Novak, Anne J.

Abstract Background: Non-Hodgkin lymphomas (NHL) are increasing in incidence and are now the fifth most common tumor diagnosed each year in the United States. Most NHLs are of B-cell origin but the tumor tissue is variably infiltrated with T-cells. Our group has shown in diffuse B-cell large cell lymphoma, that a high number of intratumoral CD4+ T-cells predicts a better overall survival. It has been shown that recently-characterized CD4+CD25+ regulatory T-cells (Treg cells) played an important role in the mediation of anti-tumor immunity. However, there is no data on the role of intratumoral Treg cells in suppression of autologous infiltrating CD4+ T-cells in B-cell NHL. Goal: To investigate the effect of intratumoral Treg cells on the proliferation of tumor-infiltrating CD4+CD25- T-cells, to determine the underlying mechanism of the T-cell suppression, and evaluate the role that malignant B-cells may play in the recruitment of Treg cells to the site of B-cell NHL. Results: We identified a subset of CD4+CD25+ T-cells over-represented in biopsy specimens of B-cell NHL (these cells comprise 17% of cells in lymphoma biopsies, compared 7% of peripheral blood mononuclear cells, 12% of cells in inflammatory tonsil and 6% of cells in tumor free lymph nodes; p-value =0.001). These CD4+CD25+ T-cells are memory-like T-cells (CD45RO+ and CD45RA−) and express high levels of CTLA-4 and Foxp3 when compared to autologous tumor-infiltrating CD4+CD25- T-cells. Importantly, these CD4+CD25+ T-cells displayed the ability to suppress the proliferation and cytokine (IFN-g and IL-4) production of tumor-infiltrating CD4+CD25- T-cells in response to PHA stimulation. Treatment with anti-B7-H1 antibody or PD-1 fusion protein enhanced the proliferation of infiltrating CD4+CD25- T-cells when co-cultured with intratumoral CD4+CD25+ T-cells. Our results suggest that interaction between B7-H1 and PD-1 accounts for about 30% of intratumoral Treg cell-mediated inhibition of autologous infiltrating CD4+CD25- T-cells in tumor sites of B-cell NHL. Lastly, we found that CCL22 secreted by lymphoma B-cells is involved in the chemotaxis and migration of intratumoral CD4+CD25+ T-cells which express chemokine receptor CCR4, but not CCR8. Conclusion: Our results suggest that tumor microenvironmental CD4+CD25+ regulatory T-cells are important regulators of tumor immunity and that these cells are recruited to the area of lymphoma involvement by the malignant B-cells.

Abstract BACKGROUND Monocytes and macrophages (mo/mΦ) are a key part of the composition of peripheral blood (PB) and tissues and increased numbers of mo/mΦ have been associated with patient outcome in non-Hodgkin lymphoma (NHL). Because CD14 is abundantly expressed on the surface of human mo/mΦ, it is often used to identify or isolate human mo/mΦ, and immunosuppressive CD14+HLA-DRlow monocytes have been shown to be increased in the peripheral blood of NHL patients. However, we have previously shown that CD14 expression on mo/mΦ is substantially lower than CD68 expression suggesting that many CD68+ mo/mΦ are CD14 negative, especially in spleen and lymph node tissues. To characterize both CD14+ and CD14- mo/mΦ in PB and tissues, we isolated all mo/mΦ from B-cell NHL specimens and normal controls and assessed their phenotype and function. METHODS Human mo/mΦ were isolated by negative selection from PB and tissue biopsy specimens (B-cell NHL and normal tissues) using the immunomagnetic isolation (monocyte enrichment kit). Morphological and immunophenotypic characteristics of isolated mo/mΦ were determined by Giemsa stain and flow cytometry. Phagocytosis and migration assays were used to determine the function of isolated mo/mΦ. T cells were co-cultured with mo/mΦ and T cell proliferation was evaluated by CFSE staining and detected by flow cytometry. RESULTS Using a monocyte enrichment kit to isolate all mo/mΦ, the purity of isolated mo/mϕ was 85~99%, which was defined by the percentage of lineage-negative cells (i.e. cells without expression of CD3,CD19, CD20, and CD56). We found that these isolated mo/mΦ constituted 2 populations: a more frequent