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Dulos: Aduro Biotech Inc.: Equity Ownership. Lilian:Aduro Biotech Inc.: Equity Ownership. Snippert:Aduro Biotech Inc.: Equity Ownership. Guadagnoli:Aduro Biotech Inc.: Equity Ownership. Bertens:Aduro Biotech Inc.: Equity Ownership. David:Aduro Biotech Inc.: Equity Ownership. Anderson:Gilead: Membership on an entity's Board of Directors or advisory committees; Oncoprep: Equity Ownership; Oncoprep: Equity Ownership; Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acetylon: Equity Ownership; Acetylon: Equity Ownership; Millennuim: Membership on an entity's Board of Directors or advisory committees; Millennuim: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Equity Ownership; C4 Therapeutics: Equity Ownership; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Eenennaam:Aduro Biotech Inc.: Equity Ownership. Elsas:Aduro Biotech Inc.: Equity Ownership.

A PRoliferation Inducing Ligand (APRIL, TNFSF13), is a ligand for the receptors BCMA and TACI. APRIL serum levels are enhanced in patients diagnosed with Multiple Myeloma (MM), Chronic Lymphocytic Leukemia (CLL), and Colorectal Carcinoma correlated with poor prognosis. Our anti-APRIL antibody blocked CLL survival and inhibited mouse B1 hyperplasia in vivo (Guadagnoli et al., 2011). APRIL is produced by cells in the bone marrow niche, including myeloid-derived cells, osteoclasts and plasmacytoid dendritic cells. APRIL critically triggers BCMA in vitroand in vivoto drive proliferation and survival of human MM cells (Tai et al., 2016). Importantly, APRIL induces resistance to lenalidomide, bortezomib and other standard-of-care drugs. Furthermore, APRIL drives expression of PD-L1, IL-10, VEGF and TGFβ forcing an immunosuppressive phenotype on BCMA+ cells. As MM survival, resistance to treatment and the immunosuppressive phenotype can be blocked by neutralizing APRIL (Tai et al., 2016), development of an antibody blocking APRIL provides a novel avenue for the treatment of MM.

We have developed an assay to measure total cellular nuclease activity and compare activity levels across a spectrum of plasma cell dyscrasias. Total nuclease activity in cell lines and patient samples was assessed using a novel plasmid degradation assay. Briefly, multiple myeloma (MM) cell lines and primary MM patient cells were lysed at equal cell concentration. The lysates were mixed with plasmid DNA in triplicate/quadruplicate and incubated at 37°C for fixed time points ranging from 0 to 30 minutes. Following forced cessation of enzymatic activity, samples were fractionated on agarose gel and resultant image analyzed for band intensity by Kodak 1D Image analysis software. The ratio of degraded plasmid over time was analyzed via nonlinear regression to calculate a half-life and k-constant.Non-linear regression analysis of data derived from assays involving 6 MM cell lines (RPMI, OPM1, H292, U266, INA6 & MM1S) with three pellets each of equal size taken from non-confluent cell culture with > 85% viability showed statistically significant reproducibility of best fit curve with an average R-squared of 0.93. Similar regression analysis could not be performed on data derived from normal PBMC pellets because they showed minimal degradation with linear regression slope of (-0.62). Lastly, non-linear regression analysis on 22 patient samples with a plasma cell dyscrasia diagnosis, revealed a broader range of activity by half-life. Further differentiation of plasma cell dyscrasia patients into 2 groups revealed a significantly higher half-life in MGUS & smouldering (9499.8 minutes) versus newly diagnosed and refractory or relapsed multiple myeloma patients (9.4,19.3 minutes respectively).In conclusion, we show that nuclease activity, implicated in elevated recombination and genomic instability, can be measured in a statistically reproducible fashion by our in vitro assay and may be used to differentiate plasma cell dyscrasias across a clinical spectrum. Further analysis of nuclease activity in clinically annotated samples for correlation with clinical features, genomic data and survival outcomes is ongoing.Anderson: celgene: Consultancy; onyx: Consultancy; gilead: Consultancy; sanofi aventis: Consultancy; oncopep: Equity Ownership; acetylon: Equity Ownership.

Over the last decade, there has been increasing interest in mechanisms that underlie genomic instability which is implicated in tumor progression, development of drug resistance and possibly even oncogenesis. We have observed that dysregulated homologous recombination (HR) is an important contributor to genomic instability. In this study, we aim to broaden our understanding of HR by exploring alternate pathways that may affect genomic instability such as nuclease activity.

