Chesi, Marta

Abstract Abstract 1808 Poster Board I-834 We have developed the first mouse model of multiple myeloma (MM), Vk*MYC, in an immune competent mouse, with indolent plasma cell (PC) growth confined to the bone marrow, and in which the major biological and clinical features of the human disease are recapitulated, including the post germinal center origin of the tumor cells, the presence of a M-spike in the serum, anemia, diffuse bone disease and drug sensitivity. To further characterize karyotypically and phenotypically the Vk*MYC tumors, we performed gene expression profile (GEP) and aCGH analysis on CD138+ purified MM cells from Vk*MYC mice. For GEP, we analyzed 33 individual tumors on the Affymetrix 430_2 array for which publicly available datasets can be used to compare levels of gene expression. For aCGH, we used the Agilent 244K array to analyze 19 individual tumors. By GEP we first confirmed the PC origin of the Vk*MYC tumors, that clearly express the typical PC markers, including CD138, IRF4, BLIMP, XBP1, IgG or IgA, but not B cell markers like IgM, IgD, PAX5, or BCL6. Next, we analyzed the expression of the three cyclin D, that are almost universally dysregulated in human myeloma patients and cell lines, but are not expressed in normal human or murine PCs. We found that the Vk*MYC tumors express high levels of cyclin D2, and occasionally cyclin D1, but never cyclin D3 that, instead, is commonly expressed in B cells. Interestingly, in one sample lacking any D type cyclin expression we detected loss of Rb expression (and homozygous deletion of the gene, see below), as in the “TC none” group of human MM patients, highlighting once again the importance of this pathway in both human and mouse myeloma. aGCH analysis indicated that the genomic complexity of Vk*MYC tumors is low, and complex rearrangements were rarely observed. In contrast with the recurrent trisomy of odd number chromosomes present in approximately 50% of human MM patients, we found no evidences of hyperdiploidy in Vk*MYC mice, except perhaps in one tumor with trisomy 15 and 17. Instead, we detected monosomy 5 in 10/19, monosomy 14 in 4/19 and trisomy 16 in 4/19 tumors. Interestingly a large portion of the murine chr.14 is syntenic to the human chr.13, frequently lost in MM patients. After monosomy 13, the most frequent chromosomal change in human MM is loss of a sex chromosome. In the mouse, the most common numerical abnormality identified was loss of a sex chromosome: 10/11 male had loss of Y and 5/8 female had loss of X. From the analysis of aCGH data publicly available on the MMRC portal, we have generated a list of the most common bi-allelic deletions present in human myeloma patients and cell lines. Interestingly, several of these lesions are also present in Vk*MYC tumors. The Rb1 gene, frequently affected by monosomy 13 in human MM, is bi-allelically lost in 3/19 Vk*MYC tumors. In one case, we also detected a focal monoallelic deletion encompassing Rb1, in addition to the four tumors with monosomy 14. Other focal bi-allelic deletion identified are: Cdkn2a (p16 and p19ARF), FHIT and PTEN. The latter was found in a Vk*MYC tumor selected in-vivo to be bortezomib resistant. On chr.X we identified recurrent (5/19 tumors) bi-allelic deletions of UTX, the histone demethylase gene recently reported to be deleted in various cancers, including MM tumors and human myeloma cell lines. While we are in the process of performing functional studies in human cell lines to identify a role for UTX in myeloma pathogenesis, we took advantage of the relative genetic uniformity of the Vk*MYC mice to identify by GEP a signature associated with UTX lost. We separated our cohort of Vk*MYC tumors for which GEP data are available in two groups based on expression of UTX and generated by volcano plot a list of genes that distinguished the two groups. Strikingly, loss of UTX was associated with loss of expression of a subset of lymphoid genes and acquisition of a “macrophage signature”, suggesting a role for UTX in lineage commitment. These data provide a genetic basis for tumor plasticity similar to epithelial mesenchymal transition observed in some solid tumors, in which the tumor gradually acquires supporting characteristics of its microenvironment. We conclude that the Vk*MYC provide a remarkably faithful model of MM not only phenotypically but also genetically, that provides an excellent framework for functional characterization of the molecular pathogenesis of MM Disclosures Bergsagel: Genentech: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Merck: Research Funding.