population of larger cells and a less common population of smaller cells. In contrast to PB, CD14 positive mo/mΦ constituted less than 40% of the tissue mo/mΦ from the isolated population. Furthermore, we found that the cell size from CD14+ mo/mΦ were larger than CD14- mo/mΦ. Using CD14 and SIRP-α, we could identify 3 populations of mo/mΦ: CD14+SIRP-αhigh, CD14-SIRP-αdim and CD14-SIRP-α- cells. CD14+SIRP-αhigh cells and CD14-SIRP-αdim cells typically constituted the population of larger cells, while CD14-SIRP-α- cells constituted the population of smaller cells. CD14-SIRP-α- cells lacked the typical phenotypic markers and had decreased phagocytic and migratory ability compared to CD14+SIRP-αhigh and CD14-SIRP-αdim cells. Furthermore, we found that these 3 populations of mo/mΦ had a differential effect on activated T-cells and that the CD14-SIRP-α- cells appeared increased number in biopsy specimens from NHL when compared to normal tissues. CONCLUSIONS We have identified a unique population of small CD68+ mo/mΦ that lack expression of CD14, SIRP-α, and other FcγR markers. This subset of mo/mΦ is more prevalent in NHL tissues and has limited phagocytic and migratory functions. This CD14-SIRP-α- mo/mΦ subpopulation may play an inhibitory role in anti-cancer and inflammatory responses. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Numerous studies have shown that lymphoma B-cells are resistant to CTL-mediated death, however the underlying mechanism for this resistance is not clear. In previous work, we have identified a subset of CD4+CD25+ T-cells overrepresented in the tumor sites of B-cell NHL that display a phenotype compatible with regulatory T cells (Treg cells). These cells express high levels of Foxp3 and CTLA-4, and are capable of suppressing the proliferation and cytokine production of autologous infiltrating CD4+CD25- T cells in B-cell NHL. Goal: To explore whether Treg cells exert a suppressive effect on the induction and function of autologous tumor-infiltrating CD8+ T-cells in B-cell NHL. Results: Using fresh specimens obtained from patients with B-cell lymphoma, we found that intratumoral Treg cells had a significantly suppressive effect on autologous tumor-infiltrating CD8+ T-cells in B-cell NHL. When activated CD8+ T-cells were cocultured with infiltrating CD4+CD25- T-cells, they displayed less proliferation than CD8+ T-cells cultured alone. However, we found that with a 1:4 ratio of stimulating cells (Treg cells) to responding cells (CD8+ T-cells), intratumoral Treg cells completely inhibited the proliferation of autologous tumor-infiltrating CD8+ T-cells activated with PHA. Furthermore, we have observed that 20% of infiltrating CD8+ T-cells in fresh isolated samples from B-cell NHL coexpress perforin and granzyme B. When intratumoral Treg cells were cocultured with CD8+ T-cells, the Treg cells inhibited the activation-induced production of perforin and granzyme B of autologous tumor-infiltrating CD8+ T-cells in a dose-dependent fashion. We also found that cytokine treatment (IL-2 and IL-12) or PHA activation induced the capability of tumor-infiltrating CD8+ T-cells to kill lymphoma B-cells, which was accompanied by upregulation of expression of CD107a on the surface of cytotoxic CD8+ T-cells. Intratumoral Treg cells significantly inhibit cytotoxicity of activated infiltrating CD8+ T-cells to lymphoma B-cells. Finally, we found that there was an inverse correlation of cell frequencies between intratumoral Treg cells and tumor-infiltrating CD8+ T cells in patients with B-cell NHL, suggesting that Treg cells may inhibit the migration of cytotoxic T-cells to the sites of B-cell lymphoma. Conclusion: Intratumoral Treg cells dramatically suppress the proliferation and activation-induced production of granules in infiltrating CD8+ T-cells in B-cell NHL. These Treg cells also inhibit the ability of activated tumor-infiltrating CD8+ T-cells to kill lymphoma B-cells in vitro, and may prevent the migration of CD8+ cells to the sites of lymphoma. Taken together, these data indicate an important role for intratumoral Treg cells in CTL-mediated anti-tumor immunity in B-cell NHL.

