Hodge, Lucy S.

Abstract Although extensively studied, the exact mechanism by which TGF-β mediates T-cell inhibition is not entirely clear. When we examined the effect of TGF-β on the phenotype and function of T cells, we noted that CD70 was significantly up-regulated by TGF-β. This surprising finding led us to explore the underlying mechanism by which TGF-β upregulates CD70 expression on T cells and to define the function of CD70+ cells in B-cell NHL. Interestingly, we observed that TGF-β preferentially induced CD70 expression on effector memory T cells while it predominantly up-regulated Foxp3 on naïve T cells. CD70 induction is Smad3-dependent and involves Stat5 signaling. CD70+ T cells were highly susceptible to TGF-β-mediated apoptosis and that transfection of Jurkat cells with the CD70 gene led to a significantly reduced survival. TGF-β-induced CD70+ T cells had a diminished response to immune stimulation associated with downregulation of co-stimulatory molecules CD27 and CD28. CD70-expressing T cells from biopsy specimens of patients with B-cell NHL failed to produce cytokines and displayed no signal transduction when stimulated. CD70-expressing T cells were highly represented in follicular NHL biopsy specimens and increased numbers of CD70+ cells correlated with an inferior patient outcome. These novel findings not only revealed a biological role for a TGF-β/CD70 axis in mediating immune inhibition, but also may lead to therapeutic approaches in patients with B-cell NHL.

Abstract Massively parallel sequencing analyses have revealed a common mutation within the MYD88 gene (MYD88L265P) occurring at high frequencies in many non-Hodgkin lymphomas (NHL) including the rare lymphoplasmacytic lymphoma, Waldenström’s macroglobulinemia (WM). Using whole exome sequencing, Sanger sequencing and allele-specific PCR, we validate the initial studies and detect the MYD88L265P mutation in the tumor genome of 97% of WM patients analyzed (n=39). MYD88L265P was detected at lower frequencies in other indolent lymphomas including LPL (0%), MALT (4%), nodal MZL (5%) and splenic MZL (8%); all but one MYD88L265P was heterozygous. Due to the high frequency of MYD88 mutation in WM and other NHL, and its known effects on malignant B cell survival, therapeutic targeting of MYD88 signaling pathways may be useful clinically. However, while the effects of MYD88L265P on the activity of IRAK1/4 and NF-κB are have been studied previously, we are lacking a thorough characterization of the role of intermediary signaling proteins such as TRAF6 and TAK1 on the biology of MYD88L265P-expressing B cells. A better understanding of the proteins involved in MYD88L265P signaling may lead to the development of more targeted and effective therapeutic approaches. In an attempt to identify MYD88L265P –specific therapeutic targets we first wanted to characterize the role of intermediary signaling proteins that facilitate the downstream activation of NF-κB. Upon activation of TLRs or IL-1b receptors, MYD88 forms a homodimer and recruits IRAK1/4 and TRAF6 into a complex resulting in association and phosphorylation of TAK1 followed by activation of NF-κB. We monitored the formation of a complex comprised of MYD88, IRAK1, IRAK4 and TRAF6 and immunoprecipitation of either endogenous IRAK4 or IRAK1 revealed constitutive association of IRAK with TRAF6 and MYD88L265P. To assess if the formation of a MYD88L265P/IRAK/TRAF6 complex results in downstream activation of TAK1, constitutive TAK1 phosphorylation was measured and detected in all three cell lines that express MYD88L265P. An association between TAK1 and TRAF6, another measure of TAK1 activation, was also detectable. When a similar analysis of TAK1 was performed in DLBCL cells expressing wild-type MYD88, no phosphorylation of TAK1 was detected, nor was TAK1 associated with TRAF6. IRAK1, IRAK4, TAK1, TRAF6, and MYD88 were expressed at similar levels in all cell lines studied and therefore did not contribute the differences in MYD88 complex formation observed between cell lines. These studies were further confirmed using HEK 293T cells that were transduced with either a vector control plasmid or HA-tagged MYD88WT or MYD88L265P expression plasmids. Together, these studies suggest that MYD88L265P forms a complex with IRAK and TRAF6 resulting in constitutive activation of TAK1 and NF-κB. To confirm the significance of TAK1-mediated MYD88L265P signaling on lymphoma cell growth, the effect of the selective TAK1 inhibitor, (5Z)-7-Oxozeaenol, on cell proliferation was tested. All MYD88L265P-expressing cell lines were sensitive to TAK1 inhibition in a dose-dependent manner (0-10 μM). In contrast, NHL cells expressing MYD88WT were found to be insensitive to TAK1 inhibition. We next tested the impact of the TAK1 inhibitor on a MYD88L265P positive WM patient sample. Similar to what was seen in the WM cell lines, the TAK1 inhibitor inhibited WM cell growth and survival in a dose dependent manner. Additionally, the TAK1 inhibitor significantly reduced the level of IL-10 secreted by each of the cell lines. Together, these data suggest that MYD88L265P drives cell proliferation and cytokine secretion through a TAK1-dependent mechanism. In conclusion, we are the first to validate by NGS in a large patient cohort the high prevalence and specificity of MYD88L265P in WM. Cells harboring the L265P mutation but not wild-type MYD88 exhibit constitutive signaling leading to the hyperactivation of NF-κB. We have established the role of TAK1 as an integral component of MYD88L265P signaling in both WM and DLBCL cell. Our data suggest that targeting TAK1 clinically may be an effective strategy for the treatment of WM and other lymphomas driven by MYD88L265P signaling. Disclosures: Fonseca: millennium: Consultancy; amgen: Consultancy; Binding site: Consultancy; onyx: Consultancy; medtronic: Consultancy; Genzyme: Consultancy; Otsuka: Consultancy; Celgene: Consultancy; lilly: Consultancy; Onyx: Research Funding; cylene: Research Funding.

