Price-Troska, Tammy

Abstract Waldenstrom's Macroglobulinemia (WM) is an indolent B-cell malignancy that is characterized by bone marrow infiltration of lymphoplasmacytic cells and excessive synthesis of IgM. Despite improved treatment strategies and increased understanding of the underlying molecular mechanisms contributing to malignant disease progression, WM remains incurable. While whole exome sequencing analysis has revealed the genomic events associated with malignant B cell transformation in WM, the bone marrow (BM) microenvironment is also emerging as a major player in the pathogenesis of WM. Previously, our lab has reported that an array of cytokines, including IL-21 and IL-6 are increased in the WM BM and such increases are associated with high proliferation rates and IgM secretion by WM cells. In this study, we aimed to identify how immune checkpoint molecules in the BM microenvironment, specifically programmed cell death-1 (PD-1) and its ligands PD-L1 and PD-L2, contribute to malignant cell expansion in WM. Using Real-Time PCR analysis, we show that the expression of PD-1, PD-L1 and PD-L2 are all significantly elevated in the cells of WM BM as compared to their normal BM counterparts. Interestingly, PD-L1 expression is also upregulated in the malignant WM cells. These findings were further confirmed by flow cytometry analysis. Subsequent in vitro analysis showed that PD-L1 and PD-L2 are cleaved from the WM cells and these soluble ligands (sPD-L1 and sPD-L2) are able to bind to the cells in the BM microenvironment, including T-cells. This results in reduced activation and proliferation of T-cells, and is accompanied by a reduction in cyclin A and p-ERK levels. In validation of the in vitro data, we also found sPD-L1 and sPD-L2 in the bone marrow plasma obtained from WM patients. While sPD-L2 was found to be present in both WM and normal BM plasma (though in a reduced level in WM), sPD-L1 was exclusive to the WM samples, implying that the function of these molecules are differentially regulated in WM. Furthermore, overexpression of PD-L1 in a WM cell line, MWCL.1, resulted in an increase in IgM secretion. Interestingly, treatment with IL-21 increased the expression of PD-L1 in WM cells, indicating that elevated IL-21 in WM BM could contribute to increased expression of PD-L1 by malignant WM cells. In summary, our data support a role for PD-1 ligands as immune regulatory molecules in WM. Further studies are ongoing to explore the molecular mechanisms by which PD-1/PD-L1/PD-L2 signaling affects the pathophysiology of WM cells. Disclosures No relevant conflicts of interest to declare.

Abstract While extensive, the genetic studies of DLBCL tumors to date have primarily focused on somatic mutations that are associated with development of lymphoma, i.e., driver mutations. Identification of key genetic events that impact and/or predict response to therapy and clinical outcome of lymphoma patients has not been accomplished. In an exploratory study, we used whole-exome sequencing to identify novel biomarkers that can predict which patients have an aggressive form of DLBCL, and therefore would likely benefit from a different and more aggressive treatment plan. Using whole-exome sequencing data from 54 newly diagnosed DLBCL patients, we evaluated the association of somatic coding single nucleotide (cSNV) and copy number (CNV) variants with aggressive DLBCL. All patients were treated with R-CHOP or immunochemotherapy, and disease aggressiveness was based on relapse, with patients classified as having aggressive disease (AD) (n=13, defined as treatment failure, relapse, or progression within 24 months of diagnosis) versus non-aggressive disease (n=41, defined as achieving at least 24 months of relapse-free survival). An in-house algorithm, patternCNV was used to detect somatic CNVs. Logistic regression was used to assess statistical significance. In the cSNV analysis, 24 genes were found to be significantly (p ≤ 0.05) associated with AD. Of these genes, CIITA (p=0.01) was previously identified as a mutational target in DLBCL and is a recurrent gene fusion partner in lymphoid cancers. Metacore analyses showed that seven of these genes, including CIITA, can be placed in the