Abstract 1887: Anti-CD38/CD28xCD3 trispecific T cell engager induces proliferation of primary T cells and mediates potent killing of primary malignant plasma cells isolated from Multiple Myeloma bone marrow aspirates
Dominant Expression of PVRIG and TIGIT Inhibitory Pathways in Bone Marrow of Multiple Myeloma Patients
Abstract Introduction Blocking inhibitory immune checkpoints holds promise to treat multiple myeloma (MM) patients. However, currently available checkpoint inhibitors have not shown significant clinical benefits for MM patients, warranting the need for alternative checkpoint blockers. The immune checkpoint TIGIT was recently shown to be the most upregulated immune inhibitory receptor on CD8+ T cells in MM patients' bone marrow (BM), compared to other checkpoints (Guillerey C., Blood. 2018). Preclinical models demonstrated the dominant effects of TIGIT blockade or depletion, by significantly improving mice survival, reducing myeloma cell numbers and exhausted T cell hallmarks (Minnie S., Blood. 2018). As a result, several clinical trials using anti-TIGIT monoclonal antibodies have been recently initiated in MM patients. The DNAM-1 family, in addition to TIGIT, also includes the inhibitory receptor PVRIG, that competes with the co-activating receptor DNAM-1 for the binding to the shared ligand PVRL2, similarly to the TIGIT/PVR/DNAM-1 interaction. Accordingly, TIGIT and PVRIG co-blockade were shown to synergize in enhancing T cell activity and anti-tumor activity in preclinical models (Whelan S., Cancer Immunol. Res. 2019). PVRL2 together with PVR (ligand of TIGIT) were shown to be highly expressed on plasma cells and on CD14+ cells in BM of MM patients (Lozano E., Clin. Cancer Res. 2020). This study aimed at evaluating DNAM-1 axis receptors expression in MM patients' BM. Methods Fresh BM aspirates were collected from 21 MM patients with progressive disease (PD) or in complete response (CR) after obtaining IRB approval. BM mononuclear cells were isolated and single cell suspensions were obtained followed by staining with anti-human antibodies to evaluate DNAM-1 axis members and PD-1 expression. BM biopsies from 6 MM patients (each patient had 4 core on the Tissue Micro-Array T291 USBiomax) were stained for PVRL2 expression by immuno-histochemistry (IHC). Results Flow cytometry analysis of PD-1 and DNAM-1 axis receptors revealed a significant lower fraction of PD1+ cells among cell populations examined compared with other receptors. TIGIT expression was the highest on NK, CD8+ and NKT cells compared to CD4+ T cells, which is in line with previous published data (Lozano E. Clin. Cancer Res. 2020). In contrast, DNAM-1 was expressed on CD8+ T, NK and NKT cells with prominent high expression on CD4+ T cells (Fig 1A). The highest expression among the receptors was of PVRIG on all lymphoid populations, except CD4+ where DNAM-1 was more highly expressed. Importantly, 50% of CD8+ T cells co-expressed TIGIT and PVRIG, supporting a combinatorial therapeutic approach (Fig. 1B). Additionally, the expression of the PVRL2 ligand on MM plasma and endothelial cells was demonstrated by IHC. FACS analysis further supported PVRL2 expression on plasma cells in MM BM (Fig 2). A higher expression of PVRIG, TIGIT and PD-1 was present on DNAM-1 negative CD8+ T cells (Fig 3A, B), suggesting accumulation of exhausted cells in MM tumor microenvironment (TME) as previously described (Minnie S., Blood. 2018). PVRIG had significantly higher expression on DNAM+ cells, compared to PD-1 and TIGIT (Fig 3C), suggesting the potential of its blockade to enhance DNAM-1 activation and subsequent proliferation of earlier differentiated memory cells in MM TME. Finally, CR patients had a trend for higher DNAM-1 expression on CD8+ T cells compared to those with PD (Fig 3D). This is consistent with other reports in mice showing that the expression of DNAM-1 negatively correlates with BM myeloma cell numbers (Minnie S., Blood. 2018). Conclusions DNAM-1 axis receptors are dominantly expressed on lymphocytes in BM of MM patients, with PVRIG exhibiting the most prominent expression. The reduced expression of DNAM-1 in PD patients' TME, compared to CR patients, suggests a link between DNAM-1 axis and clinical outcomes. Recent data suggest TIGIT is an attractive target for blockade in MM. Our new findings highlight for the first time the dominant expression of PVRIG, as well as TIGIT, and suggest that combined blockade of TIGIT with PVRIG may potentially benefit MM patients, placing the DNAM-1 axis as a dominant pathway in MM therapy. Figure 1 Figure 1. Disclosures Frenkel: Compugen Ltd.: Current Employment, Other: in the event of frontal participation, I will be reimbursed for my travel expenses by Compugen Ltd.. Alteber: Compugen Ltd.: Current Employment. Cojocaru: Compugen Ltd.: Current Employment. Ophir: Compugen Ltd.: Current Employment.