High levels of circulating miR-16 in the serum of multiple myeloma (MM) patients are independently associated with longer survival. Although the tumor suppressor function of intracellular miR-16 in MM plasma cells (PCs) has been elucidated, its extracellular role in maintaining a nonsupportive cancer microenvironment has not been fully explored. Here, we show that miR-16 is abundantly released by MM cells through extracellular vesicles (EVs) and that differences in its intracellular expression as associated with chromosome 13 deletion (Del13) are correlated to extracellular miR-16 levels. We also demonstrate that EVs isolated from MM patients and from the conditioned media of MM-PCs carrying Del13 more strongly differentiate circulating monocytes to M2-tumor supportive macrophages (TAMs), compared with MM-PCs without this chromosomal aberration. Mechanistically, our data show that miR-16 directly targets the IKKα/β complex of the NF-κB canonical pathway, which is critical not only in supporting MM cell growth, but also in polarizing macrophages toward an M2 phenotype. By using a miR–15a-16-1–KO mouse model, we found that loss of the miR-16 cluster supports polarization to M2 macrophages. Finally, we demonstrate the therapeutic benefit of miR-16 overexpression in potentiating the anti-MM activity by a proteasome inhibitor in the presence of MM-resident bone marrow TAM.

Abstract Multiple myeloma (MM) is a predominantly incurable form of plasma cell cancer. Although immunomodulatory imide drugs (IMiDs) such as thalidomide, lenalidomide, and pomalidomide constitute the backbone of most MM therapies, little is understood about how these drugs function to alter the tumor/microenvironment in vivo. Recently, it was demonstrated that IMiDs bind to the substrate receptor protein cereblon (CRBN) leading to the ubiquitination and degradation of multiple neoantigen protein targets, often DNA-binding zinc finger regulatory proteins such as ZFP91, IKZF1 and IKZF3. Interestingly, CRBN differs in amino acid sequence between mice and humans rendering mice non-responsive to IMiDs’ effects. This difference has made it difficult to study the complex pleotropic actions of IMiDs in vivo. Consequently, our lab has generated an immunocompetent transgenic mouse that expresses full-length human CRBN under the control of its endogenous regulatory elements (hCRBN+). We crossed this mouse with our well-established Vk*MYC mouse to generate a novel humanized Vk*MYChCRBN+ strain that develops human-like multiple myeloma disease, is sensitive to IMiD therapy, and maintains a fully competent immune system. The purpose of generating our Vk*MYChCRBN+mouse is to determine the mechanism of action of IMiDs on the tumor only, the host only, and to understand the cross-talk between tumor and microenvironment in a clinically relevant in vivo model of MM. We find that hCRBN+ mice are sensitive to IMiD treatment in vivo by displaying degradation of known target proteins such as Ikzf1/Ikzf3 in splenocytes. We also show that non-tumor immune cells such as T and NK cells respond to IMiD treatment by increased proliferation and expression of effector molecules such as IL-2 and IFN-γ. Furthermore, by engrafting IMiD-sensitive Vk*MYChCRBN+ MM cells into an IMiD-insensitive WT host we establish that IMiDs have tumor-intrinsic effects in vivo that are independent of the host’s immune system. These tumor-intrinsic IMiD effects synergize not only with dexamethasone, which has been shown clinically, but also with enhancer-targeting BET or p300/CBP inhibitors. Conversely, when engrafting IMiD-insensitive Vk*MYC MM cells into an IMiD-sensitive hCRBN+ host we were unable to demonstrate significant IMiD-induced host immune activation or tumor suppression. We conclude, based on our preliminary data, that IMiD activity is predominantly tumor-intrinsic. Moving forward, we are currently utilizing single-cell RNA sequencing to map the cellular and transcriptional changes across time in both tumor cells and the immune microenvironment during IMiD treatment. Ultimately, our goal is to gain mechanistic understanding in order to optimize clinical practice. Citation Format: Seth J. Welsh, Meaghen E. Sharik, Victoria M. Garbitt, Link R. Taylor, Daniel L. Riggs, Caleb Stein, Grady Day, Courtney J. Hillukka, Zach J. Hammond, P Leif Bergsagel, Marta Chesi. A clinically relevant mouse model to understand how IMiDs modulate the host-tumor immunolandscape in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4628.

