; Novartis: Honoraria, Other: Travel support; Takeda: Honoraria, Other: Travel support. Kaivers:Jazz Pharmaceuticals: Other: Travel Support. Merz:Janssen: Other: Travel grants; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: Travel grants; Abbvie: Other: Travel grants; Celgene: Other: Travel grants; Takeda Vertrieb GmbH: Other: Travel grants, Research Funding. Dreger:MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; Neovii, Riemser: Research Funding; AbbVie, Gilead, Novartis, Riemser, Roche: Speakers Bureau; AbbVie, AstraZeneca, Gilead, Janssen, Novartis, Riemser, Roche: Consultancy.

Background: Morbidity and mortality after allogeneic hematopoietic cell transplantation (alloHCT) are still essentially affected by reactivation of cytomegalovirus (CMV). Letermovir is the first drug approved for prophylaxis of CMV reactivation in seropositive patients who have undergone alloHCT. Letermovir shows neither myelo- nor nephrotoxicity, and significantly reduced the incidence of CMV reactivation in a pivotal phase III trial (NEJM 2017;377:2433). Therefore, we have adopted letermovir prophylaxis according to the label as standard policy in our institution in March 2018: in seropositive recipients letermovir is given from engraftment until day +100 or CMV reactivation. The purpose of this study was to investigate if the positive trial results could be reproduced under real-world conditions. Methods: The study cohort contained the first seropositive 82 patients who received letermovir prophylaxis at our institution (between March 2018 and March 2019). These were compared with a control cohort comprising another 82 patients who underwent alloHCT at our institution between January 2017 and March 2018 immediately before the introduction of letermovir. Quantitative PCR was used to monitor CMV viremia twice a week during the inpatient period and weekly thereafter. Patients reactivating CMV prior to engraftment were not considered as event in both groups. Results: Both cohorts were matched for underlying disease, CMV donor/recipient sero-status, use of ATG, and donor type. No higher grade adverse effects of letermovir intake were observed. With altogether 11 reactivation events, the cumulative incidence of CMV reactivation on day +100 was 13% (95%CI 6-21%) in the letermovir cohort which was significantly lower than in the control group (34 events, d +100 cumulative incidence 41% (95%CI 31-52%); HR 0.32 (95%CI 0.24-0.44); p Conclusions: This observational study proves in a real-world setting the efficacy and safety of letermovir for the prophylaxis of CMV reactivation after alloHCT. Letermovir lowered the incidence of CMV reactivation to the same extent as observed in the approval trial. In terms of health economics, letermovir reduced hospitalization needs and costs for therapeutic anti-CMV agents. Longer follow-up will be needed to assess the impact of letermovir prophylaxis on non-relapse and overall mortality. Disclosures Derigs: MSD: Honoraria. Müller-Tidow:MSD: Membership on an entity's Board of Directors or advisory committees. Luft:Neovii: Research Funding; JAZZ: Research Funding. Dreger:MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; AbbVie, AstraZeneca, Gilead, Janssen, Novartis, Riemser, Roche: Consultancy; Neovii, Riemser: Research Funding; AbbVie, Gilead, Novartis, Riemser, Roche: Speakers Bureau. Schmitt:MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; Therakos Mallinckrodt: Other: Financial Support.

