Abstract 1318: Targeting multiple myeloma with BCMA-CAR NK cells expressing a GPRC5D-NKG2D bispecific antibody

Abstract Recently developed therapeutics for multiple myeloma (MM) include targeted therapy, immunomodulatory drugs, and immunotherapy, the latter of which consists of B-cell maturation antigen (BCMA) -CAR cells, bispecific antibodies (BsAbs) to engage T cells. However, challenges including relapse and toxicity still exist. The orphan G protein-coupled receptor, class C group 5 member D (GPRC5D), emerged as a novel target for MM therapy. Therefore, following our established system Cancer Immunol Res PMID: 29769244; Leukemia, PMID: 24067492, we generated a BsAb by fusing anti-GPCR5D single-chain variable fragment (scFv) and an anti-NKG2D scFv (GPRC5D-NKG2D BsAb) in a human IgG4 platform and expressed it from BCMA-CAR and soluble IL15 natural killer (NK) cells (s15. BsAb. BCMA-CAR NK) to address the current known limitations. Our data showed that s15. BsAb. BCMA-CAR NK cells secreted GPRC5D-NKG2D BsAb both in vitro and in vivo. To evaluate the function of GPRC5D- NKG2D BsAb expressed from NK cells in vivo, we treated MM tumor-bearing mice with the purified antibody. The data showed that GPRC5D-NKG2D BsAb demonstrated a significantly better survival effect than saline (P≤0. 01). We tested s15. BsAb. BCMA-CAR NK cells for cytotoxicity against a homogenous tumor cell mode (BCMA + GPRC5D +) and a heterogeneous MM tumor cell model, including 50% BCMA + GPRC5D +, 25% BCMA ─ GPRC5D +, and 25% BCMA + GPRC5D ─ cells. Real-time cell analysis (RTCA) data showed s15. BsAb. BCMA-CAR NK cells killed tumor cells in vitro better than both BCMA-CAR NK cells and empty vector-transduced NK cells in an antigen-dependent manner. To test the efficacy of s15. BsAb. BCMA-CAR NK cells in vivo, we established a heterogeneous MM tumor cell mouse model, by mixing BCMA + GPRC5D + OPM2 cells and BCMA + GPRC5D ─ OPM2 cells at the ratio of 2: 1. MM mice were treated with “off-the-shelf” different construct NK cells. The results showed that s15. BsAb. BCMA-CAR NK cells significantly prolonged survival compared to other NK cells (s15. BsAb. BCMA-CAR vs. BCMA-CAR P = 0. 0012). Our data demonstrated that this all-in-one, multifaceted modality provides 2 ready-to-use biologics simultaneously, CAR NK cells and BsAb, for MM treatment. Citation Format: Lei Tian, Victoria Chen, Tasha Barr, Zhiyao Li, Yuqing Chen, Jiaying Zhang, Michael A. Caligiuri, Jianhua Yu. Targeting multiple myeloma with BCMA-CAR NK cells expressing a GPRC5D-NKG2D bispecific antibody abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1318.