Abstract MYC dysregulation, the most common genetic aberration in multiple myeloma, is frequently due to the translocation of super-enhancers to the MYC locus. Several drugs target proteins that are enriched at many of these enhancers including BRD4 (BET inhibitors, BETi) and Ikaros (IMiDs), although their mechanism of action remains poorly understood. Here we present a characterization of the responses to these drugs in a collection of over sixty myeloma cell lines having a diversity of MYC rearrangements. We found that the anti-proliferative effects of these drugs significantly correlated with changes in MYC protein levels, consistent with both drugs targeting MYC expression. Despite this common target, there was no statistically significant correlation between the individual BETi and IMiD responses, suggesting that they act through different mechanisms. Of those lines having extremes of sensitivity or resistance, there were two major groups (BETiS/IMiDS and BETiS/IMiDR), a smaller group of four lines resistant to both drugs individually (BETiR/IMiDR) and only one line was BETiR/IMiDS. In the BETiR/IMiDR group, resistance to BETi was mediated by a BRD4-independent mechanism as BRD4 was efficiently released from the MYC-associated enhancers. In all three of BETiR/IMiDR cell lines that we examined, treatment with BETi and IMiD together abolished proliferation and down-regulated MYC, consistent with parallel BRD4- and Ikaros-dependent pathways driving MYC expression. These resistant lines all expressed high levels of the transcription factor ETV4 and knocking out its gene sensitized a line to each drug individually. Thus ETV4 appears to be necessary for the parallel pathways driving MYC expression. There were nine lines in the BETiS/IMiDR group. Sensitivity to BETi in these lines could be explained by either low ETV4 expression or by BETi repressing Ikaros levels (which was only observed in BETiS lines, suggesting that BRD4 drives IKZF1 expression in these lines). Thus, in ETV4-containing lines, BETi sensitivity is due to the simultaneously targeting of the BRD4- and Ikaros-dependent pathways. IMiD resistance likely was due to several reasons. In one cell line, OCIMY5, IMiD had little effect on Ikaros levels, likely due to the previously reported low levels of Cereblon. Seven of the eight remaining lines expressed high levels of either ETV4, or the other potential super-enhancer binding factors IRF4 or RUNX1. In the eight BETiS/IMiDS cell lines, IMiD strongly reduced both Ikaros and Aiolos protein levels, which likely caused IMiD sensitivity. As with the BETiS lines described above, the lines in this group either lacked ETV4 or BETi repressed Ikaros levels. In conclusion, by examining drug response in a collection of genetically annotated myeloma cell lines we have been able to identify factors that contribute the broad range of responses to BETi and IMiDs in myeloma cells. Citation Format: Daniel L. Riggs, Camille Herzog, Victoria M. Garbitt, Niamh Keane, Courtney J. Hillukka, Zachary J. Hammond, Julia E. Wiedmeier, Seth J. Welsh, Shulan Tian, Huihuang Yan, Ranjan Maity, Nizar Bahlis, Paola Neri, W Michael Kuehl, Marta Chesi, P Leif Bergsagel. IMiDs and BET inhibitors target distinct pathways of MYC dysregulation by super-enhancers in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3015.

Immunotherapy holds promise for patients with multiple myeloma (MM), but little is known about how MM-induced immunosuppression influences response to therapy. Here, we investigated the impact of disease progression on immunotherapy efficacy in the Vk*MYC mouse model. Treatment with agonistic anti-CD137 (4-1BB) mAbs efficiently protected mice when administered early but failed to contain MM growth when delayed more than 3 weeks after Vk*MYC tumor cell challenge. The quality of the CD8 + T cell response to CD137 stimulation was not altered by the presence of MM, but CD8 + T cell numbers were profoundly reduced at the time of treatment. Our data suggest that an insufficient ratio of CD8 + T cells to MM cells (CD8/MM ratio) accounts for the loss of anti-CD137 mAb efficacy. We established serum M-protein levels prior to therapy as a predictive factor of response. Moreover, we developed an in silico model to capture the dynamic interactions between CD8 + T cells and MM cells. Finally, we explored two methods to improve the CD8/MM ratio: anti-CD137 mAb immunotherapy combined with Treg depletion or administered after chemotherapy treatment with cyclophosphamide or melphalan efficiently reduced MM burden and prolonged survival. Together, our data indicate that consolidation treatment with anti-CD137 mAbs might prevent MM relapse.

