Targeting of tumor antigen CD38 and stress antigens MICA/B by CAR T cells provides a unique approach for the comprehensive treatment of multiple myeloma

Abstract

Abstract Introduction: Recently approved autologous chimeric antigen receptor (CAR) T-cell therapies (Abecma® and Carvykti®) have demonstrated clear clinical benefit for patients with relapsed/refractory multiple myeloma (MM) with initial response rates ranging between 73-98%. Unfortunately, many of these patients ultimately relapse, often as the result of antigen shedding and tumor heterogeneity, tumor microenvironment suppression, and poor CAR T-cell functional persistence, highlighting the need for alternative therapies that can simultaneously mitigate and overcome these tumor-intrinsic and -extrinsic challenges. Furthermore, broad patient access of patient- and donor-derived CAR T cells are limited by manufacturing challenges and the use of conditioning chemotherapy. Methods FT836 is an iPSC-derived CAR T cell that uniquely targets the conserved α3 domain of the inducible stress ligands MICA/B, enabling broad recognition of both hematologic and solid tumors. The unique engineered elements of FT836 further enable (i) multi-antigen targeting by antibody-dependent cellular cytotoxicity (ADCC) in combination with the high-affinity non-cleavable CD16a Fc receptor (hnCD16) and therapeutic monoclonal antibodies (e.g. sarclisa and daratumumab), (ii) functional persistence in an allogeneic setting without the reliance on conditioning chemotherapy using dual Sword and ShieldTM engineering, incorporating a synthetic alloimmune defense receptor (ADR) that selectively eliminates 4-1BB+ alloreactive immune cells and genetic deletion of CD58 to avoid recognition by host immune cells, and (iii) improved tumor homing and resistance to immunosuppression via expression of the chemokine receptor CXCR2 and the TGFβ signal redirection receptor, respectively. Results Analysis of MM at both the mRNA and protein level revealed MICA/B and CD38 to be highly enriched with comprehensive disease coverage, as demonstrated by i) the Cancer Cell Line Encyclopedia (median Log2(TPM+1) MICA/B: 4.39 and CD38:5.022), ii) primary multiple myeloma patient samples (MMRF-CoMMpass, Skerget et al. 2024; median Log2(TPM+1) MICA/B: 4.23 and CD38: 7.64), and iii) surface expression analysis of a panel of multiple myeloma cancer cell lines, including RPMI-8226, NCI-H929, OPM2, and MM.1s. In vitro cytotoxicity assays exhibited dose-dependent killing in combination with CD38 antibodies (daratumumab and sarclisa), uniquely enabling multi-antigen targeting through both innate and adaptive immunity (CAR+ADCC). Importantly, unlike NKG2D-mediated cytotoxicity, the presence of soluble MICA/B did not impact the anti-tumor efficacy of FT836. In a xenograft model of solid tumor using RPMI-8226, the tumor burden was effectively controlled by FT836 and the depth of response was extended when combined with daratumumab, underscoring the potential for potent and effective control of MM using FT836 by simultaneously targeting MICA/B and CD38 antigens. In a two-way MLR assay against a panel of HLA-mismatched PBMC donors, FT836 limited the generation of alloreactive immune cells (4x, p<0.0005) and demonstrated significantly enhanced functional persistence (21x, p<0001), displaying the utility of Sword and ShieldTM engineering compared to control. Similarly, in the presence of HLA-mismatched PBMCs previously primed to react to product material to represent a supraphysiological allogeneic environment, FT836 demonstrated improved functional persistence (3x, p<0.01), eliminated reactive allogeneic cells (3x, p<0.05), and maintained potent anti-MICA/B CAR-mediated anti-tumor activity compared to control. Conclusion The data demonstrates that FT836 mediates potent and comprehensive control of MM without the need for intense conditioning chemotherapy, and that its depth of coverage can be uniquely enhanced in combination with therapeutics antibodies. As an off-the-shelf CAR T-cell therapy derived from a multiplex-engineered iPSC master cell bank, FT836 is scalable and cost-effective, with the potential to broadly and effectively treat patients with MM.