Introduction: Systemic steroids with their strong immunosuppressive and anti-inflammatory effects are the current gold standard for initial treatment of the graft-versus-host disease (GvHD). But, the effectiveness of high-dose steroids comes along with an increased susceptibility to infections and other secondary malignancies. Extracorporeal photophoresis (ECP), an immunotherapeutic therapy, is currently being used as a clinically well-established second-line treatment for GvHD. Contrary to steroid treatment, there is no clinical data showing that ECP is associated with an increased risk of infection. However, the exact mechanism of action how ECP preserves the anti-viral and anti-leukemic effects on the cellular level has not been discovered yet. Materials and methods: Thirty-four patients with steroid-refractory/resistant aGvHD ≥ II and moderate to severe cGvHD were treated with ECP at the University Hospitals in Heidelberg, Greifswald in Germany and Chaim Sheba Medical Center in Israel. A comprehensive analysis of cell subsets was performed using multi-parametric flow cytometry. Additionally, the quantity and quality of CMV-specific T cells was determined by tetramer staining and interferon-γ enzyme-linked immunospot assay. The NK activity in terms of killing functionality and cytokine release was analyzed by intracellular cytokine staining and chromium-51 release assay, respectively. The proliferative capacity of effector cells was determined by carboxyfluorescein succinimidyl ester (CFSE) staining. Results: ECP therapy was effective with an overall response rate of 75% for patients with aGvHD (x/y) and 78% (x/y) for patients with cGvHD. Of note, all patients showed neither the increased susceptibility to infections nor the reactivation of CMV nor the tumor relapse. Overall, the frequency of well-established protective cell subsets in terms of cytotoxic CD8+ T cells, CD4+CD8+ T cells, γδ T cells, NK cells and NKT cells remained constant under the ECP therapy. Specifically, no significant influence of ECP therapy on the CD56dimCD57+NKG2C+ NK cells, a specialized anti-viral/tumor population, and the CMV+CD8+ T cells could be observed. The further phenotyping of CMV+CD8+ T cells showed that CD45RA+CCR7-CMV+CD8+ TE cells and CD45RA-CCR7-CMV+CD8+ TEM cells could keep stable under the ECP therapy. Besides these, priming, differentiation and maturation of NK cells through upregulation of CD57 by ECP therapy bridged the T-cell-deficient period after HSCT in order to control the viral infections and eliminate the residual malignant cells. Moreover, ECP could reduce the CD62L expression on TE population which not only facilitates the hematopoietic engraftment and contributes to the phenotypic and functional T cell reconstitution after transplantation without causing GvHD, but also enhances the functional immune reconstitution against tumor and viral antigens. Functionally, neither IFN-g released by virus specific T cells nor production of TNF-a and IFN-g by NK cells in response to K562 cells was hampered by ECP. Of note, the functions of NK cells in terms of the MFI of cytokines and the polyfunctionality of NK cells were stable under ECP treatment. Additionally, the proliferation of NK cells, CD4+ T cells and CD8+ T cells providing an expanded pool of effector cells against the pathogens was not hampered by ECP therapy as well. Conclusions: ECP therapy constitutes an effective strategy to treat GvHD. In addition, ECP appears to be a safe therapy compared to continued steroid use. Our current results suggest that ECP allows to maintain immunity against infections and tumors. Disclosures Schönland: Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Medac: Other: Travel Grant. Dreger:Neovii, Riemser: Research Funding; AbbVie, Gilead, Novartis, Riemser, Roche: Speakers Bureau; AbbVie, AstraZeneca, Gilead, Janssen, Novartis, Riemser, Roche: Consultancy; MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia. Schmitt:MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; Therakos Mallinckrodt: Other: Financial Support. Schmitt:Therakos Mallinckrodt: Other: Financial Support .

Although alloHCT is an accepted salvage treatment in defined settings of poor-risk NHL, its potential benefit in these indications remains controversial because virtually all published studies are uncontrolled and restricted to patients who were actually able to undergo transplantation. Here, we aimed at assessing the impact of alloHCT by measuring its outcome from the time of donor search indication rather than from the time of transplant, thereby taking into account those patients who fail to proceed to allografting for any reason. Study design and patients : In a single centre retrospective analysis, course and outcome of all patients with diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL) mantle cell lymphoma (MCL) and peripheral T-cell lymphoma (PTCL) who were considered as having an alloHCT indication according to accepted guidelines between 2004 and 2018 were recorded. Primary endpoint was overall survival (OS) from start of donor search. A key secondary endpoint was comparison of OS from the 3-month landmark by donor availability. Accepted donors were matched related donors (MRD), 10/10 matched unrelated donors (MUD), 9/10 compatible unrelated donors (MMUD), and mismatched related donors (MMRD), with haplo donors being used at our institution only since 2014. Results : Altogether a donor search was initiated in 187 patients (DLBCL 32%, FL 17%, MCL 23%, PTCL 28%). Median age was 54 (19-69) years with 74% being male. Within a median time from diagnosis to search initiation of 1.1 (0.1-19) years, a median of 4 (1-9) treatment lines had been administered, including an autoHCT in 50%. 