Abstract The oncolytic reovirus (RV) has demonstrated clinical efficacy and minimal toxicity in a variety of cancers, including multiple myeloma (MM). MM is a malignancy of plasma cells that is considered treatable but incurable because of the 90% relapse rate that is primarily from drug resistance. The systemic nature of MM and the antitumor immunosuppression by its tumor microenvironment presents an ongoing therapeutic challenge. In the present study, we demonstrate that RV synergizes with the standard-of-care MM drug bortezomib (BTZ) and, importantly, enhances its therapeutic potential in therapy-resistant human MM cell lines in vitro. Using the syngeneic Vk*MYC BTZ-resistant immunocompetent transplantable MM murine model, we also demonstrate that mice harboring BTZ-insensitive MM tumors respond to the RV/BTZ combination treatment in terms of decreased tumor burden and improved overall survival (P < .00001). We demonstrate that BTZ augments RV replication in tumor-associated endothelial cells and myeloma cells, leading to enhanced viral delivery and thereby stimulating cytokine release, immune activity, apoptosis, and reduction of the MM-associated immune suppression. We conclude that combined RV/BTZ is an attractive therapeutic strategy with no safety signals for the treatment of MM.

Abstract Multiple myeloma (MM) is the second most common hematologic cancer, accounting for roughly 2% of all cancer deaths. Unfortunately, MM remains incurable and nearly all patients experience relapse. Recently, we have identified a novel cIAP1 antagonist, LCL161, with remarkable anti-MM effects. Interestingly, unlike in other tumor types, our previous work found that LCL161 does not directly induce apoptosis of MM cells, but rather drives activation and infiltration of macrophages to the tumor bed and phagocytosis of tumor cells. Furthermore, in vitro experiments demonstrate that the anti-MM activity of the agent relies on the presence of the tumor, with no observed increase in MM phagocytosis when macrophages are treated in isolation. However, LCL161 is a strong and indiscriminate transcriptional activator and thus, the molecular mechanisms underlying this immune response in MM remain poorly understood. In an effort to characterize molecular signatures associated with this response, we collected whole spleens from seven WT mice and eleven mice with VK12598 transplanted myeloma for single cell RNA-seq. Of the eleven tumor-bearing mice, three remained untreated, three were treated with LCL161, three with bortezomib, and three with cyclophosphamide. Additionally, one of the WT mice was treated with LCL161. Using the 10X genomics chromium platform, we measured mRNA levels in over 90,000 individual cells. We identified groups of cells with shared expression profiles, corresponding to known cell types, using graph-based clustering. Consistent with our previous work, we observed a marked reduction in tumor cells and activation of the noncanonical NFkB pathway in mice treated with LCL161. Turning our attention to cells identified as monocytes, with a particular focus on putative macrophages, we sought to identify molecular signatures associated with LCL161 treatment. Indeed, using a binomial model we identified over 500 upregulated genes in LCL161-treated macrophages. However, our previous data suggested that the efficacy of LCL161 was dependent on the presence of tumor cells. Thus, we refined these results by comparing the expression profile of macrophages treated with LCL161 in WT and tumor-bearing mice. These contrasts identified dozens of genes that were significantly upregulated in macrophages from LCL161 treated, tumor-bearing mice. Of note, we identified a small number of genes (including Spp1, Irg1, and Lipg) that were active only in macrophages from mice treated with LCL161 and bearing a transplanted tumor and unexpressed in all other cells. We believe these genes—and the pathways in which they are active—hold promise for the development of novel targeted therapies to better treat MM. Citation Format: Nicholas Banovich, Martin Boateng, Marta Chesi, Leif Bergsagel, Jonathan Keats. Single-cell RNA sequencing identifies macrophage-specific expression signatures associated with phagocytosis of multiple myeloma after treatment with cIAP antagonist [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3135.