Abstract Waldenströms Macroglobulinemia (WM) is a unique form of lymphoplasmacytic lymphoma, in which the tumor compartment is comprised of B-lymphocytes, plasmacytoid lymphocytes and plasma cells. The majority of WM cases are immunophenotypically characterized by expression of surface antigens that are present on both B-cells (CD19/20) and plasma cells (CD38/138). However, in advanced stage disease, which has been treated with various chemoimmunotherapeutics the molecular profile of WM cells can drastically shift resulting in a majority of the WM tumor compartment exhibiting loss of CD20 and concurrent upregulation of atypical surface antigens (Barakat et al, Am J Clin Pathol 2011; Morice et al Mod Pathol 2009). These external immunophenotypic changes are associated with underlying epigenetic and genomic alterations, whose integrated study may provide further insight into the biology of advanced stage WM. Moreover, such an analysis holds clinical potential by uncovering of therapeutic vulnerabilities, which can direct the selection of appropriate therapeutics for patients with CD20- WM. With this in mind, we conducted comprehensive molecular testing coupled with functional studies to understand if underlying genomic/epigenetic changes correlated with drug sensitivity using appropriate preclinical models of CD20+ WM (BCWM.1 cell line) and CD20- WM (RPCI-WM1 cell line). Importantly, the index patient from whom the CD20- cells were developed had received a total of 6 lines of treatment, two of which contained rituximab and was documented as being refractory to rituximab. Immunophenotyping of CD20- cells showed differential downregulation of 19 and upregulation of 7 CD antigens relative to CD20+ WM cells (cutoff at 1.5 fold; >20% gated expression). Upregulated antigens were associated with a phenotype reminiscent of a memory B-cell with plasmacytoid features. Next, we conducted RNA-Seq analysis (Illumina HiSeq), which revealed downregulation of 6,673 and upregulation of 4,594 genes (>1.5 fold cutoff) in CD20- WM cells compared with CD20+ cells. Gene pathway enrichment analysis (NextBio, Illumina Inc.) of mRNA differentially expressed in CD20- cells showed significant enrichment of upregulated genes corresponding to Protein Transport (p<1.8E-98) and Response to Unfolded Protein Gene Ontology groups (p<5.9E-20). Interestingly, pathway analysis of downregulated genes in CD20- WM cells showed enrichment within the B-cell receptor-signaling (BCR) pathway (Broad MSigDB) (p<6.1E-14) relative to CD20+ WM cells. BCR signaling has been linked to dysregulated expression of several micro-RNAs (miRs). Consistent with pathway analysis results, we observed decreased levels of numerous miRs (Exiqon qPCR) in CD20- vs. CD20+ WM cells, which target and regulate components involved in BCR activation. To examine further epigenetic changes that may account for decreased BCR signaling, we examined the global methylation profile (Infinium HumanMethylation 450K array) of CD20- and CD20+ WM cells and noted hypermethylation of the promoter sites (200 base pairs upstream) for a number of transcription factors involved in the BCR pathway. We therefore examined sensitivity of CD20- WM cells to the BTK inhibitor ibrutinib, which abrogates BCR signaling. As anticipated, CD20- WM cells retained >90% viability and demonstrated significantly less apoptosis in presence of ibrutinib (4uM) compared to CD20+ cells, suggesting decreased reliance on canonical BCR signaling for survival. In parallel and guided by pathway analysis results, we exposed both CD20- and CD20+ WM cells to a novel 19S proteasome inhibitor (VLX1570), which caused profound proteotoxicity and ER stress at concentrations ranging between 250 – 500nM. We noted CD20- cells were significantly more sensitive (p<0.01) to 19S proteasome inhibition than CD20+ WM cells indicating the formers critical dependence on tightly regulated protein homeostasis. In summary we describe for the first time, a comprehensive molecular and immunophenotypic investigation of CD20- WM cells compared to CD20+ WM cells, using validated preclinical models of the two disease phenotypes. Overall our data suggests significant architectural differences between CD20+ and CD20- WM, which can potentially impact the behavior of the cells and their sensitivity towards novel therapeutics being developed for treatment of advanced stage WM. Disclosures Martin: Janssen: Honoraria.

