Abstract PR01: Targeting multiple myeloma with universal SLAMF7-specific CAR T-cells

Background : Recent studies with autologous chimeric antigen receptor (CAR)-redirected T-cells against CD19 have demonstrated long-term durable remissions in patients with B-cell leukemia and lymphoma, indicating that CAR T-cell therapy is a promising approach for refractory malignancies. Signaling lymphocytic activation molecule F7 (SLAMF7, also called CS1) is highly expressed on multiple myeloma (MM) tumor cells and is present in only a subset of hematopoietic cells among normal tissues. Because of its high expression on MM tumor cells and restricted expression in normal cells, SLAMF7 is a potential target for CAR T-cell therapy approach in MM. We had previously demonstrated that allogeneic “off-the-shelf” CAR T-cells lacking the ability to induce graft versus host disease could be generated for universal use by inactivating the TCRα constant (TRAC) gene using TALEN® gene editing technology. We also demonstrated that to minimize the risk of fratricide of SLAMF7-specific CAR+ T-cells, SLAMF7 could be inactivated by TALEN® in the T-cells prior to introduction of the CAR construct (Galetto et al., ASH 2015, Abstract 116). Here, we report the efficacy of these double KO (TRAC and SLAMF7) SLAMF7-specific universal CAR T cells (UCARTCS1) against MM in in vitro and in vivo studies. Methods : We tested the efficacy of UCARTCS1 cells against MM cell lines and primary tumor cells from MM patients for their capacity to specifically a) degranulate when co-cultured with MM tumor cells as determined by CD107a assay, b) lyse MM cell lines and primary MM cells in in vitro cytotoxicity assay, c) produce cytokines in culture supernatants, d) proliferate in presence of MM cells as determined by CFSE proliferation assay, and e) eradicate primary MM tumors in a patient-derived xenograft model as determined by serum tumor immunoglobulin (M-protein) levels and survival analysis. Results : UCARTCS1 but not control double KO T-cells (lacking SLAMF7 CAR) specifically lysed the MM cell line, MM.1S (median, 93% lysis; range, 78-98% with UCARTCS1 vs. median, 17%; range, 15-47% with control T-cells; n=10). UCARTCS1 cells similarly induced significant lysis of tumor cells from primary MM samples (n=10) (median 59%; range, 20-90%) compared to control T cells (median 9%; range, 0-36%). In agreement with this, we observed specific degranulation in both CD4+ and CD8+ UCARTCS1 cells but not control T-cells in presence of MM.1S cells and primary MM tumor cells. In addition, significant and specific proliferation of both CD4+ and CD8+ UCARTCS1 cells but not control T-cells was observed when they were co-cultured with MM.1S or primary MM tumor samples (n=8). Analysis of culture supernatants for ten cytokines (IFN-γ, GM-CSF, IL-2, IL-4, IL-5, IL-6, IL-10, IL-13, IL-17, and TNF-α) showed that UCARTCS1 cells primarily produced IFN-γ and GM-CSF in presence of primary MM tumor cells (n=6), indicating a Th1/Tc1 response. To test the efficacy of UCARTCS1 cells in vivo, we injected 1x106 primary MM tumor cells into human fetal bone implanted under the skin of NSG mice. After the tumor has been established for 6 to 8 weeks and the serum M-protein was sufficiently elevated, mice were treated intravenously with either 10x106 total cells/mouse of UCARTCS1 or control T-cells. Mice treated with control T-cells developed gradual increase in M-protein levels (median, 339 µg/ml; range, 100-700 µg/mL) whereas the M-protein levels rapidly became undetectable in the mice treated with UCARTCS1 cells and remained undetectable until they were euthanized at approximately 50 days after adoptive transfer. Conclusion : Our results demonstrated that UCARTCS1 cells were highly cytotoxic against primary MM tumor cells in both in vitro and in vivo studies. In addition, UCARTCS1 cells specifically degranulated, produced Th1/Tc1 cytokines, and proliferated in response to primary MM tumor cells. These data provide a rationale for evaluating UCARTCS1 cells as a universal “off-the-shelf” allogeneic CART product in patients with MM. This abstract is also being presented as Poster A46. Citation Format: Rohit Mathur, Zheng Zhang, Jin He, Roman Galetto, Agnes Gouble, Isabelle Chion-Sotinel, Stephanie Filipe, Annabelle Gariboldi, Tanooha Veeramachaneni, Elisabet Manasanch, Sheeba Thomas, Hans C. Lee, Krina Patel, Donna Weber, Richard Eric Davis, Robert Orlowski, Julianne Smith, Jing Yang, Sattva S. Neelapu. Targeting multiple myeloma with universal SLAMF7-specific CAR T-cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr PR01.