Abstract Multiple myeloma (MM) is characterized by clonal expansion of malignant plasma cells (PCs) and aberrant production of monoclonal immunoglobulin detected as an M spike using serum protein electrophoresis. In the United States, MM represents ~15% of hematologic malignancies and is one of the few cancers increasing in incidence (e.g., 14,400 in 1996 to 30,330 in 2016, from SEER). Previously, a Vk*MYC mouse model was described, in which AID-dependent activation of MYC transgene in germinal center (GC) B cells catalyzes a highly penetrant, indolent MM after a prolonged latency. However, the indolent MM developed in Vk*MYC mice rarely progresses to a malignant stage, suggesting that additional genetic mutations are required for the malignant MM progression. Recent sequencing of paired tumor/normal samples from advanced or refractory MM patients identified that constitutive activation of Ras signaling pathway (KRAS: 23%; NRAS:20%; BRAF: 8%) associates with MM progression and therapy resistance. To determine whether oncogenic Nras promotes the progression of Myc-induced indolent MM to a malignant stage, we generated NrasLSL Q61R/+; Vk*MYC; IgG1-Cre (VQ) mice along with single mutant mice Vk*MYC; IgG1-Cre (Vk) or NrasLSL Q61R/+; IgG1-Cre (Q61R). To boost NrasQ61R expression in GC B cells, 6-7 weeks old mice were immunized with NP-CGG. A significant fraction of VQ mice developed M-spike after immunization and subsequently died of a highly malignant MM. The MM developed in some mice were restricted in bone marrow and spleen and thus mimicked majority of MM patients, while MM developed in other mice was primarily located in lymph nodes and represented patients with extramedullary MM. Both types of MM cells displayed hyperproliferation and hyperactivation of AKT and ERK pathways. They could be cultured for several weeks with their original stromal cells and in the presence of Il-6. The cultured MM cells could be easily infected or transfected. Upon transplantation, both types of MM cells caused a rapid lethality (within 16 and 4 weeks respectively) in secondary and tertiary recipients and preserved the initial locations of donor MM cells. MM recipient mice developed bone lesions and/or fractures characteristic of MM patients. Preliminary preclinical studies indicated that both types of MM cells were resistant to Bortezomib, a proteasome inhibitor commonly used in treating MM patients, and AZD6244, a potent MEK inhibitor. Additional tests of combinatorial therapies are ongoing. Taken together, we generated a novel mouse model in which activation of Vk*MYC and oncogenic Nras in GC B cells results in a highly malignant, transplantable MM. This model can serve as a platform to investigate pathogenesis of highly malignant multiple myeloma and test the efficacy of novel therapeutic agents. Citation Format: Zhi Wen, Adhithi Rajagopalan, Erik A. Ranheim, Remington Finn, Adam Pagenkopf, Grant Yun, Yun Zhou, Yidan Wang, Demin Wang, Marta Chesi, P. Leif Bergsagel, Fotis Asimakopoulos, Jing Zhang. Expression of oncogenic Nras and a MYC transgene in germinal center B cells induces a highly malignant multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3018.

Abstract Multiple myeloma (MM) is a tumor of terminally differentiated plasma cells that underwent affinity maturation and class switch recombination processes in germinal centers before homing to the bone marrow (BM), where they secrete large amounts of monoclonal immunoglobulins, clinically detected as an M-spike by serum protein electrophoresis (SPEP). Clinical manifestations of MM also include renal impairment, anemia, and bone disease, the latter resulting from abnormal osteoclast activation, which highlights the complex crosstalk between MM cells and their BM microenvironment. Chromosomal translocations into the immunoglobulin loci are the primary oncogenic events in ~50% of MM cases and are thought to occur as a result of errors during somatic hypermutation or class switch recombination. The other half of MM is characterized by trisomies of odd-numbered chromosomes. Both of these genomic abnormalities are present in the premalignant phase of MM called MGUS, which progresses to MM at a rate of 1% per year. Progression events include mutations of genes in the RAS/MAPK pathways; chromosomal rearrangements of the MYC locus; and mutations, amplifications, or biallelic deletions of genes in the NFkB pathway. Among the latter, the most common are deletions of TRAF3 or cIAP1 and -2 (BIRC2 and -3) and amplification or translocations of NIK (Map3k14), all resulting in NIK