Abstract Waldenstrom’s macroglobulinemia (WM) is a serious and frequently fatal disorder characterized by the production of a monoclonal IgM protein, a lymphoplasmacytic infiltrate in the bone marrow, and associated symptoms including anemia, lymphadenopathy and hyperviscosity. Many of the mechanisms leading to this disease are not yet known. It is clear, however, that there is dysregulation of the balance between cell proliferation and programmed cell death. BLyS (B-lymphocyte stimulator) is a TNF family member expressed by monocytes, neutrophils, macrophages, and dendritic cells. BLyS has been shown to be critical for maintenance of normal B cell development and homeostasis, and has been found to stimulate lymphocyte growth. BLyS is overexpressed in a variety of B-cell malignancies and has been shown to inhibit apoptosis in malignant B-cells. Studies of the effects of BLyS on B cell physiology have shown that it also regulates immunoglobulin secretion. In previous work, we have shown that malignant B cells from patients with WM are able to bind soluble BLyS and variably express the BLyS receptors, BAFF-R, TACI and BCMA. We also found expression of BLyS in bone marrow specimens by immunohistochemistry and elevated serum BLyS levels in patients with WM. The goal of this study was to determine the functional role of BLyS-receptor ligand system in Waldenstrom’s macroglobulinemia and its relevance to the increased immunoglobulin production seen in this disease. Using cells from WM patients, we first examined the ability of BLyS to increase the secretion of IgM by malignant B cells. BLyS, alone or in combination with cytokines that induce plasmacytic differentiation and immunoglobulin production (IL-2, IL-6, IL-10 and IL-12), was found to increase IgM secretion by malignant B cells. Mean baseline IgM levels significantly increased in cells treated with BLyS (p=0.03), cytokines (p=0.0002) and a combination of BLyS and cytokines (p<0.0001). We then determined the effect of BLyS on the survival of malignant B cells using Annexin-V/PI staining. Compared to cells cultured in media alone, BLyS was found to increase viability of malignant B cells from WM patients. Cell viability was normalized relative to the media-alone control and the median relative viability increased significantly compared to controls (median increase 41.2%; range 8 – 46%). Next, we examined the ability of BLyS to modulate cell proliferation using thymidine incorporation. Using WM patient samples, BLyS was found to significantly enhance the proliferation of malignant B cells (p=0.0002). Furthermore, addition of anti-Ig antibody further enhanced the ability of BLyS to promote the proliferation of malignant B cells (p<0.0001). In summary, we have demonstrated that BLyS enhances IgM secretion by malignant B cells from patients with Waldenstrom’s macroglobulinemia. We have also demonstrated the ability of BLyS to enhance the survival and proliferation of malignant B cells. Strategies to inhibit BLyS may potentially have therapeutic efficacy in Waldenstrom’s macroglobulinemia.