Abstract Abstract 1908 Introduction: Tumor vaccines hold promise as a means of eliciting anti-myeloma immunity and controlling disease that may be resistant to chemotherapy and biologic therapy. We have developed a whole cell tumor vaccine, whereby patient derived plasma cells are transduced with an attenuated vaccinia vector that contains transgenes for the costimulatory molecules B7.1 (CD80), ICAM-1 (CD54), and LFA-3 (CD58), designated TRIad of COstimulatory Molecules (TRICOM). In this manner, a broad array of tumor antigens, including those which may be specific to a given patient, are presented in the context of costimulatory molecules that have been shown to be synergistic in the stimulation of the effector T-cells. In the present study, we evaluated the phenotype and functional characteristics of TRICOM transduced primary myeloma cells. Methods and results: Plasma cells were isolated from bone marrow aspirates obtained from patients with multiple myeloma following Ficoll density centrifugation. Bone marrow derived mononuclear cells were infected with a replication-defective poxviral vector, the modified vaccinia Ankara strain (MVA), encoding TRICOM, or a control empty MVA vector. The expression of costimulatory molecules was assessed using flow cytometric analysis 3 hrs following viral infection. Viral transduction using the TRICOM vector at the dose of 20 MOI (multiplicity of infection) increased the mean percentage of CD38+ cells expressing CD80, CD54 and CD58 from a minimal baseline level (below 5%) to 70%, 56% and 47%, respectively (n=4). Transduction with control MVA vector did not augment expression of costimulatory molecules on plasma cells (mean percent expression of CD80, CD54 and CD58 of 2.6%, 2.7% and 3.8%, respectively, n=4). Of note, compared to CD38+ plasma cells, the CD38 negative fraction of bone marrow derived mononuclear cells demonstrated a significantly lower TRICOM transduction efficiency (mean percent expression of CD80, CD54 and CD58 of 16%, 17% and 16%, respectively, n=4, p<0.05 compared to CD38+ plasma cells). The ability of MVA-TRICOM transduced plasma cells to stimulate autologous T cell populations in vitro was assessed. Patient derived T-cells were purified from the non-adherent portion of PBMC by magnetic bead separation. MVA-TRICOM or empty MVA vector infected plasma cells were irradiated with 20Gy and co-cultured with autologous T cells at a 10:1 ratio of effector cells to vaccine for 7 days. MVA-TRICOM transduced plasma cells potently stimulated activated T cell responses, as assessed by the percentage of CD4+/CD25+/CD69+ T-cells (mean 7.8% of activated T-cells with TRICOM vaccine vs. 2.7% with control vaccine, n=3, p<0.05). In contrast, vaccine stimulation did not result in regulatory T-cell expansion, assessed as the percentage of cells co-expressing CD4,CD25 and FoxP3 (2.4% vs. 2.3%, for TRICOM and control vaccine, respectively, n=3). In concert with these findings, vaccine stimulation resulted in a polarization towards Th1 cytokine secretion, with 7.9% of CD4+ T-cells expressing intracellular IFN-γ after stimulation with TRICOM vaccine as compared to 5.4% after stimulation with the control vaccine (n=3, p<0.05). To further assess the expansion of tumor specific T cell populations, the ability of vaccine stimulated T cells to kill autologous tumor was assessed in a cell-based fluorogenic cytotoxicity assay. MVA-TRICOM transduced plasma cells potently stimulate the expansion of myeloma specific CTLs with the capacity to lyse autologous tumor targets. Mean CTL lysis was 20% and 8% for vaccine stimulated and unstimulated T cells respectively (n=2). Conclusions: Malignant plasma cells transduced with MVA-TRICOM strongly express costimulatory molecules, and potently stimulate activated, tumor reactive T cell populations. This preclinical data serves as a platform for developing a phase 1 clinical trial evaluating the use of MVA-TRICOM transduced autologous plasma cells in patients with multiple myeloma. Disclosures: No relevant conflicts of interest to declare.