Abstract Abstract 770 Background: Waldenstrom's macroglobulinemia (WM) is a B-cell lymphoma characterized by high serum monoclonal IgM and infiltration of lymphoplasmacytic cells into the bone marrow. As with many hematologic malignancies, cytokines within the tumor microenvironment play an important role in supporting the growth and survival of malignant WM cells. IL-21 is a pleiotropic cytokine involved in the differentiation of B cells into plasma cells. During malignancy, IL-21 has demonstrated diverse effects promoting the growth of myeloma and Hodgkin lymphoma cells while inducing apoptosis in chronic lymphocytic leukemia. However, the biologic significance of IL-21 has not been examined in WM. Our objective here was to assess the expression of IL-21 and its receptor in WM cells and to examine whether IL-21 contributes to the biology of WM. Results: When compared to normal bone marrows, immunohistochemistry revealed significant IL-21 staining in the bone marrow of patients with WM (n=5). To determine whether WM cells are susceptible to IL-21 in the microenvironment, expression of the IL-21 receptor (IL-21R) was assessed via PCR in CD19+CD138+ cells isolated by positive selection from patients with WM (n=8) and in the newly characterized WM cell line, MWCL-1. Nearly all (7/8) CD19+CD138+ WM cells expressed IL-21R, as did MWCL-1 cells. Using flow cytometry we detected expression of IL-21R protein on the surface of WM cells as well. The contribution of microenvironmental IL-21 to the biology of WM tumors was then examined. In MWCL-1 cells, IL-21 (100 ng/mL) increased proliferation by 37% (p=0.005) over untreated controls as determined by thymidine incorporation at 72 hr, and in primary WM cells, proliferation increased by nearly 50% (p=0.003). Interestingly, the immortalized B cell line, IM-9, responded to IL-21 with a significant decrease in proliferation, consistent with previous data indicating differential effects of IL-21 depending on the pathological status of the B-cell in question. IL-21 also significantly induced (p<0.0005) IgM secretion in WM as measured by ELISA (MWCL-1 5,956 +/− 393 ng/mL vs. 10,013 +/− 730 ng/mL; CD19+138+ WM 504 +/− 33 ng/mL vs. 811 +/− 32.5 ng/mL). Annexin/PI staining was used to assess viability, but no apoptotic effects were associated with IL-21 in WM. To better understand the mechanisms through which IL-21 increases cellular proliferation and IgM secretion in WM, we characterized STAT activation in response to this cytokine. In MWCL-1 cells, IL-21 significantly increased the phosphorylation of both STAT1 and STAT3, and to a lesser extent, STAT5. Treatment with a STAT3 inhibitor completely abolished the effects of IL-21 on cellular proliferation and IgM secretion suggesting IL-21 mediates its biologic activity through a STAT3-dependent mechanism. The expression of transcription factors involved in B-cell differentiation was also measured in MWCL-1 cells treated with IL-21. Both BLIMP-1 and Bcl-6 levels significantly increased upon addition of IL-21, whereas PAX5 was significantly decreased. IL-21 had no effect on the expression of XBP-1, which is involved in regulating Ig secretion, suggesting that the increase in IgM secretion in MWCL-1 cells may occur secondary to the increase in proliferation, as opposed to an actual increase in the production of IgM. Lastly, IL-21 significantly enhanced IL-10 secretion from MWCL-1 cells (669 +/− 152 pg/mL vs. 1,948 +/− 279 pg/mL, p=0.0002). While the interplay between IL-10 and IL-21 in WM remains to be examined, IL-10 is known to be involved in normal B-cell development and may have synergistic effects with IL-21 in malignant WM cells. Overall our data indicate that IL-21 in the bone marrow microenvironment significantly affects the biology of WM tumor cells through a STAT3-dependent mechanism. 