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Key Points Systemic immune microenvironment signatures in CMML indicate an altered T- and natural killer cell balance. CMML bone marrow dendritic cell aggregates associate with disease progression and systemic regulatory T-cell phenotypic switch.

Background: Myelofibrosis (MF) is characterized by progressive bone marrow (BM) fibrosis resulting from aberrant megakaryopoiesis and expression of pro-inflammatory cytokines. These processes, heavily influenced by bromodomain and extraterminal domain (BET) protein-mediated gene regulation, lead to myeloproliferation and cytopenias. There is a high unmet need for a treatment that can potentially delay or reverse BM fibrosis in patients (pts) with MF. Pelabresib (CPI-0610) is a potent, first-in-class, selective, oral small-molecule BET inhibitor, which is able to modify the expression of genes involved in nuclear factor kappa B (NFκB) signaling in pts with MF. Pelabresib is currently being investigated as a monotherapy and in combination with the JAK inhibitor (JAKi) ruxolitinib (RUX), in the ongoing MANIFEST Phase 2 study (NCT02158858). Methods: In arm 1 of MANIFEST, pelabresib is administered as monotherapy to pts with MF who are intolerant/refractory to, or ineligible for RUX; in arm 2, as an 'add-on' to RUX in pts with MF who have suboptimal/lost response; and in arm 3 as combination therapy with RUX in JAKi treatment-naïve pts with MF. To evaluate the effects of pelabresib on BM biology, analyses were conducted using BM biopsy samples obtained pre-treatment and at 24 weeks post-treatment during the MANIFEST trial. Central pathology review of reticulin staining was conducted to evaluate BM fibrosis (BMF) grading and immunohistochemistry staining for changes in erythroids (ERY) and megakaryocytes (MK), respectively. Independent digital images of stained BM slides were also evaluated with a semi-quantitative cell-specific detection algorithm for reticulin density, percentage CD71+ ERY, mean number of CD61+ MK and mean distance between nuclei for CD61+ MK. Results: Exploratory analyses across the three treatment arms showed BM improvements after 24 weeks of treatment. Paired comparison by digital analysis of baseline and 24-week treatment BM biopsies from 29 pts showed reduction (range 67%-15.5%) in reticulin intersections per field in 45% (13/29) pts. Furthermore, digital analysis of CD71+ ERY and CD61+ MK from paired biopsies showed increased ERY progenitors in 50% (16/32) pts, decreased MK density in 57% (15/26) pts and decreased MK clustering in 46% (12/26) pts at 24 weeks. Decreased MK clustering correlated with decreased density of CD61+ MK in 75% pts (9/12). Correlative analysis between observed clinical responses and bone marrow improvements are ongoing and will be available for presentation at the conference. We previously reported (Talpaz M, et al. ASH 2020; Abstract 2163) that in pts with MF, pelabresib can reduce spleen volume, improve symptoms, improve bone marrow fibrosis, demonstrate increase in hemoglobin levels, and reduce transfusion burden. Updated 24-week data reflecting a higher number of evaluable pts and new long-term data at 48 weeks across the MANIFEST trial, will be presented. Conclusions: Treatment with pelabresib as monotherapy or in combination with RUX, in both RUX treatment-naïve and -experienced pts with MF, resulted in increased ERY progenitors, decreased MK density and reduction of BM fibrosis, as assessed by digital pathology. These data suggest possible disease-modifying potential for pelabresib by improving BM histology and function, leading to potential clinical benefits. Disclosures Verstovsek: Roche: Research Funding; Promedior: Research Funding; Blueprint Medicines Corp: Research Funding; Incyte Corporation: Consultancy, Research Funding; Protagonist Therapeutics: Research Funding; Genentech: Research Funding; CTI BioPharma: Research Funding; Celgene: Consultancy, Research Funding; Gilead: Research Funding; Ital Pharma: Research Funding; PharmaEssentia: Research Funding; NS Pharma: Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. Salama: Mayo Clinic: Current Employment, Other: Mayo Clinic had the contractual work for the central pathology review for this study and I was one of the reviewing pathologists; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Mascarenhas: AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Prelude: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Galecto: Consultancy; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding; Forbius: Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Talpaz: Celgene: Consultancy; Imago: Consultancy; Takeda: Other: Grant/research support ; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mesa: La Jolla Pharma: Consultancy; Samus: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; Pharma: Consultancy; CTI: Research Funding; Abbvie: Research Funding; CTI: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; AOP: Consultancy. Vannucchi: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rampal: Incyte: Consultancy, Research Funding; Pharmaessentia: Consultancy; Blueprint: Consultancy; Disc Medicine: Consultancy; Stemline: Consultancy, Research Funding; BMS/Celgene: Consultancy; Novartis: Consultancy; Sierra Oncology: Consultancy; CTI: Consultancy; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Memorial Sloan Kettering: Current Employment; Kartos: Consultancy. Oh: Abbvie: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Celgene Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Disc Medicine: Membership on an entity's Board of Directors or advisory committees; Geron: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Kartos Therapeutics: Membership on an entity's Board of Directors or advisory committees; PharamaEssentia: Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Membership on an entity's Board of Directors or advisory committees. Taverna: Constellation Pharmaceuticals: Current Employment. Cui: Constellation Pharmaceuticals: Current Employment. Zavidij: Constellation Pharmaceuticals: Current Employment. Chen: Constellation Pharmaceuticals: Current Employment. Colak: Constellation Pharmaceuticals: Current Employment. Efuni: Constellation Pharmaceuticals: Current Employment. Keller: Constellation Pharmaceuticals: Current Employment. Trojer: Constellation Pharmaceuticals: Current Employment. Harrison: Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte Corporation: Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Sierra Oncology: Honoraria; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Introduction: Chronic myelomonocytic leukemia (CMML) is a chronic myeloid malignancy associated with monocytosis, autoimmunity (~30%) & an inherent risk for leukemic transformation. Bone marrow (BM) dendritic cell (DC) populations occur in ~30% of patients, with a poorly defined biological & prognostic role. The malignant immune microenvironment is regulated by indoleamine 2,3-dioxygenase-1 (IDO-1) expressing DCs, which modulate regulatory T (Treg) cells & block their conversion into proinflammatory T helper (Th17)-like cells. IDO-1 is a known immune checkpoint & functions by catabolizing tryptophan, an amino acid essential for T cell function. We hypothesized that distinct IDO-1 expressing DC populations in CMML modulate Tregs & contribute towards immune tolerance & aggressive disease biology. Methods: Primary diagnostic CMML peripheral blood mononuclear cells (PBMC) & BM biopsy specimens were obtained after Mayo Clinic IRB approval. A DC population was defined on H&E stained biopsy sections as focal collections (>10) of cells with characteristic elongated nuclei & cytoplasmic extensions. Transcriptomic & protein expression studies assessing IDO-1 expression were done by previously described methods. In addition, IHC expression of PD-1, PD-L1 & CTLA-4 was also done. IDO-1 promoter methylation studies with DIP-seq were performed. The impact on immune tolerance was assessed using mass cytometry (CyTOF). Results: Cohort: Twenty eight patients with CMML were included in the study, median age 70 (range: 51-80) years; 71% males. Eleven (39%) patients had coexisting autoimmune conditions. Of these, 8 (73%) had detectable DC populations either at diagnosis, or during the course of their disease. At a median follow-up of 46 (95% CI 27, 84) months, there were 14 (50%) deaths & 9 (32%) leukemic transformations.IHC results: Nine (32%) patients were identified to have a DC population at CMML diagnosis. CD123 & TCL1 staining was performed in 5 (56%) patients, with 3 being positive for both, & 2 positive for CD123 only (additional IHC studies ongoing). IDO1 expression by IHC was documented in all 9 (100%) cases (Fig 1A & 1B), while rare populations of PD-1, PD-L1 & CTLA-4 lymphocytes were also seen in all cases. Due to the low DC burdens (median cellularity ≤ 5%) & uniform staining intensity, IHC-based grading was not done. Samples at serial time-points, post-HMA therapy & at the time of blast transformation, were available in 5 & 3 patients respectively. Among the patients who did not have DC populations at diagnosis, 5 (42%) developed them post-HMA therapy, while 3 (50%) developed them at the time of LT. The development of DC populations was associated with loss of response to HMA (50%) & disease progression (50%).Transcriptomic analysis: RNA expression data was available on 7 (25%) patients, of whom only 1 (14%) had DC populations at diagnosis. The IDO-1 RPKM value in the former was higher than the mean pooled value in the latter group (330 versus 74, p=0.05).Methylation studies: DIP-seq was performed on 12 (43%) cases from the primary IHC cohort. Qualitative analysis of IDO-1 promoter hypomethylation was conducted & confirmed in all 9 (100%) cases with 5-mC & 5-hmC marks compared to input as displayed in figure 1C.Immune profiling: CyTOF was performed on 4 CMML samples (3 with IDO-1 expressing DC populations at diagnosis) from the primary IHC cohort & compared to a normal PBMC control. Results confirmed an increase in DC populations (fig 1D& 1E), & reduced % of Th17-like T cells in CMML samples compared to control (1.1 versus 5.07, p=0.05, fig 1F).Clinical correlates & survival analysis: With the exception that CMML patients with DC populations had a higher frequency of NRAS (P=0.007) mutations, the two groups were comparable for cytogenetic & molecular abnormalities. The median OS for the cohort was 45 (95% CI 29, 84) months. CMML patients with IDO-1 expressing DC populations at diagnosis had a shorter median OS, in comparison to those without (median OS 30 vs 45, p=0.03, Kaplan-Meier analysis in fig 1G). Conclusions: In conclusion, we demonstrate that DC populations are seen in ~30% of patients with CMML with a uniform expression of IDO-1 & limited expression of PD-1, PD-L1 & CTLA-4. CMML patients with BM DC populations have a higher frequency of NRAS mutations & DC IDO-1 expression is associated with tumor induced immune tolerance. Additional IHC, genomic & preclinical studies with IDO-1 inhibitors are ongoing. Figure 1. Figure 1. Disclosures Al-Kali: Novartis: Research Funding.