same regulatory network centered around CREB1. Interestingly, the CREB binding protein (CREBBP) is a known target of pathogenic mutations in DLBCL. In the CNV analyses, we identified 245 gene amplifications and 209 gene deletions associated with AD (p ≤ 0.05). Deleted genes were localized in three major chromosomal regions, 6p22.3-6p22.1 (26 genes), 6q13-6q16.3 (31 genes), and 6q21-6q24.2 (86 genes). In the CNV amplification analysis, the genes were localized in two major chromosomal regions, 3q12.3-3q29 (90 genes) and 19q13.12-19q13.43 (122 genes). We also quantified the association of each regional deletion/amplification with patient outcome. As expected, each deleted region was univariately associated with time to relapse: 6p22.3-6p22.1 (HR = 7.19, 95% CI: 2.66-19.46, p=1.33x10-5), 6q13-6q16.3 (HR = 4.44, 95% CI: 1.74-11.32, p=6.84x10-4), and 6q21-6q24.2 (HR = 5.42, 95% CI: 2.12-13.87, p=9.23x10-5) as well as the two amplification regions: 3q12.3-3q29 (HR = 4.60, 95% CI: 1.49-14.24, p=4.27x10-3) and 19q13.12 -19q13 (HR = 13.79, 95% CI: 4.39-43.34, p=2.81x10-8). Deletions at 6q21-6q24.2 have been previously reported in DLBCL and two tumor suppressor genes associated with lymphoma pathogenesis are localized in the region, TNFAIP3 (p=0.14) and PRDM1 (p=0.02), the latter of which was significantly associated with AD. However, the genes in the 6p21 locus that were most significant (p=0.002) were SLC22A16, GPR6, SOBP, MATTL24, DDO, and REV3L. SLC22A16, which also had cSNVs in two tumors, is an organic cation transporter that has been shown to transport chemotherapeutic drugs including doxorubicin. Successful drug response has been correlated with the level of activity and expression of this transporter in tumor cells. To determine if expression of SLC22A16 would have an impact on doxorubicin transport, and may therefore impact response to R-CHOP we overexpressed either an empty vector control or SLC22A16 in OCI-Ly7 DLBCL cells, which do not express endogenous SLC22A16 mRNA. We found that OCI-Ly7 cells expressing SLC22A16 have increased 14C-doxorubicin uptake and are more sensitive to doxorubicin-induced cell death when compared to the empty vector control cells. These data suggest that loss of SLC22A16 expression through gene deletion could impact the ability of DLBCL cells to respond to therapy and indicates an aggressive form of the disease. In summary, our data are the first to use whole exome sequencing to identify genetic variants associated with aggressive DLBCL, which will require replication in additional samples. Nevertheless, our data highlight the role for somatic CNVs in patient outcome and we biologically validate the potential impact of deletions in SLC22A16 at 6p21. Disclosures: No relevant conflicts of interest to declare.

Abstract T-cell exhaustion plays an important role in attenuating the function of immune cells in B-cell non-Hodgkin's lymphoma (NHL) and PD-1 expression is typically used to identify exhausted T-cells. We have however previously shown that not all PD-1+ cells are exhausted and that PD-1 is differentially expressed on two distinct T-cell subpopulations, with high expression on T follicular helper cells and dim expression on exhausted T cells. Other markers are therefore needed to more clearly identify exhausted intratumoral T cells. To further define exhaustion of intratumoral T cells, we determined the co-expression, regulation and function of PD-1, TIM-3 and LAG-3 on CD4+ or CD8+ T cells by flow cytometry. Using biopsy specimens from follicular B-cell NHL, we found that the percentages of PD-1+ and TIM-3+ T cells were 53.1% (range: 17.2-81.2%, n=32) and 34.5% (range: 14.9-62.6%, n=34) in CD4+ T cells and 46.8% (range: 12.8-81.7%, n=32) and 40.4% (range: 15.0-78.4%, n=34) in CD8+ T cells, respectively. We observed that TIM-3 was predominantly expressed on PD-1dim T cells and TIM-3+ cells accounted for 40% of CD4+ PD-1dim or 45% of CD8+ PD-1dim T cells. Similarly, LAG-3 was variably expressed on intratumoral T cells from B-cell NHL. A median of 9.54% (range: 3.01-15.46, n=6) of CD4+ or 20.48% (7.93-33.9, n=8) of CD8+ T cells express LAG-3. We found that LAG-3+ T cells almost exclusively came from PD-1+ TIM-3+ cells, forming a defined