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 Abstract 2688 Members of the signal transducers and activators of transcription (STAT) family of proteins function as secondary messengers mediating cellular responses to various cytokines. Aberrant activation of STAT5 protein has been implicated in the pathogenesis of hematologic malignancies due to the ability of these transcription factors to regulate genes involved in cellular proliferation and survival. The two highly homologous transcription factors collectively known as STAT5, namely STAT5A and STAT5B, display both redundant and distinct physiologic functions in non-malignant B cells. Yet, despite evidence suggesting independent functions for STAT5A and STAT5B in the pathophysiology of solid tumors, the precise roles of these isoforms in hematologic malignancies such as Waldenstrom's macroglobulinemia (WM) are not known. Initial immunohistochemical staining of WM bone marrow biopsies (n=6) revealed higher levels of STAT5 phosphorylation compared to bone marrows from normal controls (n=6). Additionally, phosphorylated STAT5 was highly expressed in CD19/CD138+ sorted cells obtained from the bone marrow of patients with WM (average ΔMFI compared to isotype control, 4.64 +/− 1.7, n=6) as determined by FACS analysis. Furthermore, western blotting demonstrated baseline STAT5 phosphorylation in both WM and IgM-secreting cell lines (MWCL-1 and BCWM-1, respectfully). The expression of other phosphorylated STAT proteins (1, 3, 4, and 6) was not detected. To better understand the overall role of STAT5 biologically in WM, MWCL-1 and BCWM.1 cells were treated with a specific inhibitor of STAT5, N′-((4-Oxo-4H-chromen-3-yl)methylene) nicotinohydrazide. Following 72 hours in culture, this inhibitor significantly decreased IgM secretion at lower doses when compared to controls (10 μM, MWCL-1: 9413 +/− 511 ng/mL vs. 6166 +/− 160 ng/mL, p<0.001; BCWM.1: 13,380 +/− 393 ng/mL +/− 10970 +/− 240 ng/mL, p<0.001) and nearly abolished IgM secretion at higher doses. Significant effects on proliferation and viability were also observed, but only at higher concentrations of drug where the specificity toward STAT5 may have diminished. To characterize the roles of the individual STAT5 isoforms in WM, we have developed doxycycline-inducible STAT5A-shRNA and STAT5B-shRNA and used these to create stable knockdowns in the MWCL-1 cell line. Addition of doxycycline to these cell lines for 72h nearly abolishes STAT5A or STAT5B protein expression, respectively, without affecting expression of the other isoform, while no change in STAT5 expression is detected in cells transduced with the empty vector (EV) control. The functional effects of isoform-specific STAT5 inhibition on WM tumor biology were assessed through proliferation assays and ELISA to determine the utility of therapeutically targeting a single STAT5 isoform. No difference in proliferation was observed in the STAT5A- or STAT5B-shRNA cells following 72h induction with doxycycline as compared to the EV control cells. However, specific knockdown of STAT5A following doxycycline induction significantly decreased IgM secretion as compared to the EV control (EV, 91.8 +/− 10.2% of baseline secretion, STAT5A, 66.7 +/− 15.1% of baseline, p<0.05), whereas IgM secretion was decreased by knockdown of STAT5B but not significantly. Similarly, IL-6 secretion was only diminished in cells lacking STAT5A as compared to EV cells (EV, 94 +/− 14.16% of baseline secretion; STAT5A, 64% +/− 7.6% of baseline, p<0.001). Overall these initial data indicate a role for isoform-specific STAT5 activation in the maintenance of WM tumors, and future studies will further our understanding of the specific roles of STAT5A and STAT5B in WM tumors. Disclosures: Ansell: Seattle Genetics, Inc.: Research Funding.