Hodgkin lymphoma (HL) originates from the clonal expansion of malignant Hodgkin and Reed-Sternberg (HRS) cells. These B-cell–derived elements constitute less than 10% of the tumoral mass. The remaining tissue is comprised of an inflammatory infiltrate that includes myeloid cells. Myeloid cells activate B cells by producing BAFF and APRIL, which engage TACI, BCMA, and BAFF-R receptors on the B cells. Here, we studied the role of BAFF and APRIL in HL. Inflammatory and HRS cells from HL tumors expressed BAFF and APRIL. Unlike their putative germinal center B-cell precursors, HRS cells lacked BAFF-R, but expressed TACI and BCMA, a phenotype similar to that of plasmacytoid B cells. BAFF and APRIL enhanced HRS cell survival and proliferation by delivering nonredundant signals via TACI and BCMA receptors through both autocrine and paracrine pathways. These signals caused NF-κB activation; Bcl-2, Bcl-xL, and c-Myc up-regulation; and Bax down-regulation, and were amplified by APRIL-binding proteoglycans on HRS cells. Interruption of BAFF and APRIL signaling by TACI-Ig decoy receptor, which binds to and neutralizes BAFF and APRIL, or by small-interfering RNAs targeting BAFF, APRIL, TACI, and BCMA inhibited HRS cell accumulation in vitro and might attenuate HL expansion in vivo.

To the editor: In a recent paper in Blood , Haroche et al reported dramatic efficacy of vemurafenib in 3 cases of multisystem and refractory Erdheim-Chester disease (ECD) and Langerhans cell histiocytosis harboring the BRAF V600E mutation.[1][1] The findings of an ∼50% prevalence of BRAF

Cohesin complex members have recently been identified as putative tumor suppressors in hematologic and epithelial malignancies. The cohesin complex guides chromosome segregation, however cohesin-mutant leukemias do not show genomic instability suggesting an alternate role in malignant transformation. We hypothesized reduced cohesin function alters chromatin structure and disrupts cis-regulatory architecture of hematopoietic stem/progenitor cells. We therefore investigated the impact of both complete loss and haploinsufficiency of Smc3, an obligate member of the cohesin complex, in normal hematopoiesis and in myeloid transformation by developing a conditional Smc3 knockout allele. Somatic loss of Smc3 in hematopoietic cells induced lethal bone marrow aplasia (median survival 11 days; p To further explore the mechanism by which Smc3 loss cooperates with Flt3ITD to induce leukemia, we investigated chromatin cis-regulatory architecture with transposase hypersensitivity assays (ATAC-seq). We hypothesized that increased accessibility at cis-regulatory elements and the alterations in gene expression seen in cells with combined Smc3 haploinsufficiency and Flt3ITD may be in a large part driven by potentiated Stat signaling at chromatin. We analyzed 146 transcription factor recognition motifs within the THS differentially observed in Smc3Δ/+Flt3ITD and wild-type cells. Chromatin accessibility gained in Smc3Δ/+Flt3ITD cells are enriched in Stat family transcription factor binding sites, including Stat5. We also observed enrichment of the Stat5 gene expression signature in the Smc3Δ/+Flt3ITD cells compared to Smc3Δ/+, Flt3ITD and wild-type cells, suggesting the divergent mutations cooperate to potentiate oncogenic Stat5 signaling in HSPCs. Our results demonstrate a key dose-dependent role for the cohesin complex in hematopoiesis, and show that reduced cohesin functions to alter enhancer-mediated transcription and contribute to aberrant self-renewal and myeloid transformation. Figure 1. Figure 1. Disclosures Levine: Loxo Oncology: Membership on an entity's Board of Directors or advisory committees; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees; Foundation Medicine: Consultancy.

