Anti–G Protein–Coupled Receptor, Class C Group 5 Member D Chimeric Antigen Receptor T Cells in Patients With Relapsed or Refractory Multiple Myeloma: A Single-Arm, Phase Ⅱ Trial

G protein–coupled receptor, class C group 5 member D (GPRC5D) is considered to be a promising surface target for multiple myeloma (MM) immunotherapy. Here, we report the efficacy and safety of anti-GPRC5D chimeric antigen receptor (CAR) T cells in patients with relapsed or refractory (R/R) MM. METHODS: This phase Ⅱ, single-arm study enrolled patients (18-70 years) with R/R MM. Lymphodepletion was performed before patients received 2 × 10(6)/kg anti-GPRC5D CAR T cells. The primary end point was the proportion of patients who achieved an overall response. Safety was also evaluated in eligible patients. RESULTS: From September 1, 2021, to March 23, 2022, 33 patients were infused with anti-GPRC5D CAR T cells. At a median follow-up of 5.2 months (range, 3.2‐8.9), the overall response rate was 91% (95% CI, 76 to 98; 30 of 33 patients), including 11 (33%) stringent complete responses, 10 (30%) complete responses, four (12%) very good partial responses, and five (15%) partial responses. Partial responses or better were observed in nine (100%) of nine patients with previous anti–B-cell maturation antigen (BCMA) CAR T-cell therapy, including two patients who had received repeated anti-BCMA CAR T-cell infusions with no responses at the last time. Grade 3 or higher hematologic toxicities were neutropenia (33 [100%]), anemia (17 [52%]), and thrombocytopenia (15 [45%]). Cytokine release syndrome occurred in 25 (76%) of 33 patients (all were grade 1 or 2), and neurotoxicities in three patients (one grade 2 and one grade 3 ICANSs and one grade 3 headache). CONCLUSION: Anti-GPRC5D CAR T-cell therapy showed an encouraging clinical efficacy and manageable safety profile in patients with R/R MM. For patients with MM that progressed after anti-BCMA CAR T-cell therapy or that is refractory to anti-BCMA CAR T cell, anti-GPRC5D CAR T-cell therapy might be a potential alternative option.