Abstract Background. Diffuse large B-cell lymphoma (DLBCL) is curable for the majority of patients treated with anthracycline based immunochemotherapy (IC). While most patients achieve response to initial therapy, a subset of patients are refractory to initial IC or become refractory to subsequent salvage therapies. Prognosis in this setting is very poor. Here we determine the incidence of refractory disease from a large cohort of DLBCL prospectively followed from diagnosis in the IC era and assess outcomes in these patients. Methods. Patients were prospectively enrolled in the University of Iowa/Mayo Clinic Lymphoma SPORE Molecular Epidemiology Resource (MER) within 9 months of diagnosis. Patients were followed for relapse, retreatment, and death; all events were validated by medical record. This analysis includes patients with DLBCL or primary mediastinal B-cell lymphoma (PMBCL) who received initial treatment of anthracycline based immunochemotherapy; patients with primary CNS lymphoma or post-transplant lymphoproliferative disorders were excluded. Response to therapy was retrospectively classified per 2007 Revised Response Criteria for Malignant Lymphoma from available clinical and radiology records. Refractory disease was defined as having a best response to any systemic therapy of stable disease (SD), progressive disease (PD), or relapse within 12 months of autologous stem cell transplantation (SCT). We also examined patients with transient response to IC as defined by achieving an interim response (CR or PR) but having progressive disease at or prior to the end of the planned number of cycles of IC. Results. 1039 patients with DLBCL or PMBCL lymphoma were enrolled in the MER from 2002-2012 and treated with R-CHOP or comparable IC. Median age at diagnosis was 62 years (range 18-91) and 577 (56%) were male. At a median FU of 60 months (range 1-148), 136 patients developed refractory disease. The median age at diagnosis of patients with refractory disease was 62 years (range 19-87). The cumulative incidence of refractory DLBCL was 11.3% at 2 years (95%: CI: 9.5-13.4) and 13.1% at 5 years (95% CI: 11.2-15.4). The median overall survival after becoming refractory was 4.7 months (95% CI: 4.1-5.5) with a 1 year survival rate of 21% (95% CI: 15%-30%). The median number of therapies before becoming refractory was 2 with 35 patients becoming refractory following their first therapy (i.e. IC), 83 patients becoming refractory after their 2nd therapy, and 23 patients becoming refractory after their 3rd or later therapy; 27 patients had received stem cell transplant prior to becoming refractory. Outcomes were poor regardless of when patients became refractory (figure). Patients received a median (range) of 2 (0-8) treatments after becoming refractory with 40% (N=54) attempting subsequent platinum based salvage therapy and 14% (N=9) proceeding to ASCT, of which only 6 remain alive in long-term remission. 41 patients (30%) were treated on clinical trials after becoming refractory. Response rate for the first therapy after becoming refractory was 21%, while 29% of patients had a response to any subsequent therapy. Once patients became refractory, there was no difference in survival based on response at end of initial IC (p=0.33), cell of origin at diagnosis (p=0.64), IPI at diagnosis (p=0.33), or age when refractory (p=0.66). Outcomes in patients with transient response to IC (n=58) were poor, with the majority (N=37, 63%) becoming refractory to subsequent therapy. Median OS after first relapse was 6.7 months in patients with transient response to IC, which was equivalent to patients refractory to IC (p=0.99). The majority of patients with transient response to IC (69%) were next treated with platinum based salvage therapy which had a response rate of 40%. Ultimately 15 of the 58 patients (26%) proceeded to transplant, of which only 5 (9%) achieved long-term remission. Conclusions. Approximately 13% of patients with DLBCL become refractory to treatment in their disease course. Outcomes once patients become refractory are extremely poor regardless of when patients become refractory. Standard prognostic factors are no longer predictive of outcome and stem cell transplant had limited benefit in this group of patients. Patients with transient response to initial immunochemotherapy should be included when classifying patients as refractory. New therapy strategies are needed in the refractory setting. Figure 1. Figure 1. Disclosures Maurer: Kite Pharma: Research Funding. Thompson:Kite Pharma: Research Funding. Farooq:Kite Pharma: Research Funding. Cerhan:Kite Pharma: Research Funding. Ansell:Bristol-Myers Squibb: Research Funding; Celldex: Research Funding. Link:Genentech: Consultancy, Research Funding; Kite Pharma: Research Funding.