Munshi: Millennium Pharmaceuticals: Honoraria, Speakers Bureau. Anderson:Millennium Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Abstract 1569

Multiple myeloma (MM) is characterized by the accumulation of mature plasma cells in the bone marrow. Despite progress in treatment, the disease still remains incurable, therefore novel therapeutic approaches are required to achieve better treatment. Development of peptide-based immunotherapies against specific tumor-associated antigens offers an attractive approach that may lead to tumor-targeted cellular therapy in MM patients. CD138 (Syndecan-1) is an unique target expressed on the surface of MM cells and normal plasma cells with very limited other distribution or expression. CD138 has been reported to play an important role in myeloma cell survival and, infact, is used to purify MM cells in laboratory experiments. The purpose of this study was to develop immunogenic peptides derived from CD138 antigen for the induction of antigen-specific cytotoxic T lymphocytes (CTLs) against MM. We have identified an immunogeneic HLA-A2-specific CD138 peptide that is capable of inducing MM specific-CTLs. To induce the specific CTLs, HLA-A2-positive normal human T lymphocytes were stimulated with autologous dendritic cells or T2 cells pulsed with the CD138 peptide. The generated CTLs showed a distinct phenotype consisting of 67% of CD69+/CD45RO+ and 1% of CD45RA+/CCR7+ T cells, characteristic of effector memory cell population. A significant (p < 0.05) increase in T cell proliferation and IFN-g secretion were observed by the CTLs following restimulation with HLA-A2+/CD138+ MM cells. The CTLs displayed HLA-A2-restricted CD138-specific cytotoxic activity against MM cell, demonstrated as 76% and 86% cytotoxicity at Effector:Target ratios of 20:1 or 60:1, respectively. The MM cell-specific cytotoxicity was confirmed in “cold” target inhibition assays using HLA-A2.1+/CD138+ MM cells as “cold” inhibitor, demonstrated 25% and 39% reduction in cytotoxicity when incubated with cold inhibitors at E:T ratios of 20:1 or 60:1, respectively. A distinct CD138 peptide-specific tetramer+/CD8+ population was also confirmed. Taken together, these data demonstrate the efficacy of the immunogenic CD138 peptide in inducing a cellular immune response in MM for future clinical application.

X-box binding protein 1 (XBP-1) is a transcription factor is essential for the differentiation of plasma cells and the unfolded protein response. XBP-1 is significantly up-regulated in myeloma cells compared to both normal plasma cells and B-cells. Selective and specific requirement of XBP-1 for differentiation of B cells to plasma cells and its further up-regulation in multiple myeloma (MM) cells makes it a promising target for immunotherapy directed at MM. We have evaluated XBP-1 as a target antigen to develop MM-specific immunotherapy. In order to generate XBP-1 antigen-specific cytotoxic T lymphocytes (CTLs), we have identified HLA-A2-specific peptides derived from non-spliced (short form) and spliced (long form) XBP-1 proteins. We have further modified the peptide by altering one amino acid, which is critical for HLA-A2 affinity, to obtain epitope, which has higher stability to HLA-A2 clefts. The modified XBP-1 peptides were able to evoke higher levels of IFN-g release compared to native peptides and were able to induce CTLs highly specific to MM, demonstrated by Calcein-released cytotoxicity assay. Cytotoxic activity of these XBP1 peptide-specific-CTLs against U266, a HLA-A2+/XBP-1+ MM cell line was 60% and 79% by CTLs stimulated by non-spliced peptide and 69% and 88% by CTLs stimulated by spliced peptide at Effector:Target ratios of 20:1 and 60:1, respectively. The CTLs did not lyse HLA-A2− or XBP-1− cells. These results were further confirmed by the novel CD107 cytotoxicity assay, which detects MM-specific cytolytic CD8+ T cells by flow-cytometric analyses. The CTLs generated with XBP-1 peptide displayed distinct phenotypes, showing high CD69+CD45RO+ cell population (62% in non-spliced peptide-CTLs, 67% in spliced peptide-CTLs, 4% in unstimulated control-CTLs) and CD45RA+CCR7+ cell population (1% in non-spliced peptide-CTLs, 1% in spliced peptide-CTLs, 24% in unstimulated control-CTLs). In conclusion, we report the identification of highly immunogenic heteroclitic XBP-1 epitopes that have ability to generate MM-specific CTLs. Confirmation of in vivo activity of these CTLs in SCID mouse model is currently underway prior to its evaluation in clinical studies.