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 1554 T cells in the tumor microenvironment influence the biology of malignant cells in many hematologic malignancies, often through cytokine-mediated interactions. Recent studies involving healthy B cells and CD4+T cells identified an interplay between IL-6 and IL-21, whereby IL-6 increased IL-21 production by T cells, driving the differentiation and IL-6 secretion of nearby B cells. In addition to their known effects on healthy B cell function, IL-6 and IL-21 have also been implicated in the pathology of various lymphomas. In Waldenstrom's macroglobulinemia (WM), IL-6 is elevated in the bone marrow and is associated with increased IgM production. However, the function of IL-21 in the WM tumor microenvironment and its relationship to IL-6 is poorly understood. Our objective in this study was to characterize IL-21 production and function in WM and to examine the role of IL-6 and IL-21 in regulating interactions between malignant B cells and T cells in the tumor microenvironment. Immunohistochemistry revealed significant IL-21 staining in bone marrows of patients with WM (n=5), but the areas of infiltration by WM in the bone marrow sections appeared negative for IL-21 staining. To better understand the origin of IL-21 in in the tumor microenvironment, IL-21 expression was assessed by PCR in the CD19−CD138− fraction of cells remaining in patient bone marrow aspirates after positive selection for malignant B cells (n=5). IL-21 transcript was detected in 4/5 samples. CD19−CD138− cells activated with anti-CD3 and anti-CD28 antibodies expressed higher levels of IL-21 transcript and secreted significantly higher levels of IL-21 protein compared to unstimulated cells, suggesting that IL-21 in the WM bone marrow is derived from activated T cells. Intracellular expression of IL-21 protein was confirmed in CD4+ and CD8+ cells within the CD19−CD138− population using flow cytometry. Furthermore, dual staining of WM bone marrow sections with antibodies against IL-21 and CD3 or CD20 revealed co-staining of IL-21 with CD3+ T cells but not with CD20+ B cells. The response of WM B cells to T-cell derived IL-21 was then assessed in positively selected CD19+CD138+ WM B cells (n=5) and in the MWCL-1 cell line. Using flow cytometry, both the IL-21 receptor and the required common gamma chain subunit were detected on all patient samples as well as on MWCL-1 cells. Treatment of MWCL-1 cells with IL-21 (100 ng/mL) for 72 h increased proliferation by 35% (p<0.05) and IgM secretion by 80% (p<0.005). Similarly, in primary CD19+CD138+ WM cells (n=5), proliferation increased on average by 38% and IgM secretion by 71%. No apoptotic effects were associated with IL-21 in WM. Characterization of STAT activation in response to IL-21 revealed significant phosphorylation of STAT3 in both CD19+CD138+ WM cells and MWCL-1 cells and was associated with increases in BLIMP-1 and XBP-1 protein and decreases in PAX5. As STAT3 activation is known to regulate IL-6, we assessed the effect of IL-21 on B cell-mediated IL-6 secretion using ELISA. IL-21 significantly increased IL-6 secretion by both primary CD19+CD138+ WM cells (n=4) and MWCL-1 cells (87.9 +/− 10.9 ng/mL vs. 297.8 +/− 129.2 ng/mL, p<0.05). Treatment with IL-6 and IL-21 together had no additional effect over IL-21 alone on proliferation or IgM secretion in MWCL-1 cells, but culturing anti-CD3/anti-CD28-activated CD19−CD138−cells from WM bone marrows with IL-6 significantly increased IL-21 secretion (n=3). Overall, these data indicate that T-cell derived IL-21 significantly promotes growth and immunoglobulin production by malignant WM B cells and that subsequent IL-6 secretion by malignant B cells may enhance the secretion of IL-21 by T cells within the bone marrow microenvironment. 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.

Key Points STAT5 is constitutively phosphorylated in malignant B cells obtained from patients with Waldenström's macroglobulinemia. Inhibition of STAT5 signaling significantly decreases IgM production and may be useful therapeutically for patients with high IgM levels.

Abstract Purpose: Although the International Prognostic Score (IPS) is the gold standard for risk-stratifying patients with classical Hodgkin lymphoma (cHL), these criteria do not accurately predict outcome. As cytokines are critically involved in driving cHL, we tested whether pretreatment serum cytokine levels could provide additional prognostic information. Experimental Design: Thirty cytokines were measured in pretreatment serum from 140 patients with cHL and compared with 50 nonlymphoma controls. Patients were followed for event-free survival (EFS) and overall survival (OS), and Cox proportional hazards regression models were used to assess the association of individual cytokines and the cytokine profiles with outcome via unadjusted and IPS-adjusted HR. Results: Twelve cytokines (EGF, bFGF, G-CSF, HGF, IL-6, IL-8, IL-12, IL-2R, IP-10, MIG, TNF-α, and VEGF) were significantly (P &lt; 0.05) higher in patients with cHL than controls; elevated levels of HGF, IL-6, IL-2R, IP-10, and MIG were all associated with poorer EFS. Only interleukin-2 receptor (IL-2R; P = 0.002) and interleukin (IL)-6 (P &lt; 0.001) were independently prognostic. Patients with increased IL-6 and IL-2R had a significantly higher risk of early relapse and death, a finding that remained significant even after IPS-based risk stratification. Although elevated IL-6 and IL-2R correlated with the IPS, soluble CD30 (sCD30), and thymus and activation-related chemokine (TARC) levels, the two-cytokine model remained independently predictive of prognosis. Conclusions: Elevated pretreatment serum cytokines are associated with increased disease relapse and inferior survival in cHL. Thus, the pretreatment cytokine profile, particularly serum levels of IL-6 and IL-2R, may be used to identify patients with cHL at high risk for early-disease relapse. Clin Cancer Res; 19(24); 6812–9. ©2013 AACR.