stabilization, phosphorylation of IKKα, processing of p100 to p52, NFKB2 nuclear translocation, and activation of the noncanonical NFKB pathway. This can be induced in MM cell lines in vitro by treatment with SMAC mimetics or IAP antagonists (IAPa), which induce cIAP1 auto-ubiquitination and degradation. We postulated that the resulting constitutive activation of the noncanonical NFKB pathway would render MM cells independent on the BM-localized survival signals provided by BAFF and APRIL, leading to extramedullary dissemination. We tested this hypothesis in vivo by exposing Vk*MYC mice with BM-localized MM to the IAP antagonist LCL161 and monitoring disease progression. In the immunocompetent Vk*MYC transgenic mouse model MYC expression is sporadically induced in germinal center cells by AID-dependent somatic hypermutation, leading to progressive accumulation of monoclonal plasma cells restricted to the BM that can be monitored over time by SPEP and M-spike quantization, as is done clinically in MM patients. Through a very rigorous testing of drugs whose clinical activity in MM has been assessed in clinical trials, we have also validated Vk*MYC mice as a faithful model to predict drug activity in MM, with a positive predictive value of 73% and a negative predictive value of 92%. To our surprise, treatment of Vk*MYC mice with the IAPa LCL161 did not promote MM extramedullary dissemination as we predicted, but rather induced a significant reduction in M-spike levels, indicative of reduction of tumor burden. Based on these preclinical data, we conducted a phase 2 clinical trial of LCL161 in combination with cyclophosphamide in relapsed/refractory MM patients. Results from 25 patients enrolled in the study demonstrated a response in five patients (1CR, 1 VGPR, 2PR, 1MR) and a median PFS of 10 months. Consistent with in vitro data on MM cell lines, LCL161 treatment did not promote direct apoptosis of Vk*MYC cells but phagocytosis of live cells, detectable by intravital microscopy within four hours after treatment. While LCL161 treatment of BM-derived macrophages (MΦ) in vitro promoted the acquisition of an inflammatory phenotype, with increased expression of IL6, IL12, and CD86 that resembled activation with CD40 agonists, it did not increase their phagocytic ability. In contrast, exposure of MΦ to LCL161 treated tumor cells or to the conditioned medium collected after LCL161 treatment enhanced phagocytosis. We therefore performed gene expression analysis on MM cells collected from Vk*MYC mice and MM patients before and after LCL161 treatment and identified marked upregulation of NFKB target genes, as expected, but also a type-I interferon (IFN) signature. Interestingly, the presence of blocking antibody to the IFN receptor subunit 1 (aIFNAR1) during LCL161 treatment of tumor cells inhibited their phagocytosis in vitro, and pretreatment of Vk*MYC mice with aIFNAR antibody abrogated LCL161 activity in vivo. Pretreatment of Vk*MYC mice with liposomal clodronate, known to deplete phagocytic cells, also abrogated LCL161 activity, indicating that MΦ-dependent phagocytosis, stimulated by the LCL161 induced tumor cell autonomous IFN response, is required for the anti-MM effects of LCL161. LCL161 has been shown to promote T-cell function in vitro, but in our hand LCL161 retained full anti-MM activity in T-cell deficient mice. However, while ~15% of immunocompetent mice were cured by just two weeks of LCL161 treatment, none of the T-cell deficient mice were, indicating a role for T cells in preventing disease recurrence. Consistently, rechallenge of cured mice with specific MM tumors induced expansion of IFNγ-producing T cells, indicative of reactivation of immunologic memory. We were surprised by the hyporesponsiveness of T cells to LCL161 in vivo and attributed it to the high levels of expression of the coinhibitory molecule PD1 we noted on both CD4 and CD8 cells irrespective of treatment. We also detected high levels of PDL1 on most CD11b+ myeloid cells as well as on a fraction of MM cells, which increased following LCL161 treatment. We therefore sought to combine LCL161 with an antibody against PD1. Remarkably, the combination of LCL161 with aPD1 was curative in all the mice that completed the two-week treatment, and we are in the process of translating this discovery to the clinic by opening a new trial of LCL161 in combination with aPD1. Citation Format: Marta Chesi, David Fooksman, Peter Leif Bergsagel. Immunomodulatory therapy of multiple myeloma with IAP antagonists [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr IA21.