Hsp90 inhibitor has shown promising anti-tumor activity through the destabilization and eventual degradation of Hsp90 client proteins critical for cell survival. In this study, we examined the in vitro effects of Hsp90 inhibitor on the phenotype and function of human T lymphocytes and NK cells. We observed no significant effects of Hsp90 inhibitor treatment on cell survivals. However, Hsp90 inhibitor treatment for 24 hours led to irreversible down-regulation of expression of critical T-cell surface antigens including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab. Among the antigens evaluated, expression of CD4 antigen was most significantly downregulated (untrt vs. trt = 326 vs. 88 in Mean Fluorescence Intensity) following Hsp90 inhibitor treatment. Decreased CD3+ T lymphocytes proliferation (untrt vs. trt = 222839 cpm vs. 111102 cpm, 3[H]-thymidine incorporation) and reduced IFN-g secretion (untrt vs. trt = 77 vs. 48 pg/ml) was observed upon stimulation with allogeneic dendritic cells following 24 hrs treatments of T cells with Hsp90 inhibitor. Furthermore, CD3+ T-cell proliferation in response to mitogen stimulation, as measured by flow cytometry using CFSE was decreased following Hsp90 inhibitor treatment (untrt vs. trt = 41% vs. 3%, CFSE). Specifically, the CD4+CD28+ (untrt vs. trt = 32% vs. 1%) and CD8+CD28+ (untrt vs. trt = 27% vs. 17%) activated T-cell subpopulations displayed a significant decrease in proliferation in response to mitogen. Similarly, NK cells displayed decreased activation receptor expression including CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 and reduced cytotoxic activity against multiple myeloma cells (untrt vs. trt = 49% vs. 11% against MM1S cells, 65% vs. 8% against ARP cells) following Hsp90 inhibitor treatment. These studies demonstrate that Hsp90 inhibitor treatment significantly affects phenotype and function of human T-lymphocytes as well as NK cells, and suggest the need to monitor immune functions in patients being treated with Hsp90 inhibitor in our future studies.

Bortezomib is the first proteasome inhibitor approved for the therapy of multiple myeloma (MM) based on its in vitro and in vivo activity in myeloma. However, the toxicity and effects of this drug on the human immune function have not been entirely studied. In the present study, we evaluated the effects of Bortezomib on normal human immune cells including dendritic cells (DC), T lymphocytes and NK cells for cell survival, antigen expression, production of cytokines, and other key parameters of immune cell function. In our evaluation of effect of Bortezomib on DC, we did not observe significant change in the expression of cell surface antigens including CD40, CD80, CD83, CD86, HLA-ABC and HLA-DPQR molecules in terms of percentage of cells positive as well as mean fluorescence intensity (MFI). Bortezomib treated immature DC maintained the ability for antigen uptake as measured by uptake of Dextran-FITC (untrt vs. trt = 798 MFI vs. 802 MFI), maintained the expression levels of antigen uptake receptors including mannose (untrt vs. trt = 85% vs. 79%) and DEC-205 (untrt vs. trt = 49% vs. 42%), and the capacity to produce IL-12 (untrt vs. trt = 135 vs. 125 pg/ml). In addition, Bortezomib treated mature DC was able to induce comparable levels of allogenic T cell proliferation to the untreated mature DC as measured by 3[H]-Thymidine incorporation (untrt vs. trt = 212556 cpm vs. 220571 cpm). Furthermore, cell surface antigen expression including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab on T lymphocytes were not changed by Bortezomib treatment. The treated T cells also maintained the ability to secrete IFN-g secretion in response to allogenic DC (untrt vs. trt = 85 vs. 88 pg/ml) or Staphylococcal enterotoxin B (untrt vs. trt = 131 vs. 154 pg/ml). The cytolytic activity of the NK cell population was comparable between proteasome inhibitor treated and untreated control cells against the McCAR (untrt vs. trt = 44% vs. 52%) and MM1S (49% vs. 42%) target MM cell lines. This observation was correlated with similar expression levels of CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 activation antigens in treated versus untreated NK cells. These, in vitro results confirm lack of adverse effects of Bortezomib on immune function, and allow us to incorporate of Bortezomib in multimodality therapy that includes immunotherapy.