Abstract Diffuse large B-cell lymphoma (DLBCL) is a genetically heterogeneous disease characterized by multiple low-frequency alterations including somatic mutations, copy number alterations (CNAs) and chromosomal rearrangements. We sought to identify previously unrecognized low-frequency genetic events, integrate recurrent alterations into comprehensive signatures and associate these signatures with clinical parameters. For these reasons, our multi-institutional international group assembled a cohort of 304 primary DLBCLs from newly diagnosed patients, 87% of whom were uniformly treated with state-of-the-art therapy (rituximab-containing CHOP regimen) and had long term followup. Tumors were subjected to whole exome sequencing with an extended bait set that included custom probes designed to capture recurrent chromosomal rearrangements. In this cohort, 47% of samples had available transcriptional profiling and assignment to associated disease subtypes. Analytical pipelines developed at the Broad Institute were used to detect mutations (MuTect), CNAs (Recapseq+Allelic Capseq) and chromosomal rearrangements (dRanger+Breakpointer) and assess clonality (Absolute). To analyze formalin-fixed paraffin-embedded tumors without paired normals we developed a method which utilized 8334 unrelated normal samples to stringently filter recurrent germline events and artifacts. Significant mutational drivers were identified using the MutSig2CV algorithm and recurrent CNAs were assessed with GISTIC2.0. In addition, we utilized a recently developed algorithm, CLUMPS2, to prioritize somatic mutations which cluster in 3-dimensional protein structure. With this approach, we identified > 90 recurrently mutated genes, 34 focal amplifications and 41 focal deletions, 20 arm-level events and > 200 chromosomal rearrangements in the DLBCL series. Of note, 33% of the mutational drivers were also perturbed by chromosomal rearrangements or CNAs, underscoring the importance of a comprehensive genetic analysis. In the large DLBCL series, we identified several previously unrecognized but potentially targetable alterations including mutations in NOTCH2 (8%) and TET2 (5%). The majority of identified chromosomal rearrangements involved translocations of potent regulatory regions to intact gene coding sequences. The most frequently rearrangements involved Ig regulatory elements which were translocated to BCL2, MYC, BCL6 and several additional genes with known roles in germinal center B-cell biology. After identifying recurrent somatic mutations, CNAs and chromosomal rearrangements, we performed hierarchical clustering and identified subsets of DLBCLs with comprehensive signatures comprised of specific alterations. A large subset of tumors shared recurrent alterations previously associated with follicular lymphoma including mutations of chromatin modifiers such as CREBBP, MLL2, and EZH2 in association with alterations of TNFRSF14 and GNA13 and translocations of BCL2. This cluster was enriched in GCB-type DLBCLs and contained a subset with select genetic alterations associated with an unfavorable outcome. An additional cohort of tumors was characterized by alterations perturbing B-cell differentiation including recurrent BCL6 translocations or alterations of PRDM1. A subset of these DLBCLs had alterations of NOTCH2 and additional pathway components or mutations of MYD88 in association with TNFAIP3, CD70 and EBF1, a master regulator of B-cell differentiation. An additional group of DLBCLs exhibited frequent MYD88 mutations in association with alterations of CD79B, PIM1, TBL1XR1 and ETV6 and BCL2 copy gain; these tumors were highly enriched for ABC-type DLBCLs. This coordinate signature and additional alterations of p53 pathway components were associated with outcome. We explored bases for the identified genetic alterations in DLBCL by performing an in silico mutational signature analysis. The most frequent mutational signatures were those of spontaneous deamination (aging) and AID with rare cases of microsatellite instability. We also assessed the clonality of identified genetic features to define cancer cell fraction and establish the timing of specific genetic events. The comprehensive genetic signatures of clinically annotated DLBCLs provide new insights regarding approaches to targeted therapy. Disclosures Link: Kite Pharma: Research Funding; Genentech: Consultancy, Research Funding. Rodig:Perkin Elmer: Membership on an entity's Board of Directors or advisory committees; BMS: Research Funding. Pfreundschuh:Boehringer Ingelheim, Celegene, Roche, Spectrum: Other: Advisory