Defining an Optimal Dual-Targeted CAR T-cell Therapy Approach Simultaneously Targeting BCMA and GPRC5D to Prevent BCMA Escape–Driven Relapse in Multiple Myeloma

Abstract

Chimeric antigen receptor (CAR) T-cell therapy for multiple myeloma targeting B-cell maturation antigen (TNFRSF17; BCMA) induces high overall response rates; however, relapse occurs commonly. A reservoir of multiple myeloma cells lacking sufficient BCMA surface expression (antigen escape) may be implicated in relapse. We demonstrate that simultaneous targeting of an additional antigen—here, G protein-coupled receptor class-C group-5 member-D (GPRC5D)—can prevent BCMA escape–mediated relapse in a model of multiple myeloma. To identify an optimal approach, we compare subtherapeutic doses of different forms of dual-targeted cellular therapy. These include; (i) parallel-produced and pooled mono-targeted CAR T cells, (ii) bicistronic constructs expressing distinct CARs from a single vector, and (iii) a dual-scFv “single-stalk” CAR design. When targeting BCMA-negative disease, bicistronic and pooled approaches had the highest efficacy, whereas for dual-antigen–expressing disease, the bicistronic approach was more efficacious than the pooled approach. Mechanistically, expressing two CARs on a single cell enhanced the strength of CAR T-cell/target cell interactions. Significance: Myeloma frequently relapses post-CAR T-cell therapy; antigen escape–mediated relapse can be mitigated with upfront dual-targeting (BCMA/GPRC5D). A bicistronic vector encoding two CARs avoids the challenge of parallel manufacturing separate CAR T-cell products, while providing superior efficacy; this dual-targeted approach may enhance the durability of responses to cellular therapy for myeloma. See related commentary by Simon and Riddell, p. 130. This article is highlighted in the In This Issue feature, p. 127