Hsp90, a molecular chaperone, plays a critical role in protein folding and transport, and thereby it modulates cellular activity. Pre-clinical data shows over-expression of Hsp90 in multiple myeloma (MM) and efficacy of Hsp90 inhibitor in myeloma has been determined in vitro. Based on these results, phase I/II trial evaluating clinical efficacy of the Hsp90 inhibitor is underway in MM. Although Hsp90 inhibitor shows significant effects on tumor cells, there is limited information concerning its effects on the immune system. The objective of this study was to evaluate the effects of Geldanamycin on activity of antigen-presenting cells. Immature and mature monocyte derived dendritic cells (DC) from normal human donors were used as the source of antigen-presenting cells in this study. Geldanamycin treatment of DC for 24 hours had no effect on cell viability (>90%), however, it led to a significant down-regulation of surface antigens associated with activation (CD86, CD80), maturation (CD83) and antigen presentation (HLA-ABC, HLA-DPQR). This decline was associated with changes in gene expression levels of these antigens, however the protein expression analyzed by % positive cells was not down-regulated with the treatment. Exposure to Hsp90 inhibitor was associated with significant decreases in IL-12 secretion (untrt vs. trt = 135 vs. 21 pg/ml), antigen uptake (MFI untrt 798 vs. MFI trt 449, Dextran-FITC), and antigen processing. These changes were associated with decline in DC function, which were demonstrated by significant decrease in Hsp90-treated DC compared to untreated DC in presentation of Tetanus Toxoid to autologous T lymphocytes (untrt vs. trt = 73 % vs. 47 %, CFSE proliferation), allogeneic T lymphocytes stimulation (untrt vs. trt = 232795 cpm vs. 116876 cpm, 3H-thymidine incorporation), and induction of IFN-g secretion from allogenic T lymphocytes (untrt vs. trt = 500 vs. 30 pg/ml). Taken together, these results show significant decline in DC function following Hsp90 inhibitor treatment. Further studies are underway using MM patient samples pre- and post-Hsp90 inhibitor treatment to understand in vivo effects on the immune system. Our pre-clinical data suggests the need to consider proper sequence of various therapeutic modalities, including immunotherapy, to optimize and improve clinical outcome.

Hsp90 inhibitor has shown promising anti-tumor activity through the destabilization and eventual degradation of Hsp90 client proteins critical for cell survival. In this study, we examined the in vitroeffects of Hsp90 inhibitor on the phenotype and function of human T lymphocytes and NK cells. We observed no significant effects of Hsp90 inhibitor treatment on cell survivals. However, Hsp90 inhibitor treatment for 24 hours led to irreversible down-regulation of expression of critical T-cell surface antigens including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab. Among the antigens evaluated, expression of CD4 antigen was most significantly downregulated (untrt vs. trt = 326 vs. 88 in Mean Fluorescence Intensity) following Hsp90 inhibitor treatment. Decreased CD3+T lymphocytes proliferation (untrt vs. trt = 222839 cpm vs. 111102 cpm, 3[H]-thymidine incorporation) and reduced IFN-g secretion (untrt vs. trt = 77 vs. 48 pg/ml) was observed upon stimulation with allogeneic dendritic cells following 24 hrs treatments of T cells with Hsp90 inhibitor. Furthermore, CD3+T-cell proliferation in response to mitogen stimulation, as measured by flow cytometry using CFSE was decreased following Hsp90 inhibitor treatment (untrt vs. trt = 41% vs. 3%, CFSE). Specifically, the CD4+CD28+(untrt vs. trt = 32% vs. 1%) and CD8+CD28+(untrt vs. trt = 27% vs. 17%) activated T-cell subpopulations displayed a significant decrease in proliferation in response to mitogen. Similarly, NK cells displayed decreased activation receptor expression including CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 and reduced cytotoxic activity against multiple myeloma cells (untrt vs. trt = 49% vs. 11% against MM1S cells, 65% vs. 8% against ARP cells) following Hsp90 inhibitor treatment. These studies demonstrate that Hsp90 inhibitor treatment significantly affects phenotype and function of human T-lymphocytes as well as NK cells, and suggest the need to monitor immune functions in patients being treated with Hsp90 inhibitor in our future studies.