board; Roche: Honoraria; Amgen, Roche, Spectrum: Research Funding. Shipp:Gilead: Consultancy; Sanofi: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Programmed death 1 (PD-1) is a T cell co-inhibitory receptor with two ligands, PD-L1 and PD-L2. In B-cell malignancies, this pathway plays a major role in immune resistance in the tumor environment by promoting the differentiation of regulatory T-cells and inducing T-cell exhaustion. Recent data have shown that blockade of this pathway can enhance antitumor immune responses. While interactions between PD-1 and its ligands have been studied in various lymphoid tissues, little data exist regarding these interactions in the bone marrow, particularly in patients with Waldenstrom macroglobulinemia (WM). The goal of this study was therefore to determine the expression of PD-1 and its ligands in the bone marrow of patients with WM and to assess the functional role of PD-1 signaling in this disease. Using immunohistochemistry, the expression of PD-1, PD-L1 and PD-L2 in bone marrow (BM) specimens from patients with WM (n=6) was compared to normal control BM. PD-1 expression was modest and the pattern of staining in WM was similar to normal BM. In contrast however, intense staining for PD-L1 and PD-L2 was seen in WM compared to controls. When analyzed by flow cytometry, PD-L1 and PD-L2 expression was seen on malignant B-cells and also on dendritic cells, monocytes and macrophages isolated from the bone marrow. To determine the functional effect of PD-1 signaling in WM, we stably transfected PD-L1 and PD-L2 into the HEK-293 cell line. The WM cell lines, MWCL-1, BCWM.1 and RPCI-WM1 as well as patient specimens, were then cocultured with either the PD-L1 or PD-L2 expressing HEK-293 cells. When compared to cells expressing an empty vector control, proliferation and viability of WM cells was increased when they were cocultured with cells expressing PD-L1 or PD-L2. Addition of blocking antibodies abrogated the increase in proliferation. These results show that PD-L1 and PD-L2 are highly expressed on both malignant B-cells and non-malignant cells within the BM microenvironment in WM and promote malignant B-cell growth. Inhibition of PD-1 signaling may therefore be a promising therapeutic strategy in patients with WM. Disclosures: No relevant conflicts of interest to declare.

Abstract Peripheral T- and NK-cell lymphomas (PTCLs) are fatal in the majority of patients, and conventional chemotherapy is minimally effective. Targeted inhibition of tyrosine kinases (TKs) might be a useful treatment strategy, but TK overexpression by PTCLs has not been well characterized (except ALK). Recently a novel translocation t(5;9) fusing the ITK and SYK genes was reported in a subset of unspecified-type PTCLs, associated with high SYK gene expression and Syk protein positivity. Syk is a non-receptor TK important in immunoreceptor signal transduction, providing proliferation and survival signals in a variety of hematopoietic cells. Syk is absent or expressed at very low levels in most normal post-thymic T cells, where this signal transduction role is fulfilled by ZAP70. Since Syk TK inhibitors are now in clinical trials for other diseases, we sought to determine the incidence of t(5;9) and Syk overexpression in PTCL. Tissue microarrays were constructed using triplicate cores from paraffin-embedded tissue blocks. Cases were studied using fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Additional studies were performed using flow cytometry and Western blot. There were 141 PTCLs, including 35 angioimmunoblastic, 66 unspecified, 21 anaplastic large cell, 2 enteropathy-associated, 5 hepatosplenic, 5 extranodal NK/T, and 7 other. No evidence of t(5;9) was identified by FISH in 86 informative cases. Normal T-cell subsets from peripheral blood, spleen, and lymph node were negative for Syk by IHC, flow cytometry, and Western blot. Syk was positive by immunohistochemistry in 133 of 141 (94%) PTCLs. All 8 Syk negative cases were extranodal, cytotoxic PTCLs. Western blot on frozen tissue correlated with IHC results in paraffin. All 4 Syk-positive cases tested showed phosphorylation of tyrosine residues 525/526, known to be required for Syk activation. We conclude that Syk is overexpressed in most PTCLs, including the vast majority of nodal cases. Syk may substitute for ZAP70 in these tumors and provide ongoing proliferation and survival signaling. The overexpression of Syk and phosphorylation of its Y525/526 residues suggest Syk may be a suitable target for pharmacologic TK inhibition as a treatment option for patients with PTCL.