Context Akt plays an essential role in diverse cellular processes such as cell proliferation, cell growth and apoptosis. Dysregulation of Akt signaling has been shown to correlate with an inferior survival in patients with a number of solid tumors and some hematologic malignances. The prognostic significance of Akt expression and the gene expression profile of Akt activation in diffuse large B-cell lymphoma (DLBCL) have not been thoroughly assessed. Objective In this study, we investigated Akt activation and analyzed its prognostic importance in a large cohort of patients with de novoDLBCL treated with R-CHOP immunochemotherapy. We also characterized the gene expression profile of DLBCL with activated Akt. Patients The study group consisted of 493 DLBCL patients treated with R-CHOP. These cases were organized as a part of the International DLBCL R-CHOP Consortium Program Study, and diagnosed according to the WHO criteria. Patients with primary mediastinal large B-cell lymphoma, primary cutaneous DLBCL, primary central nervous system DLBCL, and DLBCLs transformed from a low-grade B-cell lymphoma or associated with HIV infection were excluded. Methods Immunohistochemical studies (IHC) were performed in formalin-fixed paraffin-embedded sections of tissue microarrays to evaluate the expression of phosphorylated (activated) Akt and other relevant markers. Genetic alterations were examined by FISH for MYC, BCL-2, and BCL-6 translocations and sequencing for TP53 mutation. Gene expression profiling (GEP) was performed to characterize the gene expression profile in Akt-activated DLBCL. The cell-of-origin (COO) subtypes were determined by GEP (gold standard) and IHC. Results Phosphorylated (activated) Akt (pAkt) expression was detected in 98 of 493 (20%) DLBCL tumors including 49 of 253 (19%) GCB DLBCL and 49 of 240 (20%) ABC DLBCL. In the GCB subtype, MYC, BCL-2 and MYC/BCL-2 translocations were more frequently found in pAkt+ DLBCL compared with pAkt- DLBCL (P=0.04, 0.007 and 0.03, respectively). In contrast, translocations of these genes were rare and detected equally in pAkt+ and pAkt- subgroups within the ABC subtype (P=0.7, 0.9 and 0.9, respectively). In the GCB group, TP53 mutation frequency was similar between pAkt+ and pAkt- DLBCL (P=0.45). In contrast, TP53 mutations were significantly less frequent in ABC group (5% versus 22%; P= 0.01). Akt activation predicted a poorer survival, but the negative prognostic impact of Akt activation was significant in the ABC (5-year survival rate: 44% in pAkt+ versus 65% in pAkt-; P=0.01; 5-year PFS: 40% in pAkt+ versus 59% in pAkt-; P=0.01), but not GCB subtype (5-year survival rate: 67% in pAkt+ versus 74% in pAkt-, P=0.31; 5-year PFS rate: 61% in pAkt+ versus 69% in pAkt-, P=0.27). The negative impact of Akt activation appeared to be independent of Myc/Bcl-2 expression and TP53 mutation. In multivariate analysis, pAkt expression was an independent predictor of poorer OS (HR=2.72, 95% CI, 1.50-4.98, P=0.001) and PFS (HR=2.16, 95% CI, 1.22-3.82, P=0.008) in patients with ABC wild type-TP53. In addition, AKT1 mRNA expression conferred significantly poor survival in DLBCL. Gene expression profiling revealed a distinct high-risk signature characterized by increased expression of multiple pro-survival genes (6 of 16 up-regulated genes; 40%) and decreased expression of genes encoding tumor suppressors (5 of 20 down-regulated genes; 25%) in pAkt+ ABC DLBCL. Conclusions Akt is activated in DLBCL, is equally distributed in COO subtypes, and has prognostic significance in patients with ABC DLBCL. Given the promising anti-lymphoma activity of Akt inhibitors in clinical trials, these findings may have clinical implications for DLBCL patients. Akt activation may be useful for prognostic stratification and could serve as a biomarker to guide patient selection and predict response to targeted anti-Akt therapy. Disclosures No relevant conflicts of interest to declare.

Introduction Expression of signal transducer and activator of transcription 3 (STAT3) in de novo diffuse large B-cell lymphoma (DLBCL) has not been studied broadly and the prognostic value of STAT3 expression in DLBCL is controversial. Methods The study group included 876 de novo DLBCL patients. All patients were treated with rituximab, cyclophosphamide, hydroxydoxorubicin, vincristine and prednisone (R-CHOP). Cases excluded from the study group included large cell transformation from low-grade B-cell lymphoma, primary cutaneous large B-cell lymphoma, primary mediastinal large B-cell lymphoma, primary DLBCL of the central nervous system and cases associated with Epstein-Barr virus or human immunodeficiency virus. Immunohistochemical (IHC) studies for several biomarkers were performed using fixed, paraffin embedded sections of tissue microarrays. Fluorescence in situ hybridization (FISH) for BCL2, BCL6, MYC, and TP53 were performed andTP53 was also sequenced Gene expression profiling (GEP) was performed on 500 cases and the cell of origin (COO) classification was determined by GEP (gold standard) and immunohistochemistry. Results STAT3 was positive in 240 (32.9%) patients, including 133 men and 107 women. The median age of STAT3+ DLBCL patients was 65 years (range, 21-93) and was similar to STAT3- DLBCL patients (63, range 12-95). B symptoms (44.4% vs. 35.2%, P=0.021) and advanced stage (60.5% vs. 52.1%, P=0.035) were more commonly present in STAT3+ DLBCL compared with STAT3- DLBCL patients. Other clinical characteristics were similar between the groups. STAT3+ DBLCLs were more often activated B-cell (ABC) type than STAT3- DLBCLs (61.8% vs. 41.1%, P Conclusion STAT3 is expressed in approximately 1/3 of de novo DLBCLs. STAT3 expression is associated with B symptoms, advanced stage of disease, ABC type, and expression of MYC. Expression of p50 and p65 are more frequently expressed in STAT3+ DLBCL, illustrating activated NF-κB through canonical pathway. C-Rel is less commonly expressed in STAT3+ DLBCL, suggesting p65 is the principal partner for p50. Genetic aberrations are rare. Although STAT3 expression is associated with several adverse prognostic parameters, it does not confer inferior OS and PFS in DLBCL overall, suggestive of the presence of yet unidentified putative tumor suppressive functions in STAT3+ DLBCL patients. Disclosures: Winter: Millenium: Research Funding; Novartis : Research Funding; Pfizer (Wyeth): Research Funding; Seattle Genetics: Research Funding; Spectrum: Research Funding; Janssen (Pharmacyclics): Research Funding; Spectrum (Allos): Consultancy; Sanofi Aventis: Consultancy; Tgen: Consultancy; AMBIT Biosciences (Spouse): Research Funding; Celgene (Spouse): DSMB, DSMB Other, Research Funding; Ariad Pharmaceuticals (Spouse): Research Funding; Novartis (Spouse): Consultancy, Research Funding; Amgen (Spouse): Consultancy, Research Funding; Astellas (Spouse): Research Funding; Caremark/CVS: Consultancy; Pfizer (Spouse): Consultancy; Sanofi Aventis (Spouse): DSMB, DSMB Other; Bristol Myers Squibb (Spouse): DSMB, DSMB Other; UptoDate, Inc.(Spouse): Patents & Royalties.