population of intratumoral PD-1+ TIM-3+ LAG-3+ CD4+ or CD8+ T cells. While the majority of LAG-3+ T cells were effector memory T cells (CD45RA- CCR7-), some LAG-3-expressing T cells displayed a phenotype of terminally-differentiated T cells (CD45RA+ CCR7-). Functionally, the intratumoral TIM-3+ LAG-3+ T cells exhibited reduced capacity to produce cytokines (IL-2, IFN-γ) and granules (perforin, granzyme B). Similar to TIM-3, LAG-3 expression was strongly up-regulated on CD4+ or CD8+ T cells by IL-12, a cytokine that has been shown to induce T-cell exhaustion. Interestingly, we observed that while expression of TIM-3 on CD8+ T cells was upregulated by IL-12 at an early time point (day 1), LAG-3 was only induced after TIM-3 up-regulation (day 3) and almost exclusively on TIM-3+ T cells. Furthermore, we found that blockade of both TIM-3 and LAG-3 signaling was able to reverse the exhausted phenotype of CD8+ T cells resulting in increased IFN-γ and IL-2 production. This effect was further enhanced when CD8+ T cells were treated with both anti-TIM-3 and anti-LAG-3 Abs. Taken together, these results suggest that PD-1, TIM-3 and LAG-3 were involved in the induction of exhaustion of T cells in B-cell NHL. We find that PD-1, TIM-3 and LAG-3 are expressed on the same T cells and that blocking TIM-3 and LAG-3 can reverse T-cell exhaustion signaling. These results suggest that PD-1, TIM-3 and LAG-3 play a synergistic role in the development of T cell exhaustion in NHL. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 2699 Myeloid differentiation factor 88 (MYD88) is an adaptor protein that plays a key role in mediating innate immune response. Upon activation of toll-like (TLRs) or IL-1b receptors, MYD88 activates a signaling cascade that culminates in activation of NF-kB and expression of proinflammatory genes. Activating mutations in MYD88 have been reported in non-Hodgkin's lymphoma (NHL) tumors, including diffuse large B cell and marginal zones lymphoma. The most common MYD88 mutation described thus far is a single base pair mismatch resulting in an amino acid switch from lysine to proline at position 265 (MYD88L265P). MYD88L265P functions as a constitutively active MYD88 protein resulting in dysregulated NF-kB and STAT3 signaling. This mutation has recently been reported to be present in lymphomoplasmacytic lymphoma/Waldenstrom macroglobulinemia (LPL/WM) at a high frequency, ∼ 90% (Xu et al, ASH, #261, 2011). The discovery of MYD88L265P in a high percentage of LPL/WM tumors, and other subtypes of NHL, provides the basis for the identification and targeting of MYD88 dependent pathways. Additionally, the ability of this mutation to drive NF-kB-mediated cytokine expression combined with our finding that LPL/WM patients have elevated serum cytokines suggests that the MYD88 mutation may play a significant role in LPL/WM pathogenesis. We first wanted to confirm the incidence of the MYD88L265P mutation in LPL/WM and other subtypes of indolent lymphoma. Using Sanger sequencing we found that 57% (n=58) of LPL, 4% of MALT (n=23), 5% of nodal marginal zone (n=34), and 6% of splenic marginal zone (n=34) lymphomas harbor the MYD88L265P mutation, with all but 1 case being heterozygous. When we specifically looked at the LPL cases with WM, we found that 70% of WM tumors have the MYD88L265P mutation. In a validation cohort of WM (n=41), we found a similar mutation rate of 68%. Additionally, the WM cell line MWCL1 and the IgM secreting cell line BCWM.1 also harbor the MYD88L265P mutation. The prevalence of the MYD88L265P mutation in NHL, specifically WM and LPL, suggests that it may be a novel driver of lymphoma pathogenesis and a potential therapeutic target. However, it is not yet clear if this mutation correlates with activation of signaling pathways, or cell growth and survival in LPL/WM. To address these questions we first explored the possibility that the MYD88 signaling pathway is constitutively active in cells that express MYD88L265P. Upon activation of TLRs or IL-1b receptors, MYD88 forms a homodiamer and recruits IRAK1/4 and TRAF6 into a complex resulting in association and phosphorylation of TAK1 followed by activation of NF-kB. Using three cell lines that express MYD88L265P (BCWM, MWCL1, and OCI-Ly3), we looked for complex formation of MYD88, IRAK1/4, TRAF6, and TAK1. Immunoprecipitation of either endogenous IRAK1 or TAK1 revealed constitutive association with both TRAF6 and MYD88. We also detected phosphorylation of TAK1, and taken together, these data suggest that the MYD88 pathway is activated in cells that harbor the MYD88L265P mutation. We next wanted to confirm the significance of the MYD88 pathway on lymphoma cell growth. Using our cell lines we tested the effect of IRAK1/4, TAK1, and NF-kB inhibitors on cell proliferation. All MYD88L265P expressing cell lines were sensitive to the TAK1 and NF-kB inhibitors in a dose dependent manner (0–10 uM), however, we only saw inhibition of cell proliferation with the IRAK1/4 inhibitor at the highest dose (10 uM) in the BCWM cell line. These data suggest that cell proliferation is dependent on the MYD88 signaling pathway, with some variation being detected between cell line models and inhibitors. Because the MYD88 pathway has also been shown to drive cytokine secretion we next tested the impact of the IRAK1/4, TAK1, and NF-kB inhibitors on expression of IL-10. Using drug doses that were shown to inhibit cell proliferation, but not impact survival, we found that all three inhibitors reduced the level of IL-10 secreted by each of cell lines. In summary, our data confirm the high incidence on the MYD88L265P mutation in LPL/WM, we find that the MYD88 signaling pathway is constitutively activated in cells the harbor the mutation, and we show that cell proliferation and cytokine secretion are dependent on MYD88 signaling targets. These studies highlight the biologic significance of the MYD88L265P mutation in LPL/WM and suggest that the MYD88 signaling pathway may be a novel therapeutic target. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 468 The requirement for BAFF and BAFF-R in normal human and murine B cells is well studied, but there is also significant evidence to suggest that BAFF plays an important role in malignant B cell proliferation and survival. Serum BAFF levels are elevated in patients with non-Hodgkin lymphoma (NHL) and high BAFF levels correlate with aggressive disease and a poor response to therapy. There is also increasing genetic evidence suggesting an association between the development of human disease and genetic variation in genes encoding BAFF and its receptors. Mutations in TNFRSF13B (TACI) were identified in patients with familial common variable immunodeficiency (CVID) and IgA deficiency and we have found that single nucleotide polymorphisms (SNP) in TNFSF13B (BAFF) are associated with elevated BAFF levels and risk for developing NHL. To build upon these findings we sequenced BAFF and its receptors; TNFSF13B, TNFRSF13B, TNFRSF17(BCMA), and TNFRSF13C (BAFF-R) in NHL patients to identify novel genetic variants that may be associated with NHL risk. Among 40 individual samples (20 controls and 20 follicular lymphoma (FL) cases) that were bi-directionally sequenced we identified a heterozygous cytosine to thymidine transition in 1 patient specimen at position 475 (C475T) of TNFRSF13C. The C475T transition encodes a missense substitution of tyrosine for histidine in codon 159 (H159Y) in the highly conserved cytoplasmic tail of BAFF-R, adjacent to the TRAF3 binding motif PVPAT. We next expanded our analysis of BAFF-R H159Y and analyzed NHL tumor biopsies for the presence of the mutation. 4/41 (10%) follicular lymphomas (FL), 2/42 (5%) diffuse large B cell lymphomas, 1/22 (5%) lymphoplasmacytic lymphomas (LPL), and 1/24 (4%) mucosal associate lymphoid tissue lymphomas carried the heterozygous mutation. The BAFF-R H159Y mutation was not detected in any of the normal control DNA from healthy donors (n=100). Given its close proximity to the TRAF3 binding site in the cytoplasmic domain of BAFF-R we first wanted to determine if the H159Y mutation altered BAFF induced signaling. We generated cell lines that express HA-tagged wildtype BAFF-R, BAFF-R with the H159Y mutation, or BAFF-R with an ablated TRAF3 binding site as a negative control. Analysis of cells expressing H159Y BAFF-R demonstrates that this mutation results in increased BAFF-R-mediated NFκB1 and NF-κB2 activation. The enhanced signal activated by BAFF-R H159Y is coupled with a several fold increase in TRAF3, TRAF2, and TRAF6 recruitment to BAFF-R and increased IgM production. We further demonstrate that recruitment of TRAF6 to BAFF-R is not unique to the mutant H159Y BAFF-R, but is also an important and necessary feature of BAFF-R signaling in normal B cells. Collectively, our data identify a novel lymphoma-associated mutation in BAFF-R and describe exciting new aspects of BAFF-R signaling that are important for understanding normal B cell homeostasis and function, as well as pathogenic BAFF-R contributions to human disease. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 1999 Recurrent chromosomal translocations involving the IGH locus are characteristic of B-cell non-Hodgkin lymphoma (NHL) and MALT lymphoma in particular has been pathologically characterized by specific IGH translocations. However, these translocations are present in only a subset of cases, suggesting that additional uncharacterized translocations might exist. In previous studies we characterized the novel t(X;14)(p11.4;q32) translocation in a patient with MALT lymphoma and found that GPR34, an orphan G-protein coupled receptor (GPCR), was highly expressed due to its juxtaposition to the IGHSA2 switch region. Although the t(X;14)(p11;q32) translocation was only identified in one patient, we wanted to determine its expression across a spectrum or normal and malignant lymphoma tissue, as other mechanisms may contribute to overexpression of genes. We measured GPR34 mRNA expression by quantitative PCR in tissue biopsies from a panel of lymphomas. As controls, we also measured GPR34 mRNA expression in normal resting or activated CD19+ B cells, resting and activated CD3+ T cells, and CD14+ monocytes. Expression of GPR34 was significantly increased in MALT (37-fold, n=35), LPL (23-fold, n=23), nodal marginal zone B cell lymphoma (18-fold, n=21), and splenic marginal zone B cell lymphoma (21 fold, n=33) compared to resting CD19+ B cells (n=11). In a gastric MALT lymphoma specimen we detected GPR34 expression at levels similar to the t(X;14)(p11;q32) patient and interphase FISH studies showed an extra intact GPR34 signal, but no translocation involving IGH or GPR34, suggesting that other mechanisms, including gene dosage effect, can upregulate GPR34. The receptor encoded by GPR34 is most similar to the PY2 receptor subfamily of GPCRs and signaling studies suggest that overexpression of GPR34 results in an accumulation of inositol phosphates and MAP-kinase activation. To further characterize the impact of GPR34 overexpression on cell signaling, HeLa cells were transduced with WT GPR34, a signaling deficient GPR34 (GPR34 DRY), or a vector control. To determine if MAPK activity was upregulated, the phosphorylation status of ERK1/2 in GPR34 WT, GPR34 DRY, and vector control cells was analyzed and we found that ERK1/2 was constitutively phosphorylated at higher levels (1.6-fold) in GRP34 WT cells compared to GRR34 DRY or vector control cells. To further explore which signaling pathways were affected by GPR34 overexpression, GPR34 WT or vector control cells were transfected with an AP-1, CRE, NF-kB, E2F, SRE, NFAT, or ISRE- luciferase reporter plasmid. GPR34 expressing cells had increased luciferase activity driven by AP-1 (5.35-fold), CRE (4.7-fold), NF-kB (2.6-fold), and E2F (2.1) when compared to vector control cells. GPR34 DRY was unable to activate these pathways. AP-1 and CRE have been implicated in a large variety of cellular processes, including transformation, and both AP-1 and CRE activity is induced upon activation of MAP kinases. In untreated cells, both AP-1 and CRE activity were significantly higher in GPR34 WT cells compared to GPR34 DRY cells and both AP-1 and CRE luciferase activity was inhibited by the MEK1 inhibitor PD98059, suggesting that activation of these pathways is MAP-kinase dependent. To determine the biologic impact of GRP34 overexpression, the proliferation rates of vector control, GPR34 WT, and GPR34 DRY cells were compared and we found that proliferation of GPR34 WT cells was significantly higher (5.6-fold) than that seen in GPR34 DRY cells. We next tested the effect of the MEK inhibitor on