69% of the patients had active disease at the time of search initiation. Only 2 patients underwent donor search in 1st remission (for Richter transformation and hepatosplenic T cell lymphoma, respectively). With a median follow-up of 6.2 (0.6-15.9) years, OS at 5 years after search initiation for DLBCL, FL, MCL, and PTCL was 25%, 44%, 52%, and 50%, respectively (Fig 1). 171 patients (91%) were alive at the 3-month landmark. For these, an MRD (20%), MUD (44%), MMUD (25%), or MMRD (7%) could be identified in 96% of the cases. AlloHCT was performed in 72% of all 187 patients, and in 79% of the patients alive at the 3-month landmark, with a significantly lower rate in DLBCL (69%) compared to the other entities. In patients who were actually transplanted, 5-year OS from landmark for DLBCL, FL, MCL and PTCL was 32%, 63%, 62%, and 62%, respectively, whereas only 5 of the 36 patients (14%) alive at the 3-month landmark not undergoing alloHCT for any reason survived long term. Due to the low rate of unsuccessful searches, donor vs no-donor landmark survival analyses were not possible. Conclusions: Despite donor search now being successful in virtually all cases, 20-30% of those patients intended for alloHCT for NHL will never proceed to transplant. However, long-term OS by ITT does not seem substantially worse than alloHCT outcome observed in registry studies restricted to patients actually transplanted, with DLBCL appearing inferior to the other 3 entities. Patients surviving the 3-month landmark but not undergoing alloHCT for any reason have a poor outlook. These results may serve as benchmark for novel therapeutic options entering the NHL treatment landscape. Disclosures Luft: Neovii: Research Funding; JAZZ: Research Funding. Schmitt:MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; Therakos Mallinckrodt: Other: Financial Support. Dreger:Neovii, Riemser: Research Funding; MSD: Membership on an entity's Board of Directors or advisory committees, Other: Sponsoring of Symposia; AbbVie, Gilead, Novartis, Riemser, Roche: Speakers Bureau; AbbVie, AstraZeneca, Gilead, Janssen, Novartis, Riemser, Roche: Consultancy.

Acute graft-versus-host disease (GVHD) is a major complication of allogeneic stem cell transplantation (SCT) and can be readily controlled by systemic high-dose steroids in many patients. However, patients whose GVHD is refractory to this therapy have a poor prognosis. Refractory patients have ongoing end-organ damage despite effective immunosuppression with second-line regimens, suggesting pathomechanisms independent from the initiating T-cell attack. To explore whether endothelial damage might contribute to GVHD refractoriness and to study the role of angiopoietin-2 (ANG2) in this process, we have compared kinetics of T-cell activation markers and markers of endothelial dysfunction in the serum of patients with sensitive (n = 23) and refractory GVHD (n = 25). Longitudinal measurements of soluble FAS ligand along with other immune markers demonstrate that refractory patients are not exposed to an overwhelming or unresponsive T-cell attack. However, in contrast to sensitive GVHD, refractory GVHD was associated with rising thrombomodulin levels and high ANG2/ vascular endothelial-derived growth factor ratios. Patients with refractory GVHD showed significantly increased ANG2 levels already before SCT. These results suggest that endothelial cell vulnerability and dysfunction, rather than refractory T-cell activity, drives treatment refractoriness of GVHD and opens new avenues for prediction and control of this devastating condition.

Background: Diminishing potential to replace damaged tissues is a hallmark for aging of somatic stem cells, but the mechanisms leading to aging remain elusive. Applying comprehensive proteomics studies on human hematopoietic stem and progenitor cells (HPCs) as well as 5 other cell populations that constitute the bone marrow niche, we have acquired a systems understanding of the mechanisms involved in aging of HPCs. Methods and materials: We present a proteome-wide atlas of age-associated alterations in HPCs along with 5 other cell populations including mesenchymal stromal cells (MSC) that comprise the bone marrow niche. For each, the abundance of a large fraction of the ~12,000 proteins identified was assessed in a cohort of 59 human subjects from different age groups. In selected samples, transcriptomics, metabolomics, and single cell RNA-Sequencing studies were simultaneously performed. Results: As the HPCs become older, one of the most prominent changes is the increase in abundance of proteins involved in the pathways for central carbon metabolism. This change is found only in HPCs and is reminiscent of the Warburg effect where glycolytic intermediates are rerouted towards pentose phosphate shunt and anabolism. Transcriptomic data confirm the increase in abundance of mRNA for the respective glycolytic enzymes in older HPCs. Metabolomics analyses provide further proofs demonstrating the trend towards anabolism upon