Context and objective Approximately 5-10% of diffuse large B-cell lymphoma (DLBCL) patients carry MYC gene translocations (MYC-translocation+) with a poor prognosis after standard chemotherapy. MYC-translocation+ DLBCL patients carrying BCL2 translocations (MYC+/BCL2+ double-hit lymphoma) have a worse survival. The efficacy of adjuvant radiotherapy in this setting is unknown. The purpose of this study is to evaluate the efficacy of radiotherapy as a part of the therapeutic regimen for patients with MYC-translocation+ DLBCL. Patients and methods From the International DLBCL R-CHOP consortium program, we selected 581 patients with de novo DLBCL treated with standard R-CHOP immunochemotherapy (diagnosed and treated from 2000 to 2010). We excluded patients with transformed DLBCL, primary mediastinal, cutaneous, testicular or central nervous system large B-cell lymphomas, patients with HIV infection, and patients not treated with R-CHOP. The median follow-up was 54.9 months. Fluorescence in situ hybridization assessing MYC was performed for all the patients (n=581) and results were correlated with available clinical data to identify clinicopathologic features associated with MYC translocation, and to evaluate the prognostic significance of MYC translocations regarding overall survival (OS, from the time of diagnosis to death from any cause) and progression-free survival (PFS, from the time of diagnosis to relapse or death from any cause). In the MYC-translocation+ DLBCL group, 38 patients received chemotherapy alone and 21 patients received chemotherapy with adjuvant radiation therapy. The clinicopathologic features and survival of MYC-translocation+ DLBCL patients treated with (n=21) and without radiotherapy (n=38) after immunochemotherapy were compared to in order to evaluate the radiotherapy efficacy and other confounding factors. Results MYC translocations were detected in 59 DLBCL patients (10.2%). Patients with MYC-translocation+ DLBCL more often had bulky tumors, involvement of multiple extranodal sites, and poorer OS (hazard ratio [HR]: 2.0, 95% confidence interval [CI]: 1.20 - 3.35, P= .0083) and PFS (HR: 1.96, 95% CI: 1.22 - 3.13, P= .0005) independent of the International Prognostic Index score. Poor survival was primarily attributable to patients with MYC+/BCL2+ double-hit DLBCL who were predominantly of germinal center B-cell subtype. Among MYC-translocation+ DLBCL patients, a better survival was achieved in patients who received radiotherapy (for OS, HR: .32, 95% CI: .15 - .71, P= .0049; for PFS, HR: .35, 95% CI: .17 - .73, P= .0043). Conversely, radiotherapy abolished the adverse impact of MYC translocations. In addition, radiotherapy was associated with better survival in the subset of patients with MYC+/BCL2+ double-hit lymphoma (P = .017 for OS, and P = .05 for PFS). However, owing to the common use of radiotherapy as consolidation therapy, the favorable prognoses in the group of patients who received radiotherapy could also be attributed to limited-stage disease and more frequent complete remission (CR) after first-line treatment and therefore these factors confound interpretation of the data. To address these issues, we evaluated radiotherapy efficacy in separate patient groups: patients who achieved CR, non-CR (PR/SD/PD) patients, and patient with stage I/II, or stage III/IV disease. The efficacy of radiotherapy appeared more apparent in patients with advanced disease who did not achieve CR after first-line chemotherapy. Multivariate analysis after adjustment for stage and IPI score validated that radiotherapy significantly improved OS (HR: .28, 95% CI: .10 - .81, P= .018) and PFS (HR: .32, 95% CI: .13 - .80, P= .015) of MYC-translocation+ DLBCL patients. Conclusions The presence of MYC translocations in DLBCL is an important biomarker that facilitates prognostic prediction and treatment stratification independent of the IPI score. For chemoresistant MYC-translocation+ DLBCL patients, radiotherapy seems to be an effective adjuvant regimen likely due to the higher frequency of extranodal involvement and bulky disease in MYC-translocation+ DLBCL patients. Our results provide a rationale for larger scale studies to assess the potential role of radiotherapy in the management of MYC-translocation+ DLBCL patients, particularly patients with MYC+/BCL2+double-hit DLBCL. Disclosures: Winter: Millenium: Research Funding; Novartis : Research Funding; Pfizer (Wyeth): Research Funding; Seattle Genetics: Research Funding; Spectrum: Research Funding; Janssen (Pharmacyclics): Research Funding; Spectrum (Allos): Consultancy; Sanofi Aventis: Consultancy; Tgen: Consultancy; AMBIT Biosciences (Spouse): Research Funding; Celgene (Spouse): DSMB, DSMB Other, Research Funding; Ariad Pharmaceuticals (Spouse): Research Funding; Novartis (Spouse): Consultancy, Research Funding; Amgen (Spouse): Consultancy, Research Funding; Astellas (Spouse): Research Funding; Caremark/CVS: Consultancy; Pfizer (Spouse): Consultancy; Sanofi Aventis (Spouse): DSMB, DSMB Other; Bristol Myers Squibb (Spouse): DSMB, DSMB Other; UptoDate, Inc.(Spouse): Patents & Royalties.