Multiple myeloma (MM) is characterized by the accumulation of mature plasma cells in the bone marrow. Despite progress in treatment, the disease still remains incurable, therefore novel therapeutic approaches are required to achieve better treatment. Development of peptide-based immunotherapies against specific tumor-associated antigens offers an attractive approach that may lead to tumor-targeted cellular therapy in MM patients. CD138 (Syndecan-1) is an unique target expressed on the surface of MM cells and normal plasma cells with very limited other distribution or expression. CD138 has been reported to play an important role in myeloma cell survival and, infact, is used to purify MM cells in laboratory experiments. The purpose of this study was to develop immunogenic peptides derived from CD138 antigen for the induction of antigen-specific cytotoxic T lymphocytes (CTLs) against MM. We have identified an immunogeneic HLA-A2-specific CD138 peptide that is capable of inducing MM specific-CTLs. To induce the specific CTLs, HLA-A2-positive normal human T lymphocytes were stimulated with autologous dendritic cells or T2 cells pulsed with the CD138 peptide. The generated CTLs showed a distinct phenotype consisting of 67% of CD69+/CD45RO+and 1% of CD45RA+/CCR7+T cells, characteristic of effector memory cell population. A significant (p< 0.05) increase in T cell proliferation and IFN-g secretion were observed by the CTLs following restimulation with HLA-A2+/CD138+MM cells. The CTLs displayed HLA-A2-restricted CD138-specific cytotoxic activity against MM cell, demonstrated as 76% and 86% cytotoxicity at Effector:Target ratios of 20:1 or 60:1, respectively. The MM cell-specific cytotoxicity was confirmed in “cold” target inhibition assays using HLA-A2.1+/CD138+MM cells as “cold” inhibitor, demonstrated 25% and 39% reduction in cytotoxicity when incubated with cold inhibitors at E:T ratios of 20:1 or 60:1, respectively. A distinct CD138 peptide-specific tetramer+/CD8+population was also confirmed. Taken together, these data demonstrate the efficacy of the immunogenic CD138 peptide in inducing a cellular immune response in MM for future clinical application.

X-box binding protein 1 (XBP-1) is a transcription factor is essential for the differentiation of plasma cells and the unfolded protein response. XBP-1 is significantly up-regulated in myeloma cells compared to both normal plasma cells and B-cells. Selective and specific requirement of XBP-1 for differentiation of B cells to plasma cells and its further up-regulation in multiple myeloma (MM) cells makes it a promising target for immunotherapy directed at MM. We have evaluated XBP-1 as a target antigen to develop MM-specific immunotherapy. In order to generate XBP-1 antigen-specific cytotoxic T lymphocytes (CTLs), we have identified HLA-A2-specific peptides derived from non-spliced (short form) and spliced (long form) XBP-1 proteins. We have further modified the peptide by altering one amino acid, which is critical for HLA-A2 affinity, to obtain epitope, which has higher stability to HLA-A2 clefts. The modified XBP-1 peptides were able to evoke higher levels of IFN-g release compared to native peptides and were able to induce CTLs highly specific to MM, demonstrated by Calcein-released cytotoxicity assay. Cytotoxic activity of these XBP1 peptide-specific-CTLs against U266, a HLA-A2+/XBP-1+MM cell line was 60% and 79% by CTLs stimulated by non-spliced peptide and 69% and 88% by CTLs stimulated by spliced peptide at Effector:Target ratios of 20:1 and 60:1, respectively. The CTLs did not lyse HLA-A2−or XBP-1−cells. These results were further confirmed by the novel CD107 cytotoxicity assay, which detects MM-specific cytolytic CD8+T cells by flow-cytometric analyses. The CTLs generated with XBP-1 peptide displayed distinct phenotypes, showing high CD69+CD45RO+cell population (62% in non-spliced peptide-CTLs, 67% in spliced peptide-CTLs, 4% in unstimulated control-CTLs) and CD45RA+CCR7+cell population (1% in non-spliced peptide-CTLs, 1% in spliced peptide-CTLs, 24% in unstimulated control-CTLs). In conclusion, we report the identification of highly immunogenic heteroclitic XBP-1 epitopes that have ability to generate MM-specific CTLs. Confirmation of in vivoactivity of these CTLs in SCID mouse model is currently underway prior to its evaluation in clinical studies.