proliferation and saw a dose dependent decrease in proliferation of GPR34 WT expressing cells. These results suggest that GPR34-mediated proliferation is dependent on MAPK. The presence of elevated GPR34 expression in tumors and the increased proliferation mediated by GPR34 suggests that it may have oncogenic potential. We therefore tested the ability of GPR34 WT cells to generate tumors in a tumor colony-forming assay. Only the GRP34 WT cells had the ability to form tumors in soft agar suggesting that overexpression of GPR34 can result in tumor formation. Taken together, our results identify a novel translocation in MALT lymphoma, emphasize a novel role for GPR34 in tumor cell growth, and suggest that MEK inhibitors may be useful in a subset of translocation-harboring or GRP34 high-expressing tumors. Disclosures: Fonseca: Genzyme: Consultancy; Medtronic: Consultancy; BMS: Consultancy; AMGEN: Consultancy; Otsuka: Consultancy; Celgene: Consultancy, Research Funding; Intellikine: Consultancy; Cylene: Research Funding; Onyx: Research Funding; FISH probes prognostication in myeloma: Patents & Royalties.

Abstract Plasma cell leukemia (PCL) is an aggressive and rare hematological malignancy that can originate either as primary disease (pPCL) or as a leukemic transformation of multiple myeloma (MMLT). We report here on the clinical characteristics, survival and genetic studies of 80 patients with PCL treated at a single institution (including 41 with pPCL and 39 with MMLT) and make comparisons with 439 newly diagnosed cases of multiple myeloma (MM). From our results pPCL presents a decade earlier than MMLT (54.7 vs 65.3 years) and despite substantially poorer clinical and laboratory parameters at presentation (hepatomegaly 32% vs 11%, leukocytes 31.6 vs 20.9, β2M 8.5 vs 4.3) pPCL appears more responsive to conventional combination chemotherapy (VAD, VBMVP or VBAP) than MMLT and is associated with significantly longer survival (median 18.4 vs 3 months). Comparison of pPCL groups treated with combination chemotherapy (n=21) or with other regimens (40% MP, 10% Thal/Dex, 20% other, 30% none)(n=20) identifies no substantial pre-treatment differences between the groups although a higher proportion of patients who received combination chemotherapy subsequently proceeded to stem cell transplantation (30 vs 10%). Importantly, survival of pPCL patients treated initially with combination chemotherapy (median 13.9, mean 27.3 months) was significantly longer compared with patients who did not receive combination chemotherapy (median 5.2, mean 9.9 months)(p=0.035) with 2 long term survivors (> 7 years) in the chemotherapy group. By comparison, patients with MMLT received less active therapy for their leukemic disease than did patients with pPCL (21% VAD, VBMVP or VBAP; 18% MP). Treated MMLT patients showed selection bias for younger age (60.9 vs 66.4 years) and lack of bone disease (0 vs 65%)(p<0.01); however despite this, median survival was disappointingly short for MMLT patients in the treatment group and was not significantly improved compared with non-treated patients (2.3 vs 0.8 months)(p=0.34). Assessment of novel therapies in PCL is therefore urgently required. Karyotype analysis and targeted genetic studies demonstrate that IgH translocations are present with high frequency in both pPCL and MMLT (71 vs 86%) compared with MM (~50%). Notably, IgH translocation in pPCL is almost exclusively targeted at chromosome 11 (cyclin D1) belying its importance in establishing the phenotype. IgH translocation in MMLT is primarily to chromosome 11 [71%], but also targets chromosomes 4 (FGFR3/MMSET) [13%] and 16 (cMaf) [20%], recapitulating MM. Abnormalities of chromosomes 3,5,7,9,11,13,15 and 19 are present equally in all 3 disorders. Deletion of 17p13 (p53) shows strong selection pressure in the leukemias (pPCL 53.8%, MMLT 48.8%, MM 10.7%) and is complemented by p53 mutation (23%). Notably, pPCL tumors show lower rates of Ras mutation (12 vs 40%) and p14 (0 vs 31%) or p16 (25 vs 40%) promoter methylation than MMLT. Together these results therefore indicate that pPCL and MMLT are fundamentally different plasma cell disorders with distinctive biology, genetic abnormalities and treatment responses.