Abstract 2706 Objective: Adult T-cell leukemia/lymphoma (ATLL) is a mature T-cell malignancy associated with human T-cell lymphotropic virus -1 (HTLV-1) infection. Four clinical subtypes are recognized including acute/lymphomatous (aggressive) or chronic/smouldering (indolent). For the aggressive subtypes the median overall survival is 6 months despite aggressive combination chemotherapy. Novel therapeutic targets against CD25, CD52, and NF μB have shown preliminary activity in ATLL. Recently, the chemokine receptor 4 (CCR4) antibody (KW-0761) was approved in Japan based on a phase II overall response rate of 50% and median overall survival of 13.7 months in 28 patients with relapsed/refractory ATLL. CD30 (Ki-1) is a marker of immune activation expressed on lymphocytes, and is an emerging target in lymphoma. The novel antibody-drug conjugate brentuximab vedotin targets CD30 and has shown efficacy in Hodgkin lymphoma and anaplastic large cell lymphoma (ALCL). While CD30 positive ATLL is infrequent in Japanese ATLL patients, ranging from 12.1% to 19.4%, the prevalence of CD30 positive ATLL outside of Japan has not been extensively studied. Patients and Methods: To investigate the prevalence of CD30 expression and its importance in ATLL outside of Japan we conducted a retrospective review of all patients who underwent treatment or consultation for ATLL at our institution between 1998 and 2012. Individual chart review was performed to report the clinical presentation, pathological features, and outcomes. Pathology review of CD30 expression status was conducted if specimens were available. The CD30 (Ber-H2) antibody from Ventana was used on automated platforms per manufacturer's instructions. Specimens were determined to be positive if the CD30 expression was >20% by an expert hematopathologist (AC). Results: We identified 50 patients with ATLL. Patient characteristics were: median age 54 (range 30–82); male:female 19:31; Caribbean-39, American-6, Western African-2, Peruvian-2, and Greek-1. Subtype of disease at diagnosis was: Acute/Lymphomatous—41 and Chronic/Smouldering—9. Thirty-six of 50 (72%) patients' samples had been tested at least once for CD30. Eighteen patients (50%) were reported positive. Of all cases reviewed (N=50), eight had pathology available for confirmatory review. Of those, five patients remained positive, 1 patient was reclassified as positive after initially being reported as negative, and two remained negative. The median overall survival of all patients was 13 months. In the subset who had CD30 status assessed the median overall survival for CD30 negative and positive ATLL was 18 and 45 months respectively (p=0.116). Conclusions: CD30 expression on normal lymphocytes is rare. Our retrospective data suggests that ATLL patients presenting outside of Japan may demonstrate CD30 positivity at a higher prevalence compared to Japanese reports. In pre-clinical studies of CD30 positive ATLL, SGN-35 has been shown in vitro and in vivo to demonstrate similar cytotoxicity compared to ALCL (Maeda et al. Cancer Sci 2010). Novel strategies are clearly needed to improve the outcome of ATLL despite recent advances. Therefore, CD30 testing may be considered in ATLL as a novel target for future research strategies. Disclosures: Matasar: GSK: Research Funding; Genentech: Consultancy. Straus:Seattle Genetics: Consultancy. Zelenetz:GSK: Consultancy, Research Funding; Genentech/Roche: Consultancy, Research Funding; Gilead: Consultancy; Sanofi Aventis: Consultancy; Cephalon: Consultancy; Celgene: Consultancy; Seattle Genetics: Consultancy; Amgen: Research Funding. Horwitz:Seattle Genetics: Consultancy, Research Funding; Allos: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy; Genzyme: Consultancy; Kyowa Hakko Kirin Pharma: Consultancy; Johnson & Johnson: Consultancy; Infinity Pharmaceuticals, Inc.: Research Funding.

Abstract 544 Background: In DLBCL, multiple extranodal sites of involvement and MYC/BCL2 translocations (double hit lymphoma) are associated with a poor clinical outcome. The association between the pattern of extranodal involvement and MYC and BCL2 protein expression, as well as the prognostic significance of expression, are unknown. Methods: We analyzed the clinical data of 487 DLBCL patients treated with R-CHOP. Immunohistochemical (IHC) studies were performed on paraffin-embedded tissue samples for MYC and BCL2. A double-hit score (DHS) of 0, 1, or 2 was assigned to all patients based on protein expression of MYC and BCL2. Those with both MYC and BCL2 expression were DHS 2, with MYC or BCL2 was DHS 1, and neither was DHS 0. Cell-of-origin classification was achieved by combining gene expression profiling (GEP) and IHC data with GEP as the gold standard. Patient characteristics were compared using Fisher's exact test. Survival analyses were performed using Kaplan-Meier curves and compared using log-rank test. The Cox proportional regression model was used for multivariate analysis. Results: Approximately half of the patients (n = 251; 51.5%) had at least 1 extranodal site of involvement. In this group, the clinical features were: median age of 63 years (range, 12–88), male (58.6%), stage III/IV (63.2%), elevated serum LDH (66.8%), and International Prognostic Index (IPI) of 3–5 (48.5%). IHC features were: non-germinal center B-cell like (non-GCB) (53%), MYC+ (64.9%), BCL2+ (49.8%), MYC-/BCL2- (DHS 0; 20.3%), MYC+/BCL2- or MYC-/BCL2+ (DHS 1; 44.6%) and MYC+/BCL2+ (DHS 2; 35.1%). The common extranodal sites of involvement were genitourinary tract (18.3%), gastrointestinal tract (15.1%), sinonasal (14.3%), bones (13.9 %), lung (11.6 %), skin/soft tissues (9.9%), liver (9.1%), and bone marrow (8.4%). MYC+ was associated with bone marrow (odds ratio [OR]: 5.67; P = 0.009) and skin (OR: 3.11; P = 0.045) involvement, BCL2+ with sinonasal (OR: 2.26; P = 0.032) involvement, and MYC+/BCL2+ with skin/soft tissue (OR: 2.38; P = 0.049) and lung (OR: 2.37; P = 0.04) involvement. Non-GCB subtype was associated with genitourinary tract (OR: 1.47; P = 0.005) and bone marrow involvement (OR: 1.5; P = 0.038). The DHS 2 subgroup was significantly associated with lower complete response rate (62.5% vs 76.1%; P = 0.023), shorter progression-free-survival (PFS) (median 23.1 months vs 80.7 months; P < 0.001), and shorter overall survival (OS) (median 25.0 months vs 94.5 months; P < 0.001) compared with the DHS 0–1 subgroups. Using multivariate analysis, DHS 2 remained significantly associated with a worse outcome. Conclusions: In DLBCL with extranodal disease, MYC and BCL2 protein expressions and cell-of-origin are associated with distinct patterns of organ involvement. Patients with DLBCL expressing both MYC and BCL2 (score DHS 2; double hit biology) have a poor outcome independent of IPI and cell-of-origin. Disclosures: No relevant conflicts of interest to declare.

Abstract 949 Introduction: Diffuse large B cell lymphoma (DLBCL) has a highly variable outcome, and individual risk assessment is largely based on clinical features. Gene expression profiling (GEP) stratifies patients into those with germinal center B-cell (GCB) and activated B-cell subtype (ABC) subtype with different prognoses. These groups have been shown to predict prognosis in patients treated with CHOP or R-CHOP. Conversely, the role of other recognized prognostic markers, such as BCL2 gene abnormalities or Bcl2 expression has been questioned in the new therapeutic era. Materials and Methods: In 438 patients treated with R-CHOP for de novo DLBCL, we analyzed the tumors by immunohistochemistry for Bcl2 protein expression and by interphase fluorescence in situ hybridization (FISH) for BCL2 translocation and other abnormalities. All cases were successfully studied by GEP. The cutoff for Bcl2 protein expression, 60%, used as prognostic factor was determined using receiver operating characteristic curves. Progression-free survival (PFS) and overall survival (OS) were assessed. Results: The t(14;18)(q32;q21) was detected in 82 cases (18.7%) and BCL2 gains occurred in 63 cases (14.3%). Both t(14;18) and BCL2 gains strongly correlated with higher levels of Bcl2 protein expression (p60%) tumors had significantly inferior PFS in the GCB subgroup (p=0.03), but not in the ABC subgroup (p=0.54). Multivariate analysis revealed that the presence of the t(14;18), but not Bcl2 protein expression, was independent of the International Prognostic Index in predicting outcome of our patients. Conclusions: Patients with the GCB subtype and t(14;18) exhibit a significantly worse prognosis than patients without t(14;18) when treated with R-CHOP. The assessment of t(14;18) by FISH approach not only functions as a valuable prognosticator for individual risk estimation in GCB-DLBCL patients in addition to the established parameters, but also provides valuable result for therapeutic intervention. Disclosures: No relevant conflicts of interest to declare.