Bortezomib is the first proteasome inhibitor approved for the therapy of multiple myeloma (MM) based on its in vitroand in vivoactivity in myeloma. However, the toxicity and effects of this drug on the human immune function have not been entirely studied. In the present study, we evaluated the effects of Bortezomib on normal human immune cells including dendritic cells (DC), T lymphocytes and NK cells for cell survival, antigen expression, production of cytokines, and other key parameters of immune cell function. In our evaluation of effect of Bortezomib on DC, we did not observe significant change in the expression of cell surface antigens including CD40, CD80, CD83, CD86, HLA-ABC and HLA-DPQR molecules in terms of percentage of cells positive as well as mean fluorescence intensity (MFI). Bortezomib treated immature DC maintained the ability for antigen uptake as measured by uptake of Dextran-FITC (untrt vs. trt = 798 MFI vs. 802 MFI), maintained the expression levels of antigen uptake receptors including mannose (untrt vs. trt = 85% vs. 79%) and DEC-205 (untrt vs. trt = 49% vs. 42%), and the capacity to produce IL-12 (untrt vs. trt = 135 vs. 125 pg/ml). In addition, Bortezomib treated mature DC was able to induce comparable levels of allogenic T cell proliferation to the untreated mature DC as measured by 3[H]-Thymidine incorporation (untrt vs. trt = 212556 cpm vs. 220571 cpm). Furthermore, cell surface antigen expression including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab on T lymphocytes were not changed by Bortezomib treatment. The treated T cells also maintained the ability to secrete IFN-g secretion in response to allogenic DC (untrt vs. trt = 85 vs. 88 pg/ml) or Staphylococcal enterotoxin B(untrt vs. trt = 131 vs. 154 pg/ml). The cytolytic activity of the NK cell population was comparable between proteasome inhibitor treated and untreated control cells against the McCAR (untrt vs. trt = 44% vs. 52%) and MM1S (49% vs. 42%) target MM cell lines. This observation was correlated with similar expression levels of CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 activation antigens in treated versus untreated NK cells. These, in vitroresults confirm lack of adverse effects of Bortezomib on immune function, and allow us to incorporate of Bortezomib in multimodality therapy that includes immunotherapy.

Hsp90, a molecular chaperone, plays a critical role in protein folding and transport, and thereby it modulates cellular activity. Pre-clinical data shows over-expression of Hsp90 in multiple myeloma (MM) and efficacy of Hsp90 inhibitor in myeloma has been determined in vitro. Based on these results, phase I/II trial evaluating clinical efficacy of the Hsp90 inhibitor is underway in MM. Although Hsp90 inhibitor shows significant effects on tumor cells, there is limited information concerning its effects on the immune system. The objective of this study was to evaluate the effects of Geldanamycin on activity of antigen-presenting cells. Immature and mature monocyte derived dendritic cells (DC) from normal human donors were used as the source of antigen-presenting cells in this study. Geldanamycin treatment of DC for 24 hours had no effect on cell viability (>90%), however, it led to a significant down-regulation of surface antigens associated with activation (CD86, CD80), maturation (CD83) and antigen presentation (HLA-ABC, HLA-DPQR). This decline was associated with changes in gene expression levels of these antigens, however the protein expression analyzed by % positive cells was not down-regulated with the treatment. Exposure to Hsp90 inhibitor was associated with significant decreases in IL-12 secretion (untrt vs. trt = 135 vs. 21 pg/ml), antigen uptake (MFI untrt 798 vs. MFI trt 449, Dextran-FITC), and antigen processing. These changes were associated with decline in DC function, which were demonstrated by significant decrease in Hsp90-treated DC compared to untreated DC in presentation of Tetanus Toxoid to autologous T lymphocytes (untrt vs. trt = 73 % vs. 47 %, CFSE proliferation), allogeneic T lymphocytes stimulation (untrt vs. trt = 232795 cpm vs. 116876 cpm, 3H-thymidine incorporation), and induction of IFN-g secretion from allogenic T lymphocytes (untrt vs. trt = 500 vs. 30 pg/ml). Taken together, these results show significant decline in DC function following Hsp90 inhibitor treatment. Further studies are underway using MM patient samples pre- and post-Hsp90 inhibitor treatment to understand in vivoeffects on the immune system. Our pre-clinical data suggests the need to consider proper sequence of various therapeutic modalities, including immunotherapy, to optimize and improve clinical outcome.