Session: 652. Myeloma: Pathophysiology and Pre-Clinical Studies, excluding Therapy: Novel Immunotherapeutic Strategies in Multiple Myeloma
Methods: The function of UCARTCS1 cells was tested in vitro against MM cell line (MM.1S) and primary MM tumor cells using flow-cytometry-based cytotoxicity, degranulation, CFSE proliferation, and multiplex cytokine induction assays. The efficacy of UCARTCS1 was also tested in vivo against primary MM xenografts in human fetal bone implanted into NOD/SCID/IL2rgnull mice (NSG-hu). Double KO (TRAC and SLAMF7) T-cells lacking SLAMF7 CAR served as controls. The potential toxicity of UCARTCS1 against hematopoietic cells has also been assessed in vitro using the cytotoxicity assay.
Results: UCARTCS1, but not control double KO T-cells, specifically lysed MM.1S (median, 93% lysis; range, 78-98% with UCARTCS1 vs. median, 17%; range, 15-47% with control T-cells; n=10 experiments) and primary MM tumor cells (n=10 samples) (median 59%; range, 20-90% with UCARTCS1 vs. median 9%; range, 0-36% with control T cells). 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 showed that UCARTCS1 cells primarily produced IFN-γ and GM-CSF in presence of primary MM tumor cells (n=6) suggesting a Th1/Tc1 response. On the other hand, UCARTCS1 did not induce any significant lysis of normal donor peripheral blood mononuclear cells or CD34+ hematopoietic cells from bone marrow aspirates of healthy donors.
To test the efficacy of UCARTCS1 cells in vivo we injected 1x106 CD138-purified primary MM tumor cells into the NSG-hu mouse model. After the tumor had been established (6-8 weeks with a serum M-protein level >15 µg/ml), mice were treated intravenously with a single injection of 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 studies revealed that UCARTCS1 cells specifically target and lyse primary MM tumor cells both in vitro and in vivo. Further, UCARTCS1 cells specifically degranulated, produced Th1/Tc1 cytokines, and proliferated in response to primary MM tumor cells. Our results support further development and testing of this universal “off-the-shelf” allogeneic SLAMF7-specific CAR-T product in patients with MM.
Disclosures: Galetto: Cellectis SA: Employment. Gouble: Cellectis SA: Employment. Filipe: Cellectis: Employment. Gariboldi: Cellectis SA: Employment. Thomas: Celgene: Research Funding; Bristol Myers Squibb: Research Funding. Lee: Daiichi Sankyo: Research Funding; Celgene: Consultancy; Takeda: Consultancy. Patel: Juno: Consultancy; Celgene: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding. Smith: Cellectis: Employment. Yang: Poseida Therapuetics: Research Funding; Cellectis: Research Funding. Neelapu: Cellectis Inc.: Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Karus: Research Funding; Bristol-Myers Squibb: Research Funding; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kite Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Poseida Therapeutics, Inc: Research Funding.
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