Abstract 967 Mutations of the TP53 tumor suppressor gene are associated with a poor clinical outcome in DLBCL patients treated with CHOP. The impact of TP53 mutations on clinical outcome of DLBCL patients treated with Rituxan-CHOP has not been comprehensively analyzed. The purpose of this study was to analyze the frequency and type of TP53 mutations in Rituxan-CHOP treated DLBCL patients from twenty-two medical centers, and to correlate these with clinical outcome. TP53 mutations were identified in 138/604 (22.7%) Rituxan-CHOP treated DLBCL cases and included missense (n=133), nonsense (n=16), splice site (n=9) and frameshift (n=1) mutations. The presence of any TP53 mutation correlated with poor overall survival (OS) with a median OS of 50 months in the TP53 mutation group versus 69 months in the wild-type group (wt-TP53, P=0.0042). Seventy-three of 138 cases (53%) had mutations in the DNA binding domains of the TP53 gene, which were found to be the most important predictor of poor OS (P=0.0044). In contrast, mutations in the non-DNA binding domains did not correlate with poor OS (P=0.157). Overexpression of p53 protein significantly correlated with only TP53 missense mutations (P=0.002), but not with other types of TP53 mutations, while TP53 deletion did not correlate with mutation or OS. In comparison to our previous series of patients treated only with CHOP, Rituxan-CHOP regimen improved OS in both wt-TP53 and TP53 mutated groups. The 5-year survival rate was 42% in patients with any TP53 mutation (median survival=50 months) and 41% in patients with the DNA-binding domain mutations (median survival=49 months) compared to 52% for those with wt-TP53 (median survival=69 months). The complete remission rate was 51% in patients with any TP53 mutation and 44% in patients with the DNA-binding domain mutations, compared to 77% for those with wt-TP53. However, the clinical outcome and treatment response to the Rituxan-CHOP varied in patients with mutations in different regions of the DNA-binding domains. Patients with mutations in the DNA minor binding groove motif (Loop L3, 17% of all mutations) had significantly decreased median OS (17 months) when compared to patients with Loop L2 (16% of all mutations) or loop-sheet-helix motifs (Loop L1-S10-H2, 20% of all mutations) with median OS of 49 and 50 months, respectively. In contrast to our previous CHOP series study, median survival was significantly improved for Rituxan-CHOP treated DLBCL patients with mutations in the loop-sheet-helix motifs (43 months). Multivariate analysis confirmed that TP53 mutations and activated B-cell-like (ABC)/germinal center B-cell-like (GCB) subtype classification were independent predictors of OS with a hazard ratio of 0.69 (GCB vs ABC, 95% CI 0.49-0.98) and 1.60 (TP53 vs wt-TP53, 95% CI 1.10-2.31), respectively. Similar to our previous CHOP study, the TP53 mutation profile, regardless of location, was found to stratify GCB-DLBCL, but not ABC-DLBCL, into molecularly distinct subsets with different clinical outcomes in Rituxan-CHOP treated DLBCL patients. This study demonstrates the importance of TP53 mutational profile for predicting clinical outcome. Elucidation of the roles of specific TP53 domain mutations, as documented in our study, will help in refining prognostic models for DLBCL patients treated with either the CHOP or Rituxan-CHOP regimen. These findings also provide the rationale and strategies for p53 targeted therapeutic intervention in DLBCL patients. Disclosures: Kahl: Milllennium: Consultancy, Research Funding; Cephalon: Consultancy, Research Funding.

Class switching from immunoglobulin M (IgM) to IgG, IgA or IgE is central to immunity against viruses and requires activation of B cells by CD4+ T cells through CD40 ligand (CD40L). Human immunodeficiency virus (HIV) evades protective T cell-dependent IgG and IgA responses against viral proteins and vaccines through mechanisms that remain unknown. Recent findings from our lab suggested the involvement of negative factor (Nef), an HIV accessory protein that suppresses CD40 signaling in B cells. The present work addressed the mechanism by which Nef invades B cells. Fluorescence microscopy-based studies showed that accumulation of Nef in infected lymphoid follicles was associated with severe loss of activation-induced cytidine deaminase (AID), a Nef-targeted DNA-editing enzyme essential for class switching. Loss of follicular AID correlated with in vivo inactivation of CD40 signaling and formation of long-distance membrane tethers connecting Nef-positive B cells with HIV-infected macrophages. By combining confocal microscopy, videomicroscopy and electron microscopy with standard molecular biology techniques, we demonstrated that macrophages harboring HIV or expressing a chimeric Nef-green-fluorescent protein were capable of transferring Nef-containing cargos to B cells via long-distance, actin-propelled and energy-dependent membrane channels, including tunneling nanotubules. Transfer of Nef to B cells involved a clathrin-dependent pathway that required the guanine nucleotide exchange factor Vav as well as downstream Rho, Rac and Ccd42 small GTPases. This pathway led to Nef-mediated inhibition of CD40-induced AID expression and IgG and IgA class switching. In summary, our findings indicate that HIV evades T cell-dependent IgG and IgA responses by shuttling virus-encoded Ig class switch-suppressing factors from infected macrophages to non-infected B cells via long-range membrane tethers, including tunneling nanotubules.

Hairy cell leukemia (HCL) is a rare chronic lymphoproliferative disorder characterized by massive infiltration of the spleen by malignant B cells displaying a distinctive “hairy” morphology. These hairy cells (HCs) often contain hypermutated Ig genes, suggesting an ontogenetic relationship with post-germinal center memory B cells. However, unlike memory B cells, HCs usually express CD11c and CD103, two molecules typically associated with mucosal innate immune cells. The goal of this study was to elucidate the ontogeny and growth mechanisms of HCs. We found that HCs interacted with splenic endothelial cells expressing B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL), two innate B cell-stimulating factors involved in T cell-independent antibody responses, including Ig class switching. In agreement with prior studies indicating that BAFF and APRIL play an important role in B cell tumors, HCs expressed transmembrane activator and calcium modulator and cyclophylin ligand interactor (TACI), B cell maturation antigen (BCMA), and BAFF receptor (BAFF-R), three receptors that bind BAFF and APRIL. In addition, HCs expressed microbial carbohydrate and endocytic receptors usually expressed by innate immune cells, including DEC-205 (CD205), mannose receptor (CD206), langerin (CD207) and dendritic cell-specific ICAM-3-grabbing non-integrin (CD209). This phenotype was different from that of naïve, germinal center, memory and plasmacytoid B cells, but similar to that of a subset of splenic marginal zone and mucosal B cells. Like these innate B cells, HCs contained activation-induced cytidine deaminase, a DNA-editing enzyme required for class switching, and showed signs of ongoing IgM-to-IgD class switching, a mucosal Ig diversifying process typically triggered by BAFF and APRIL. Our findings suggest that HCL may emerge as a result of chronic stimulation of an innate B cell precursor through a T-cell independent pathway involving microbial carbohydrates, BAFF and APRIL.