Abstract Introduction:TIGIT (T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif [ITIM] domain) is an inhibitory immunoreceptor expressed by T and natural killer (NK) cells that is an important regulator of anti-tumor and anti-viral immunity. TIGIT shares its high-affinity ligand PVR (CD155) with the activating receptor CD226 (DNAM-1). We have recently shown that TIGIT blockade, together with PD-L1/PD-1 blockade, provides robust efficacy in syngeneic tumor and chronic viral infection models. Importantly, CD226 blockade abrogates the benefit of TIGIT blockade, suggesting additional benefit of TIGIT blockade through elaboration of CD226-mediated anti-tumor immunity, analogous to CTLA-4/CD28 regulation of T-cell immunity. Whether TIGIT and CD226 are expressed in patients with multiple myeloma (MM) and how TIGIT expression relates to PD-L1/PD-1 expression is unknown. Here we evaluate expression of TIGIT, CD226, PD-1 and PD-L1 in patients with MM to inform novel immunotherapy combinations. Methods:We performed multi-color flow cytometry (n = 25 patients), and multiplex qRT-PCR (n = 7) on bone marrow specimens from patients with MM to assess expression of TIGIT, CD226, PD-1, and PD-L1 on tumor and immune cells. Cells were stained with fluorescently conjugated monoclonal antibodies to label T cells (CD3, CD4, CD8), NK cells (CD56, CD3), plasma cells (CD38, CD45, CD319, CD56), inhibitory/activating receptors (PD-1, TIGIT, PD-L1, CD226), and an amine-reactive viability dye (7-AAD). Stained and fixed cells were analyzed by flow cytometry using BD FACSCanto™ and BD LSRFortessa™. Results:TIGIT, CD226 and PD-L1/PD-1 were detectable by flow cytometry in all patients with MM who were tested, with some overlapping and distinct expression patterns. TIGIT was commonly expressed by marrow-infiltrating CD8+ T cells (median, 65% of cells), CD4+ T cells (median, 12%) and NK cells. In contrast, CD226 was more commonly expressed by marrow-infiltrating CD4+ T cells (median, 74%) compared with CD8+ T cells (median, 38%). PD-1 was expressed by marrow-infiltrating CD8+ T cells (median 38%) and CD4+ T cells (median, 16%). TIGIT was co-expressed with PD-1 on CD8+ T cells (67%-97% TIGIT+ among PD-1+), although many PD-1-negative CD8+ T cells also expressed TIGIT (39%-78% of PD-1-negative). PD-L1 was also expressed by CD8+ (median, 23%) and CD4+ (median, 8%) T cells in addition to MM plasma cells (median, 95%), albeit with significantly lower intensity on T cells compared with plasma cells. The expression of TIGIT and PD-L1 mRNA was highly correlated (R2 = 0.80). Analysis of PVR expression will also be presented. Conclusions: TIGIT, CD226, PD-1, and PD-L1 were commonly expressed in MM bone marrow, but with different patterns. Among CD8+ T cells, the frequency of TIGIT+ T cells was almost twice that of PD-1+ T cells, whereas the majority of CD4+ T cells expressed CD226. TIGIT blockade may complement anti-PD-L1/PD-1 immunotherapy by activating distinct T-cell/NK-cell subsets with synergistic clinical benefit. These results provide new insight into the immune microenvironment of MM and rationale for targeting both the PD-L1/PD-1 interaction and TIGIT in MM. Disclosures Yadav: Genentech, Inc.: Employment. Green:Genentech, Inc.: Employment. Ma:Genentech, Inc.: Employment. Robert:Genentech, Inc.: Employment. Glibicky:Makro Technologies Inc.: Employment; Genentech, Inc.: Consultancy. Nakamura:Genentech, Inc.: Employment. Sumiyoshi:Genentech, Inc.: Employment. Meng:Genentech, Inc.: Employment, Equity Ownership. Chu:Genentech Inc.: Employment. Wu:Genentech: Employment. Byon:Genentech, Inc.: Employment. Woodard:Genentech, Inc.: Employment. Adamkewicz:Genentech, Inc.: Employment. Grogan:Genentech, Inc.: Employment. Venstrom:Roche-Genentech: Employment.