Abstract Background: While B-cell receptor (BCR) signaling is essential for the development, of normal B cells, its aberrant hyper-activation results in neoplastic transformation of B-lymphocytes. Recent investigations using small molecule inhibitors validate the BCR pathway as a valuable target. Bruton’s tyrosine kinase (BTK) is one of the components of a signaling hub that transduces signals from the BCR into the cell for its activation and has been shown to be a therapeutic target. Ibrutinib (PCI-32765), an irreversible BTK inhibitor has shown clinical efficacy in CLL, mantle cell lymphoma (MCL) and Waldenströms macroglobulinemia (WM). Ibrutinib binds to cysteine-481 of the BTK protein and blocks its phosphorylation, resulting in termination of BCR-mediated activation of cells with a concomitant induction of death. Despite the clinical success of ibrutinib, a high percentage of patients achieve only partial response and eventually acquire resistance to the drug, resulting in aggressive relapse of the disease. A mutation of Cys481-Ser in BTK (ibrutinib-BTK binding site) has been reported to be one of the reasons for the development of ibrutinib resistance (IR). To understand the mechanisms resulting in acquisition of IR, we developed preclinical models of IR in WM and MCL. Materials: Ibrutinib was obtained from Pharmacyclics, CA. Validated human WM models (BCWM.1, RPCI-WM1 and MWCL.1 cell lines) and human MCL models (Jeko-1 and Maver cell lines) were used for the study. Results: BTK was constitutively phosphorylated at Y223 and Y551 in all the cell lines tested and this was inhibited by ibrutinib in a dose dependent manner. Phosphorylation of other kinases in the cascade such as SYK (Y323 and Y525/526) and PLCg2 (Y759 and Y1217) were also inhibited while AKT phosphorylation at both Ser473 and Thr308 was consistently increased in presence of ibrutinib. Treatment with ibrutinib induced cell cycle arrest in the G1 phase by 24h followed by apoptosis. Cell growth assays (MTS assay) showed that BCWM.1 was the most sensitive cell line followed by MWCL-1, RPCI-WM1, Maver and Jeko-1. Exposure of WM and MCL cells for prolonged periods of time with progressively increasing concentrations of ibrutinib resulted in outgrowth of clones (IR WM and MCL cell lines) that were resistant to apoptosis with a slow growth rate as compared to wild type parental cells. IR cells attained 2 – 20 fold resistance to ibrutinib as compared to the respective parental lines as determined by MTS assay. Sequence analysis of the BTK gene in all the cell lines revealed no mutation in IR cells at Cys481 suggesting that in an acquired IR state, resistance to ibrutinib can be developed independent of BTK Cys481 mutation. Interestingly, we found p-BTK levels to be markedly reduced in IR cells. Ibrutinib reversal experiments suggested that while a continuous presence of ibrutinib is needed for inhibition of BTK phosphorylation, a stable IR state could be maintained (for >1 month) in the absence of ibrutinib. This suggested the cells reliance on a parallel survival pathway, independent of BTK phosphorylation. Focused mRNA (Nanostring nCounter assay) and immunoblot analysis revealed significant changes in the expression profiles of several cellular elements. These included transcription factors such as PU.1, IRF4, BLIMP1, BCL-6 b-catenin as well as the phosphorylated ERK1/2, STAT1 and 3 suggesting a reprogramming of critical cellular networks, which IR tumor cells might be utilizing to overcome ibrutinib-induced cytotoxicity. Importantly, we observed that IR cells retained high levels of p-AKT and showed an increase in expression of BCL2 family members, as well as BCL-2 itself. Treatment of IR cells with ibrutinib +/- MK2206 (AKT inhibitor), or ABT-199 (BCL-2 inhibitor), synergistically induced cytotoxicity in IR cells, suggesting the importance of these parallel survival pathways (AKT/BCL2) in maintaining an IR state. Conclusion: Here we demonstrate that in the absence of BTK Cys481 mutation, an IR state is associated with reprogramming of transcriptional networks countering ibrutinib-induced toxicity by activation of AKT and BCL-2. Our current data exposes multiple vulnerabilities within IR cells, which can be therapeutically exploited to potentially delay onset of IR, by targeting alternative oncogenic mechanisms that are activated in presence of sustained BTK inhibition. Disclosures No relevant conflicts of interest to declare.