Introduction. Hairy cell leukemia (HCL) is a rare chronic B cell lymphoproliferative disorder characterized by massive infiltration of the spleen by cells displaying a unique “hairy” morphology and surface phenotype. The ontogeny of hairy cells (HCs) and the mechanism underlying their accumulation in the spleen remain elusive. Growing evidence indicates that B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL) play important roles in malignant B cells. BAFF and APRIL are usually produced by myeloid cells and engage three receptors on B cells known as transmembrane activator and calcium modulator and cyclophylin ligand interactor (TACI), B cell maturation antigen (BCMA), and BAFF receptor (BAFF-R). APRIL binding to TACI and BCMA is reinforced by cell-anchored and matrix-associated heparan-sulphate proteoglycans (HSPGs). In this study we verified the role of BAFF and APRIL in HCL. Methods. Splenic tissue sections and B cells from 5 healthy donors and 5 HCL patients were analyzed for expression of BAFF, APRIL, TACI, BCMA, BAFF-R and other molecules through immunohistochemistry, immunofluorescence, flow cytometry, immunoblotting and quantitative real-time RT-PCR. HCs were also cultured with umbilical vein or splenic endothelial cells in the presence or absence of BAFF and APRIL inhibitors, including soluble TACI-Ig decoy receptor, small interfering RNAs (siRNAs) and HSPG-modifying agents, such as heparinitase. HC proliferation, survival and signaling as induced by recombinant BAFF or APRIL were evaluated through standard assays. Results. We found that splenic sinusoids surrounding HCs were comprised of endothelial cells expressing APRIL and, to a lesser extent, BAFF. Endothelial cells up-regulated BAFF and APRIL upon exposure to HC-derived cytokines, including TNF-α. Unlike naïve, germinal center, memory and plasmacytoid B cells but similar to splenic marginal zone B cells, HCs expressed high levels of TACI, BCMA, BAFF-R and HSPGs together with CD1c, CD11c, CD27, CD83, CD123, endocytic receptors, and carbohydrate receptors. Preliminary data indicated that endothelial cells stimulated HCs through a mechanism involving BAFF, APRIL and HSPGs as pretreatment of endothelial cells with BAFF and APRIL small interfering RNAs or heparinitase attenuated the growth and survival of HCs in co-cultures. TACI-Ig, which binds to and neutralizes BAFF and APRIL, had a similar inhibitory effect. Conversely, BAFF, APRIL as well as TACI, BCMA or BAFF-R cross-linking stimulated HC growth. This stimulation was associated with NF-κB activation as well as up-regulation of various pro-survival and growth-inducing intracellular proteins. Conclusions. The present findings suggest that HCs may derive from a splenic marginal zone B cell precursor. In addition, our studies indicate that splenic sinusoids form a BAFF-APRIL-HSPG-rich niche that promotes HC expansion via TACI, BCMA and BAFF-R. Finally, our data suggest that blocking BAFF and APRIL through TACI-Ig, siRNAs and HSPG-modifying agents could have therapeutic value in HCL.

Imatinib, a tyrosine kinase inhibitor, is effective in treating erythrocytosis and splenomegaly in many PV patients (pts), but is less effective controlling thrombocytosis or splenomegaly in others. Imatinib in PV pts may inhibit c-kit signaling, essential for erythroid progenitor proliferation and/or PDGF-R signaling. The JAK2 V617F mutation is present in most PV pts. We found imatinib therapy in PV pts resulted in a modest molecular response based on %V617F that correlated with hematologic improvement/clinical response; however, those who achieved complete hematological remission had initially lower %V617F. Here we correlate bone marrow (BM) morphology and immunophenotype with clinical/molecular response to imatinib in 10 pts fulfilling criteria for PV (8 men, 2 women; 28–72 yr) treated with imatinib (400–800 mg/day) for 5–31 mo. Cytogenetics in 1 pt showed +9; 4 were normal. CR was defined as phlebotomy-free within18 mo. of treatment (Tx), HCT level 400×109/L and 30/20x). Imatinib Tx resulted in decreased erythroid cells; less granulopoiesis; and no change/increased MKs with clustering and shedding of CD61+ platelets clumps into stroma. 2 cases progressed to fibrosis.The proliferation was variable (15–30%) with no change on Tx. C-mpl expression in MKs decreased with disease progression. The % cells expressing CD34 and/or CD117 was low and did not change. We found BM morphologic and immunophenotypic changes correlate with clinical/molecular response to imatinib in PV pts. Thus, BM evaluation may be helpful in assessing severity/disease progression and identifying pts who may benefit from imatinib Tx. The findings also suggest heterogeneity of hematopoietic stem cell proliferation. Targeting JAK2/other pathways involved in MK proliferation/migration may be beneficial in PV pts with large numbers of MKs who likely progress to fibrosis.

Introduction. Class switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods. Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in class switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results. We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing class switch DNA recombination (CSR). Epithelial cells released innate class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial class switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions. The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.

Background: Germinal center (GC) and non-germinal center (non-GC) gene expression profiles correlate with survival in immunocompetent DLBCL patients. Phenotypic expression patterns of CD10, BCL6, MUM1 and CD138 are surrogates for genetic studies with comparable survival data; CD10+, BCL6+/−, MUM1- defines GC while CD10-, BCL6-, MUM1+/− identifies the non-GC phenotype with poorer prognosis. Expression of FOXP1, a transcription factor differentially expressed in resting and activated B cells, and PRDM1/BLIMP1, a regulator of terminal B cell differentiation, are also adverse prognostic markers for DLBCL in immunocompetent patients. AIDS-associated DLBCLs from uniformly treated HIV+ patients in AMC010 (CHOP vs. CHOP-rituxan) and AMC034 (EPOCH vs. EPOCH-rituxan) were examined to determine if the GC vs. non-GC phenotype, FOXP1 expression and/or BLIMP1 expression are prognostic in this patient population. Design: Slides of 32 and 30 AIDS-associated DLBCLs from AMC010 (closed) and AMC034 (in analysis) patients, respectively, were available for FOXP1, BLIMP1, CD10, BCL6, MUM1, BCL2, Ki-67 immunohistochemistry and in situ hybridization for EBV (EBER). Antigen expression by >20% tumor cells (>10% for BLIMP1) was considered positive. GC phenotype was defined as CD10+, BCL6+/−, MUM1- while the non-GC cases were CD10-, BCL6-, MUM1+/−. Overall survival (OS) based on GC vs. non-GC phenotype was examined. FOXP1 expression was correlated with survival; BCL2, Ki-67 expression; and EBV status; BLIMP1 expression was correlated with survival in a subgroup of patients from AMC 034. Results: Of the 62 cases, 59% were MUM1, 60% BCL6, 53% CD10, 59% BCL2, 49% FOXP1, 67% BLIMP1 and 30% EBER positive. 19 (58%) cases were classified as GC and 14 as non-GC. No mean OS difference between GC and non-GC groups (p=0.74) or FOXP1+ and FOXP1- cases (p=0.8; t-test) in the AMC 010 patients; BLIMP1 expression did not correlate with survival in the subgroup of AMC 034 patients (p=0.4). GC vs. non-GC phenotype did not correlate with FOXP1 expression (p=0.1) or BLIMP1 expression (p=0.4). In addition, FOXP1 expression did not correlate with EBV positivity, BCL2, MUM1, BCL6 or CD10 expression or proliferation rate based on Ki67 (chi-square). Conclusions: AIDS-associated DLBCLs can be classified as GC and non-GC cases, but this classification does not appear to correlate with prognosis/OS in uniformly treated HIV-positive patients. Furthermore, in contrast with immunocompetent DLBCLs, FOXP1 expression also does not correlate with OS in this patient population; similarly BLIMP1 expression also does not correlate with survival in the HIV+ patient population. In addition, GC vs non-GC phenotype did not correlate with FOXP1 or BLIMP1 expression, while FOXP1 expression did not correlate with prognostic markers BCL2/Ki67 or EBV status. Thus, prognostic markers useful in immunocompetent patients with DLBCL may not be relevant for HIV positive patients, suggesting that patient immune status rather than tumor biology may be more important in predicting patient outcome.