Programmed cell death (PD)-1/PD-Ligand 1(PD-L1) blockade that reinvigorates exhausted T cells has been approved for the treatment of various solid tumors and hematological malignancies. However, in a clinical trial of multiple myeloma (MM) patients, anti-PD-1 monotherapy did not result in a clinical response. Furthermore, clinical trials of combining PD-1 blockade with immunomodulatory drugs or anti-CD38 monoclonal antibody failed to demonstrate clinical benefits in MM patients. To overcome the limitation of anti-PD-1 therapy in MM, the phenotype and differentiation of CD8+ T cells need to be characterized in the bone marrow (BM) of MM patients, particularly by analyzing myeloma antigen-specific CD8+ T cells. In addition, the role of immunosuppressive factors abundant in the MM microenvironment should be considered, including TGF-β. First, we confirmed the upregulation of PD-1 and PD-L1 expression in CD8+ T cells and myeloma cells, respectively, from the BM of MM patients. PD-1-expressing CD8+ T cells from the BM of MM patients co-expressed other checkpoint inhibitory receptors including Tim-3, LAG-3, and TIGIT. We also investigated the expression of T-cell transcription factors, such as T-bet, and EOMES, which are related to T-cell differentiation. In BM from MM patients, PD-1+CD8+ T cells had a higher percentage of EomeshiT-betlo cells than PD-1-CD8+ T cells. These data demonstrate that PD-1-expressing CD8+ T cells from the BM of MM patients exhibit a terminally differentiated phenotype with co-expression of multiple immune checkpoint inhibitory receptors. These results were also observed in BM CD8+ T cells specific to myeloma antigens NY-ESO-1 and HM1.24. Next, we investigated proliferation and cytokine production of BM CD8+ T cells from MM patients. BM CD8+ T cells from MM patients exhibited reduced proliferation and cytokine production upon T cell receptor (TCR) stimulation, compared to BM CD8+ T cells from other control group such as of undetermined significance. However, both anti-PD-1 alone and combined blockade of PD-1 with other immune checkpoint receptors, such as Tim-3, Lag-3, or TIGIT, did not increase the proliferation of BM CD8+ T cells from MM patients. Likewise, anti-PD-1 treatment failed to induce reinvigoration of BM CD8+ T cells stimulated with HLA-A*0201-restricted myeloma antigen peptides, including NY-ESO-1157-165 and HM1.2422-30 peptides. These data demonstrate that blocking PD-1 is not sufficient to restore the function of BM CD8+ T cells from MM patients. It has been known that TGF-β, which is actively secreted by malignant plasma cells and BM stromal cells, can inhibit T-cell responses. We confirmed that the major source of TGF- β1 is plasma cells including myeloma cells among BMMCs from MM patients, and the number of TGF- β1-producing plasma cells, including myeloma cells, is increased in the BM of MM patients. We investigated whether blocking TGF-β signaling enhances reinvigoration of BM CD8+ T cells from MM patients. The combined blockade of PD-1 and TGF- β significantly increased the proliferation of BM CD8+ T cells from MM patients in the presence of TCR stimulation. The production of IFN-γ and TNF by BM CD8+ T cells was also rescued by combined blockade of PD-1 and TGF-β. Moreover, combination of anti-PD-1 antibody and TGF-β inhibitors increased proliferative responses of BM CD8+ T cells from HLA-A2+ MM patients stimulated with a mixture of HLA-A*0201-restricted myeloma antigen peptides (NY-ESO-1157-165 and HM1.2422-30 peptides). Thus, PD-1 blockade reinvigorates BM CD8+ T cells from MM patients in the presence of TGF-β inhibitors. Taken together, BM CD8+ T cells and myeloma antigen-specific CD8+ T cells express increased levels of PD-1 and have a terminally exhausted phenotype in MM patients. Under TGF-β inhibition, anti-PD-1 reinvigorates BM CD8+ T cells from MM patients, but PD-1 blockade alone does not restore the function of BM CD8+ T cells. Blocking both TGF-β and PD-1 can be a promising therapeutic strategy for the treatment of MM. Disclosures No relevant conflicts of interest to declare.
