Preclinical assessment of LCAR-B38M, a novel BCMA-targeting chimeric antigen receptor (CAR)-T cell therapy in relapsed/refractory multiple myeloma

Multiple myeloma (MM) remains an incurable hematologic malignancy, partly due to its resistant microenvironment to immunotherapy. B-cell maturation antigen (BCMA) is expressed on MM cells and has emerged as a selective antigen that has been targeted by novel treatments for MM. Here, we discuss the in vitro and in vivo assessment of LCAR-B38M CAR-T cells, a novel T-cell therapy containing a 4-1BB co-stimulatory domain and two BCMA-targeting single-domain antibodies (sdAbs, also referred to as VHH domains). Recombinant llama-derived VHH domains of LCAR-B38M CAR-T were generated through phage display. Two individually identified VHH fragments were tandemly linked with a synthetic linker as the BCMA-targeting domain of the CAR. Both VHH domains and LCAR-B38M CAR-T cells demonstrated high binding affinities to BCMA in vitro. LCAR-B38M CAR-T cells selectively bind to human BCMA but not to BCMA from mouse or non-human primates. BCMA is almost exclusively expressed on plasma cells and MM cells. The selectivity and specificity of LCAR-B38M CAR-T cells for BCMA were studied in cell-based co-culture assays with various human tumor cell lines that express BCMA (RPMI8226, a human MM cell line) and do not express BCMA. Results from luciferase-based cytotoxicity assays showed that cytotoxicity and cytokine production of LCAR-B38M CAR-T cells were BCMA antigen dependent. Activity was observed on the human MM cell line, whereas no detectable activity was observed on HEK293-hERG cells or on other BCMA-negative tumor cell lines, such as A549 cells (lung carcinoma). LCAR-B38M CAR-T cells demonstrated BCMA antigen–dependent interferon gamma (IFNγ) release in co-culture with the human MM cell line, compared with un-transduced T-cells when co-cultured at a E/T=20:1 ratio. In addition, LCAR-B38M CAR-T cells did not exhibit IFNγ release in co-culture with any of the BCMA-negative human cell lines. These studies confirmed the specificity and activity of LCAR-B38M CAR-T cells against BCMA-positive cells. In vivo anti-tumor efficacy of LCAR-B38M CAR-T cells was evaluated utilizing a MM-derived luciferase-expressing cell line (RPMI8226.Luc) in NCG mice. LCAR-B38M CAR-T cell–treated mice showed statistically significant tumor reduction (P<0.01) and prolonged survival (P<0.01), with no obvious loss of animal body weight. In general, LCAR-B38M shows high affinity and specificity to human BCMA, with potent on-target anti-tumor activity. A phase 1b/2 clinical study is ongoing in the United States (CARTITUDE-1, NCT03548207 , JNJ-68284528) and a phase 2 confirmatory study has been initiated in China (CARTIFAN-1, NCT03758417).