Background. Class switch DNA recombination (CSR) from IgM to IgG and IgA is central to immunity against pathogens and requires the activation of B cells by CD4+ T cells through CD40 ligand (CD40L) and cytokines, including IL-4 and IL-10. Viruses evade protective IgG and IgA responses through a number of strategies, including production of soluble proteins that suppress T cell-dependent (TD) class switching in bystander B cells. HIV-1 is thought to impair antigen-specific IgG and IgA production by inducing progressive depletion of CD4+ T cells. Although important, this mechanism is not sufficient to explain the intrinsically poor response of B cells from viremic patients to CD4+ T cell help. This prompted us to explore the B cell-modulating activity of negative factor (Nef), an early HIV-1 protein implicated in immunosuppression. Nef is released in the extracellular environment by infected cells and might perturb the function of bystander B cells by targeting them through its N-terminal myristoylated domain. Methods. Tonsillar tissue sections from healthy donors and lymph nodal tissue sections from 10 HIV-1-infected patients were analyzed for IgD, p24, and Nef expression by immunohistochemistry. Nef expression was also analyzed in IgD+ B cells purified from healthy donors and exposed to a recombinant myristoylated or non-myristoylated Nef protein. These IgD+ B cells as well as an IgD+ B cell line expressing a wild-type Nef transgene or a mutant Nef transgene lacking the myristoylated domain were utilized in CSR assays after further exposure to CD40L, IL-4 and IL-10. CSR and signaling were studied as described1,2,3. Results. We found that HIV-1-infected lymphoid follicles express large amounts of Nef. This viral protein penetrates in bystander B cells both in vivo and in vitro and interferes with the initiation of CSR by CD40L and cytokines without down-regulating CD40 and cytokine receptor expression on B cells. Rather, Nef up-regulates inhibitor of NF-κ B (Iκ B) and suppressor of cytokine signaling (SOCS) proteins, including SOCS1 and SOCS3, in B cells. These powerful inhibitory proteins attenuate the transcriptional activation of germline Ig gene promoters by blocking CD40 and cytokine receptor signaling through NF-κ B and signal transducer and activator of transcription (STAT), respectively. In addition, Nef hampers the up-regulation of key components of the CSR machinery, such as activation-induced cytidine deaminase (AID), and blocks the induction of IgG, IgA and IgE secretion by CD40L and cytokines. Under similar conditions, Nef spares B cell survival, B cell proliferation as well as B cell signaling through mitogen-activated protein kinase p38 and B cell-specific activation protein (BSAP or Pax5). Conclusions. Our findings suggest that HIV-1 inhibits IgG and IgA production not only by impairing CD4+ T cells, but also by turning on powerful CSR inhibitory pathways in bystander B cells through Nef. We propose that Nef-blocking agents might improve protective antibody responses to pathogens and vaccines in HIV-1-infected patients.

Introduction. B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL), a BAFF-related molecule, play a key role in the survival and proliferation of mature B cells. In addition, BAFF and APRIL cooperate with IL-4 to induce class switch DNA recombination (CSR) from IgM (or IgG) to IgG, IgA or IgE. This process requires activation-induced-cytidine deaminase (AID), a DNA-editing enzyme involved also in Ig somatic hypermutation and lymphomagenesis. BAFF and APRIL are usually produced by myeloid cells, including dendritic cells, macrophages and granulocytes, and engage three receptors preferentially expressed on B cells, including transmembrane activator and calcium modulator and cyclophylin ligand interactor (TACI), B cell maturation antigen (BCMA), and BAFF receptor (BAFF-R). Our previous studies show that BAFF and APRIL are EBV-inducible molecules implicated in B cell non-Hodgkin’s lymphoma (NHL). The scope of the present studies was to elucidate the expression and function of BAFF, APRIL, TACI, BCMA and BAFF-R in Hodgkin lymphoma (HL). Methods. Tissue sections from 5 primary EBV+ HL cases and 5 primary EBV− HL cases were analyzed for BAFF, APRIL, TACI, BCMA, and BAFF-R expression through immunohistochemistry. RS cells from 6 primary cases were microdissected and analyzed for the expression of AID and CSR byproducts by RT-PCR. The expression of BAFF, APRIL, TACI, BCMA, BAFF-R, AID, and CSR byproducts was also analyzed in 5 HL cell lines cultured in the presence or absence of recombinant BAFF, APRIL and cytokines as previously described1,2,3. Results. We found that the reactive infiltrate of primary HL tumors comprises non-malignant elements, such as macrophages, granulocytes and plasma cells, expressing BAFF and APRIL. Also a variable proportion of malignant CD30+ Reed-Sternberg (RS) cells from both EBV+ and EBV− HL cases express BAFF and APRIL. Unlike NHL B cells, which usually express BAFF-R, primary RS cells and RS cell lines lack BAFF-R, but express TACI and BCMA. In the presence of BAFF or APRIL, RS cell lines are rescued from spontaneous or induced apoptosis. This effect is associated with activation of NF-κB through a classical pathway. Increased RS cell survival is also associated with up-regulation of the pro-survival BCL-2 and BCL-XL proteins, and down-regulation of the pro-apoptotic BAX protein. Finally, in the presence of BAFF or APRIL and IL-4, RS cell lines up-regulate AID expression and increase their spontaneous CSR activity. Of note, AID expression extends to primary RS cells and is associated with ongoing CSR. Conclusions. Our studies indicate that BAFF and APRIL stimulate malignant RS cells through both autocrine and paracrine pathways. Engagement of TACI and BCMA receptors by BAFF and APRIL may enhance the expansion of RS cells by attenuating apoptosis through a mechanism involving NF-κB and BCL family proteins. By up-regulating AID, signals emanating from TACI and BCMA receptors might also introduce genomic instability. Finally, considering that TACI, BCMA and AID are B cell-specific molecules and that CSR is a process confined to B cells, our findings consolidate the notion that RS cells derive from a B cell precursor.