aging. Altered abundance of early regulators of HPC differentiation reveals a reduced functionality and a bias towards myeloid differentiation at the expense of lymphoid development. Simultaneously, significant and complementary alterations in the bone marrow niche are observed. Whereas key factors responsible for homing, egress and adhesion of HPCs, e.g. SDF1/CXCL12, VCAM1, FN1, integrins α4, αL, β1 andβ2 decrease in abundance in MSCs, soluble factors responsible for myeloid differentiation, e.g.TGF-beta1, increase in abundance in the cellular niche with age. Transcriptomic analyses of single-sorted HPCs have demonstrated unequivocally that the mRNA levels of age-dependent increase in glycolytic enzymes are expressed at significantly higher levels in myeloid-biased versus than those in lymphoid-biased HPCs, whereas age-unaffected enzymes have similar mRNA levels in both subsets. The increase in abundance of glycolytic enzymes is hence linked with skewing of myeloid-biased HPCs in older human subjects. Conclusion: We have generated a comprehensive atlas of alterations in proteome landscapes of human HPCs and niche cells in bone marrow upon aging. In addition to findings that recapitulate the results derived from murine studies, the major novelties are (a) the alterations in central carbon metabolism in aging human HPCs, (b) the complementary decrease in levels of adhesive molecules and respective ligands in MSCs and HPCs. Single-cell studies have demonstrated that the age-related increase in abundance of the glycolytic enzymes is linked to the myeloid-biased HPCs. These data represent a valuable resource and serve as a basis for development of strategies targeting metabolic changes to enhance HPC regeneration. Disclosures No relevant conflicts of interest to declare.

Metabolic syndrome (MetS) is defined as a clustering of five factors including (1) fasting hyperglycaemia (2) hypertriglyceridaemia (3) low HDL cholesterol (4) hypertension (5) obesity (high waist circumference). According to the International Diabetes Federation harmonised definition, a large waist circumference plus any other two features meet criteria for diagnosis of MetS. It is associated with raised risk of cardiovascular disease (CVD) by 3-fold and is increasingly recognised in patients after HCT. Recent guidelines for long-term HCT survivors recommend screening for MetS. We performed a large cross-sectional service evaluation of HCT survivors in centres working in accordance with international screening guidelines. We have previously presented interim results regarding the prevalence of MetS and associated risk factors and now present the final results. This was an EBMT approved cross-sectional, non-interventional study of consecutive HCT patients (allo and auto) aged 18+ years and a minimum of 2 year post-transplant attending routine follow-up HCT and/or late effects clinics in 9 centres. Centres completed proformas incorporating routine recording of the MetS parameters (given above) as well as performance status (ECOG); evidence of cardiovascular events; family history of premature CVD; and relevant drug history. Univariate comparison of patients and HCT characteristics between the 2 groups (MetS vs no MetS) was performed using non-parametric Mann-Witney U test for continuous variables and Chi-square test or Fisher test for categorical variables. All tests were two-sided. Multivariate logistic regression analyses were performed to predict MetS and cardiovascular events. Variables with a p-value Table 1 gives the population demographic, age, primary disease and transplant details. The prevalence of MetS was 30.4% (allo 29%, auto 35.6% ns). There was a significant difference in prevalence by age at follow-up (p This large study in HCT survivors confirms high prevalence of metabolic syndrome following both allogeneic and autologous HCT of 30.4% overall rising to 39% in those aged over 50 years at follow-up. The data support MetS being an age-related late effect of HCT that is strongly associated with not only cardiovascular events but also the occurrence of second cancers. Further analysis examining the relationship between intensity of treatment and prevalence of MetS and CVE is needed. The data supports routine screening for MetS of both allo and auto HCT patients. Early intervention of reversible features of MetS with lifestyle and medical management may reduce the risk of cardiovascular events, but this needs be tested in a randomised controlled trial setting. Meanwhile, screening and management should be robustly integrated within routine HCT long-term follow-up care. Table 1. Table 1. Disclosures Cortelezzi: janssen: Consultancy; novartis: Consultancy; roche: Consultancy; abbvie: Consultancy. Mohty:Jazz Pharmaceuticals: Honoraria, Research Funding, Speakers Bureau; Servier: Consultancy; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; MaaT Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Speakers Bureau; Bristol Myers: Consultancy, Research Funding; Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Molmed: Consultancy; Janssen: Honoraria, Research Funding, Speakers Bureau. Kroeger:Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Riemser: Honoraria, Research Funding; JAZZ: Honoraria; Sanofi: Honoraria; Neovii: Honoraria, Research Funding. Snowden:Jazz & Sanofi: Other: Speaker fees at ASH; Jannssen/J&J: Other: Speaker fees.