Abstract Introduction B-cell maturation antigen (BCMA) is a cell surface receptor highly and selectively expressed on normal plasma cells and transformed plasma cells in multiple myeloma (MM) patients. Upon ligand binding, BCMA initiates signals that promote the survival of MM cells and the production of immunosuppressive factors. Therapeutics that target BCMA are being investigated in the clinic, with encouraging preliminary results. HPN217 is a Tri-specific T Cell-Activating Construct (TriTAC) specific to BCMA, to serum albumin for half-life extension, and to CD3ε for redirecting T cells against MM cells. It is currently being evaluated in a phase 1 /2 clinical trial for relapsed or refractory MM (NCT04184050). Herein, we describe translational studies to examine factors that may impact the therapeutic efficacy of HPN217, including the target BCMA, in membrane-bound or soluble form, and concomitant or combination therapeutics such as γ-secretase inhibitor (GSI) and dexamethasone. Results To evaluate the effects of HPN217 against primary MM cells, we used a patient-derived 3D-culture system (3DTEBM) designed to recapitulate the biology within the bone marrow microenvironment. 3DTEBM seeded with bone marrow accessory cells and autologous plasma recreate niches along an oxygen gradient that enable the survival and expansion of autologous MM cells without additional nutrient supplements. 3DTEBM's were established from 5 MM patients with varying ratios of autologous CD3+ T cells to MM cells (0.15-0.6). Although the functional competence of the T cells was unknown, HPN217 was able to mediate MM cell killing in 80% of the cultures with up to 71% of MM cells eliminated at a T cell/MM cell ratio of 0.45. The anti-tumor efficacy of HPN217 correlated strongly (R 2 = 0.99) with BCMA expression on the MM cells as measured by flow cytometry, suggesting the number of target receptors can be a limiting factor in efficacy. Consistent with this result, pre-incubation of target cells with 1 or 10 μg/mL anti-BCMA reduced the activity of HPN217 in T cell-dependent cellular cytotoxicity (TDCC) assays using healthy donor T cells and MM cell lines. Soluble BCMA (sBCMA) is produced when the extracellular domain of BCMA is cleaved by γ-secretase. It may act as a sink for HPN217. There was no correlation between the activity of HPN217 and the quantity of sBCMA in 3DTEBM. However, in TDCC assays, the addition of 6.25, 25 and 100 nM recombinant BCMA respectively led to 4-, 9- and 28-fold increases in the EC 50 of HPN217. Taken together, these data underscore the importance of preserving BCMA on MM cells and reducing sBCMA in circulation. Interestingly, treatment of MM cell line RPMI8226 with the GSI LY-3039478 for 24 hours increased the cell surface expression of BCMA by 3.6 folds. Using RPMI8226 as target cells in the 3DTEBM system, LY-3039478 increased the killing efficacy of HPN217-redirected primary T cells by 1.9 folds. Dexamethasone (Dex) is used with other therapeutics for treating MM. It is also commonly given to manage cytokine release syndrome (CRS) caused by T cell engagers. We conducted TDCC assays in the presence of 0.07-300 nM Dex to simulate plasma concentrations relevant to dose levels of Dex premedication for CRS. The highest Dex concentrations caused ≤3-fold increases in the EC 50 of HPN217. Considering this and the plasma half-life of i.v. injected Dex at <5 h, the suppressive effect of Dex on the anti-tumor activity of HPN217-redirected T cells may be limited. We then evaluated if MM.1S-Luc cell line xenografts in NCG mice would be a suitable model to extend the above in vitro findings to an in vivo setting. Lesions in the spine, skull