Abstract The t[4;14] simultaneously deregulates fibroblast growth factor receptor 3 (FGFR3) and MMSET in 15% of patients (pts) with Multiple Myeloma (MM). Although oncogenic, FGFR3 expression is lost in ~25% of t[4;14] pts on gene expression profiling while MMSET is always retained. The t[4;14] is highly associated with poor prognosis, furthermore FGFR3 kinase inhibitors are in Phase I trials, thus detection of t[4;14] pts is increasingly important. The Multiple Myeloma Research Consortium (MMRC) therefore evaluated 4 competing methodologies for the diagnostic detection of t[4;14]. Bone marrow (BM) samples were collected in uniform fashion from 85 pts. FGFR3 immunocytochemistry (ICC) and flow cytometry (FC) were performed at the retrieval site, while split samples were shipped to the MMRC tissue bank and processed under GLP conditions. Processed samples were analyzed by cIg-FISH and quantitative IgH-MMSET RT-PCR (QPCR) on unsorted BM and blood. Of 60 samples with sufficient plasma cells for analysis, 8 were FISH +ve [13.3%]. Low % BM plasma cells prevented successful FISH in 25% of samples reflecting large volume harvests and hemodilution. Analysis was conducted in a blinded fashion. With FISH as the gold standard for detection of t[4;14] the sensitivity and specificity of the other diagnostic tests are: BM QPCR is most sensitive (7 of 8 FISH positive detected) and specific (42/43 negatives correctly identified). QPCR on peripheral blood is ongoing. FC is more sensitive to the detection of FGFR3 protein than ICC. Correlation between FC and ICC was only 0.46. Interestingly, 6 of 7 evaluable pts here and 13/14 (92%) in an expanded analysis of FISH +ve patients also expressed the FGFR3 protein. Given the discrepancy between this finding and previously reported loss of FGFR3 expression in 25% of pts we further explored t[4;14] stability. Clonal selection/heterogeneity was determined by the % plasma cells in each pt. with an unbalanced translocation (loss of one der chromosome). In 42 t[4;14] pts, 13 (31%) had a balanced translocation(>75% of cells with a double fusion), 14 (33%) had an unbalanced translocation (>75% cells with only one signal), and 15 (36%) had a chimeric picture. This heterogeneous pattern is suggestive of an evolution towards an unbalanced translocation. Despite this survival did not differ between pts with balanced or unbalanced translocation. Conclusions: These results indicate that the t[4;14] is highly heterogeneous with respect to balanced versus unbalanced translocations, which likely evolve over time. For detection, cIg-FISH continues to be the gold standard diagnostic methodology but may be limited by low plasma cell numbers in dilute BM or during MM remission. QPCR and FC appear most sensitive and specific for presence of t[4;14] and FGFR3 protein expression respectively. Surprisingly (given prior evidence of loss of FGFR3 expression in 25% of pts) 92% of t[4;14] pts in this series expressed FGFR3 protein. # Analyzed % Positive Sensitivity Specificity FISH 60 13 - - QPCR 65 14 87.5 97.6 Flow 82 15 85.7 91 ICC 85 15 62.5 92

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 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.