Abstract 4190: Combining dual CAR iPSC-derived immune cells with antibody for multi-antigen targeting to overcome clonal resistance in multiple myeloma

Abstract Resistance to CAR-T cell therapy through antigen loss and clonal heterogeneity is a major limiting factor in achieving durable responses, even in highly persistent cell therapies. Simultaneous targeting of multiple tumor antigens with a single therapeutic modality offers the potential to treat heterogeneous tumor populations, prevent antigen escape, and induce durable clinical remission. Here, we demonstrate the application of a unique dual-CAR approach simultaneously targeting two tumor associated antigens (TAA) for the treatment of multiple myeloma (MM) using an off-the-shelf induced pluripotent stem cell (iPSC) derived NK cell platform. The iPSC background has been functionally enhanced and can be combined with therapeutic antibodies. A CAR targeting B cell maturation antigen (BCMA), a well-defined TAA in MM, was designed utilizing a previously published high-affinity binding sequence shown to exhibit high selectivity to BCMA with enhanced recognition of low-BCMA expressing myeloma cells (Bluhm et al., Molec Ther 2018). This CAR was combined with a companion CAR targeting the pan-TAAs, MICA and MICB. The CAR binding sequence targets the conserved α3 domain of MICA/MICB, which we have previously shown to inhibit MICA/B shedding by blocking the putative cleavage site (Andrade et al., Science 2018). The designed anti-MICA/B-α3 CAR exhibits selective targeting potential against a broad range of tumor types. To determine the suitability of co-targeting BCMA and MICA/B in MM, we surveyed surface expression of BCMA and MICA/B on a variety of MM cancer cell lines and observed a complimentary pattern of co-expression compatible with a dual-CAR to broaden the targeting approach of malignant plasma cells. In a reductionist approach, dual CAR-iNK cells exhibited antigen-specific activation, degranulation and cytotoxicity against a Nalm6 target line constitutively expressing the BCMA and MICA/B. Similar trends were observed in a series of long-term cytotoxicity assays against several MM lines, consistent with antibody staining on target cells, illustrating that co-targeting of MICA/B and BCMA expands the breadth of coverage against MM. Known modulators of antigen expression were tested for their ability to provide further depth of response, and therapeutic antibodies such as anti-CD38 were tested in combination to exploit the non-cleavable CD16 and CD38KO edits in the iPSC backbone. These combinations were further tested in vivo against a disseminated model of multiple myeloma where BCMA/MICA dual CAR-iNK cells demonstrated superior tumor control relative to single-CAR controls, and TGI was augmented with the addition of Daratumamab. These data highlight the applicability of a multi-targeted approach in MM patients, whereby MM dual-CAR NK and/or T cells maintain responsiveness to malignant cells that shed or downregulate tumor antigens to evade treatment. Citation Format: Ketan Mathavan, John Reiser, Sajid Mahmood, Yijia Pan, Bryan Hancock, Robert Blum, Wen-I Yeh, Andrew Houk, Chia-Wei Chang, Tom Lee, Bobby Goulding, Jode Goodridge, Ryan Bjordahl, Bahram Valamehr, Uta Hoepken, Armin Rehm, Kai Wucherpfennig. Combining dual CAR iPSC-derived immune cells with antibody for multi-antigen targeting to overcome clonal resistance in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4190.