and femur in NCG mice treated with vehicle could be detected by bioluminescent imaging. All mice succumbed to the disease within 40 days. By contrast, animals treated with HPN217 were protected in a dose-dependent manner. Mice that received the highest dose remained 100% disease-free at the end of the study (Figure 1). Conclusions We demonstrated HPN217 mediated BCMA-dependent primary MM cell killing by autologous T cells, and that the density of BCMA target on the surface of MM cells and sBCMA affected the efficacy of HPN217 in cultures. GSI, which increased the expression of BCMA on MM cells, enhanced the efficacy of HPN217. On the other hand, Dex had limited negative effect. HPN217 in combination with approved and experimental MM therapeutics is being evaluated in the 3DTEBM and MM.1S-Luc models. Figure 1 Figure 1. Disclosures Ng: Harpoon Therapeutics: Current Employment, Current equity holder in publicly-traded company. Aaron: Harpoon Therapeutics: Current Employment, Current equity holder in publicly-traded company. Callihan: Harpoon Therapeutics: Current Employment, Current equity holder in publicly-traded company. Hemmati: Harpoon Therapeutics: Current Employment, Current equity holder in publicly-traded company. Law: Harpoon Therapeutics: Current Employment, Current equity holder in publicly-traded company. Azab: Cellatrix, LLC: Current Employment, Current holder of individual stocks in a privately-held company. Sun: Harpoon Therapeutics: Consultancy, Current equity holder in publicly-traded company, Ended employment in the past 24 months.
Abstract The expression of Cancer Germline Antigens (CGAgs) is normally restricted to the pre-meiotic spermatogonia cells of the testis. The testis is an immunologically privileged site and so immunological tolerance to CGAg is not established. However, CGAg expression is also detected in many types of malignant disease including plasma cells from patients with multiple myeloma. CGAg expression has been shown to prime a T cell immune response in many patients with solid tumours and this may offer a novel target for immunotherapy in patients with myeloma. We have used immunodominant peptide epitopes from a range of CGAgs to screen for CGAg-specific T cells in the blood of patients with multiple myeloma at various stages of their disease. Initial studies demonstrated that T cells from 15 out of 37 patients responded to one or more CGAg peptides and the magnitude of the CGAg-specific CD8+ T cell response ranged between 0.0004% and 0.1% of the total CD8+ T cell pool. Serial analysis showed that these immune responses were detectable in individual patients at multiple time-points during the course of their disease. A further 13 peptides have now been obtained including several CD4 peptide. We have subsequently cloned CD4 T cells specific to a MAGE 3 peptide and have shown them to be functional. In some patients we determined the membrane phenotype of the CGAg-reactive cells as CD45RA+ and CCR7−, an effector memory differentiation state. CGAg-specific responses have also been detected in patients with clinically benign forms of paraproteinaemia indicating that T cell immunity may play a role in the control of disease progression. Plasma cells are localised to bone marrow and we are now focussing on the study of immunity to CGAg at this site. Initial findings indicate a higher proportion of CGAg-specific T cells within bone marrow and the phenotypic profile of these cells is being determined. Functional T cells specific for CGAg are therefore present in a large proportion of patients with multiple myeloma and offer the possibility of a novel approach for immunotherapy in this disease.
AbstractMultiple myeloma remains a largely incurable disease of clonally expanding malignant plasma cells. The bone marrow microenvironment harbors treatment-resistant myeloma cells, which eventually lead to disease relapse in patients. In the bone marrow, CD4+FoxP3+ regulatory T cells (Tregs) are highly abundant amongst CD4+ T cells providing an immune protective niche for different long-living cell populations, e.g., hematopoietic stem cells. Here, we addressed the functional role of Tregs in multiple myeloma dissemination to bone marrow compartments and disease progression. To investigate the immune regulation of multiple myeloma, we utilized syngeneic immunocompetent murine multiple myeloma models in two different genetic backgrounds. Analyzing the spatial immune architecture of multiple myeloma revealed that the bone marrow Tregs accumulated in the vicinity of malignant plasma cells and displayed an activated phenotype. In vivo Treg depletion prevented multiple myeloma dissemination in both models. Importantly, short-term in vivo depletion of Tregs in mice with established multiple myeloma evoked a potent CD8 T cell- and NK cell-mediated immune response resulting in complete and stable remission. Conclusively, this preclinical in-vivo study suggests that Tregs are an attractive target for the treatment of multiple myeloma.
Abstract Cell surface expression levels of GPRC5D, an orphan G protein–coupled receptor, are significantly higher on multiple myeloma (MM) cells, compared with normal plasma cells or other immune cells, which renders it a promising target for immunotherapeutic strategies. The novel GPRC5D-targeting T-cell redirecting bispecific antibody, talquetamab, effectively kills GPRC5D+ MM cell lines in the presence of T cells from both healthy donors or heavily pretreated MM patients. In addition, talquetamab has potent anti-MM activity in bone marrow (BM) samples from 45 patients, including those with high-risk cytogenetic aberrations. There was no difference in talquetamab-mediated killing of MM cells from newly diagnosed, daratumumab-naïve relapsed/refractory (median of 3 prior therapies), and daratumumab-refractory (median of 6 prior therapies) MM patients. Tumor cell lysis was accompanied by T-cell activation and degranulation, as well as production of pro-inflammatory cytokines. High levels of GPRC5D and high effector:target ratio were associated with improved talquetamab-mediated lysis of MM cells, whereas an increased proportion of T cells expressing PD-1 or HLA-DR, and elevated regulatory T-cell (Treg) counts were associated with suboptimal killing. In cell line experiments, addition of Tregs to effector cells decreased MM cell lysis. Direct contact with bone marrow stromal cells also impaired the efficacy of talquetamab. Combination therapy with daratumumab or pomalidomide enhanced talquetamab-mediated lysis of primary MM cells in an additive fashion. In conclusion, we show that the GPRC5D-targeting T-cell redirecting bispecific antibody talquetamab is a promising novel antimyeloma agent. These results provide the preclinical rationale for ongoing studies with talquetamab in relapsed/refractory MM.
Abstract Immunosuppressive milieu of multiple myeloma is associated with various cellular and non-cellular factors that foster immune escape leading to tumor progression. While immune checkpoint inhibitors have achieved significant clinical success in many types of solid tumors, recent clinical trials of immune checkpoint blockade performed in patients with multiple myeloma failed to demonstrate significant anti-tumor efficacy. To enhance the clinical efficacy of immune checkpoint blockade in multiple myeloma, elaborate characterization of tumor antigen-specific T cells is an essential prerequisite. In the present study, we investigated the immunophenotypic and functional characteristics of tumor antigen-specific T cells in patients with multiple myeloma. In addition, using direct ex vivo experimental techniques, we tried to examine how to manipulate the immunosuppressive microenvironment to maximize anti-myeloma responses of the tumor-specific T cells. We first tried to define and characterize CD8+ T cell population capable of specifically recognizing and reacting to myeloma cells in bone marrow of myeloma patients using MHC multimer technique. In selected patients, we could successfully define CD8+ T cell population specifically recognizing the HLA-A*0201-restricted epitopes (either "SLLMWITQC" or "LLLGIGILV"), included in myeloma tumor antigens NY-ESO-1 and HM1.24. The vast majority of myeloma-antigen specific CD8+ T cells expressed high level of PD-1 and also co-expressed other types T cell inhibitory receptors. More strikingly, PD-1+ myeloma-specific CD8+ T cells had a distinct pattern of transcriptional factor expression, high level of Eomes and low level of T-bet (EomeshiT-betlo), indicating that they were profoundly exhausted functionally and that a simple blockade of PD-1/PD-L1 binding might not be enough to reinvigorate their anti-myeloma activity. Consistent with the immunophenotypes of myeloma-specific CD8+ T cells, malignant plasma cells in bone marrow of myeloma patients, defined as CD14-CD19-CD138+CS1+CD56hi, also expressed PD-L1 abundantly, compared to normal plasma cells, suggesting that PD-1/PD-L1 axis plays a major role in making myeloma-recognizing T cells unresponsive to TCR stimulation. Interestingly, in addition to tumor cells, various types of immune cells comprising myeloma microenvironment also highly express PD-L1. Indeed, in response to ex vivo TCR stimulation with anti-CD3, CD8+ T cells from myeloma bone marrow showed lower proliferation and reduced production of anti-tumor effector cytokines (INF-γ and TNF-α), compared to marrow-infiltrating CD8+ T cells of diffuse large B cell lymphoma and Hodgkin lymphoma patients with extensive bone marrow involvement. However, even in the presence of anti-PD-1, myeloma-specific responses of marrow-infiltrating CD8+ T cells was only modestly improved in terms of proliferation and cytokine production. Next, we investigated whether blocking TGF-β signaling in combination with PD-1/PD-L1 axis blockade could restore the function of marrow-infiltrating CD8+ T cells of myeloma patients, since TGF-β produced by clonal plasma cells and bone marrow stromal cells is critical in immunosuppressive microenvironment of multiple myeloma. To this end, we found that combination of TGF-β signaling blockade (either anti-TGF-β1 or Galunisertib, a small molecule inhibitor of TGF-β receptor I) with anti-PD-1 significantly increased the frequencies of IFN-γ- and/or TNF-α-producing CD8+ T cells in response to ex vivo TCR stimulation, compared to a single PD-1 or a single TGF-β blockade. Likewise, myeloma antigen-specific proliferation of CD8+ T cells was significantly enhanced with addition of TGF-β signaling blockade. Taken together, although PD-1/PD-L1 axis acts as a major component of immunosuppressive milieu in multiple myeloma, the efficacy of PD-1 blockades in multiple myeloma might be hampered by complicated microenvironment consisting of T cell-intrinsic and -extrinsic factors. Our results provide an ex vivo evidence of incorporating TGF- β signaling blockade to immune checkpoint inhibition to enhance anti-tumor T cell responses in multiple myeloma Disclosures No relevant conflicts of interest to declare.
Activated normal density granulocytes (NDGs) can suppress T-cell responses in a similar way as myeloid-derived suppressor cells (MDSCs). In this study, we tested the hypothesis that NDGs from blood and bone marrow of multiple myeloma (MM) patients have the ability to suppress T-cells, as MDSC. MM is an incurable plasma cell malignancy of the bone marrow. Like most malignancies, myeloma cells alter its microenvironment to promote tumor growth, including inhibition of the immune system. We found that MM NDG from the bone marrow suppressed proliferation of T-cells, in contrast to healthy donors. The inhibitory effect could not be explained by changed levels of mature or immature NDG in the bone marrow. Moreover, NDG isolated from the blood of both myeloma patients and healthy individuals could inhibit T-cell proliferation and IFN-γ production. On the contrary to previous studies, blood NDGs did not have to be preactivated to mediate suppressive effects. Instead, they became activated during coculture, indicating that contact with activated T-cells is important for their ability to regulate T-cells. The inhibitory effect was dependent on the production of reactive oxygen species and could be reverted by the addition of its inhibitor, catalase. Our findings suggest that blood NDGs from MM patients are suppressive, but no more than NDGs from healthy donors. However, only bone marrow NDG from MM patients exhibited MDSC function. This MDSC-like suppression mediated by bone marrow NDG could be important for the growth of malignant plasma cells in MM patients.
