Antigen-induced chimeric antigen receptor multimerization amplifies on-tumor cytotoxicity.

Ligand-induced receptor dimerization or oligomerization is a widespread mechanism for ensuring communication specificity, safeguarding receptor activation, and facilitating amplification of signal transduction across the cellular membrane. However, cell-surface antigen-induced multimerization (dubbed AIM herein) has not yet been consciously leveraged in chimeric antigen receptor (CAR) engineering for enriching T cell-based therapies. We co-developed ciltacabtagene autoleucel (cilta-cel), whose CAR incorporates two B-cell maturation antigen (BCMA)-targeted nanobodies in tandem, for treating multiple myeloma. Here we elucidated a structural and functional model in which BCMA-induced cilta-cel CAR multimerization amplifies myeloma-targeted T cell-mediated cytotoxicity. Crystallographic analysis of BCMA-nanobody complexes revealed atomic details of antigen-antibody hetero-multimerization whilst analytical ultracentrifugation and small-angle X-ray scattering characterized interdependent BCMA apposition and CAR juxtaposition in solution. BCMA-induced nanobody CAR multimerization enhanced cytotoxicity, alongside elevated immune synapse formation and cytotoxicity-mediating cytokine release, towards myeloma-derived cells. Our results provide a framework for contemplating the AIM approach in designing next-generation CARs.

Four-year follow-up of LCAR-B38M in relapsed or refractory multiple myeloma: a phase 1, single-arm, open-label, multicenter study in China (LEGEND-2).

BACKGROUND: LCAR-B38M is a chimeric antigen receptor T cell product with two binding domains targeting B cell maturation antigen. Our previous reports showed a remarkable efficacy of LCAR-B38M in patients with relapsed/refractory multiple myeloma (RRMM) at a median follow-up of 2 years. Here, we report long-term safety and efficacy data from a median follow-up of 4 years. METHODS: LEGEND-2 was a phase 1, single-arm, open-label study conducted in four registered sites in China. Seventy-four participants with RRMM received LCAR-B38M treatment. Lymphodepletion was performed using cyclophosphamide or cyclophosphamide plus fludarabine. LCAR-B38M, at a median dose of 0.513 × 106 cells/kg, was intravenously administered either in three split infusions or in a single infusion. The primary objective was the safety of LCAR-B38M, and the secondary objective was efficacy. RESULTS: As of May 25, 2021, the median follow-up was 47.8 months. All patients experienced ≥ 1 adverse events (AEs). Grade ≥ 3 AEs were observed in 45/74 (60.8%) patients. Cytokine release syndrome (CRS) occurred in 68/74 (91.9%) cases; 7 (9.5%) had grade ≥ 3 CRS. One patient experienced grade 1 central nervous system toxicity. The overall response rate was 87.8%. Fifty-four out of 74 (73.0%) patients achieved complete response. The median progression-free survival was 18.0 months, and the median overall survival for all patients was not reached. The median duration of response was 23.3 months. Four patients experienced viral infection more than 6 months post-infusion, and four patients developed second primary non-hematological malignancies at a median time of 11.5 months post-CAR-T cell transfer. CONCLUSIONS: The 4-year follow-up data of LCAR-B38M therapy demonstrated a favorable long-term safety profile and a durable response in patients with RRMM. Trial registration Clinicaltrials.gov NCT03090659 (retrospectively registered on March 27, 2017); ChiCTR-ONH-17012285.

Exploratory trial of a biepitopic CAR T-targeting B cell maturation antigen in relapsed/refractory multiple myeloma.

Relapsed and refractory (R/R) multiple myeloma (MM) patients have very poor prognosis. Chimeric antigen receptor modified T (CAR T) cells is an emerging approach in treating hematopoietic malignancies. Here we conducted the clinical trial of a biepitope-targeting CAR T against B cell maturation antigen (BCMA) (LCAR-B38M) in 17 R/R MM cases. CAR T cells were i.v. infused after lymphodepleting chemotherapy. Two delivery methods, three infusions versus one infusion of the total CAR T dose, were tested in, respectively, 8 and 9 cases. No response differences were noted among the two delivery subgroups. Together, after CAR T cell infusion, 10 cases experienced a mild cytokine release syndrome (CRS), 6 had severe but manageable CRS, and 1 died of a very severe toxic reaction. The abundance of BCMA and cytogenetic marker del(17p) and the elevation of IL-6 were the key indicators for severe CRS. Among 17 cases, the overall response rate was 88.2%, with 13 achieving stringent complete response (sCR) and 2 reaching very good partial response (VGPR), while 1 was a nonresponder. With a median follow-up of 417 days, 8 patients remained in sCR or VGPR, whereas 6 relapsed after sCR and 1 had progressive disease (PD) after VGPR. CAR T cells were high in most cases with stable response but low in 6 out of 7 relapse/PD cases. Notably, positive anti-CAR antibody constituted a high-risk factor for relapse/PD, and patients who received prior autologous hematopoietic stem cell transplantation had more durable response. Thus, biepitopic CAR T against BCMA represents a promising therapy for R/R MM, while most adverse effects are clinically manageable.

A phase 1, open-label study of LCAR-B38M, a chimeric antigen receptor T cell therapy directed against B cell maturation antigen, in patients with relapsed or refractory multiple myeloma.

BACKGROUND: Chimeric antigen receptor (CAR) T cell therapy has demonstrated proven efficacy in some hematologic cancers. We evaluated the safety and efficacy of LCAR-B38M, a dual epitope-binding CAR T cell therapy directed against 2 distinct B cell maturation antigen epitopes, in patients with relapsed/refractory (R/R) multiple myeloma (MM). METHODS: This ongoing phase 1, single-arm, open-label, multicenter study enrolled patients (18 to 80 years) with R/R MM. Lymphodepletion was performed using cyclophosphamide 300 mg/m2. LCAR-B38M CAR T cells (median CAR+ T cells, 0.5 × 106 cells/kg [range, 0.07 to 2.1 × 106]) were infused in 3 separate infusions. The primary objective is to evaluate the safety of LCAR-B38M CAR T cells; the secondary objective is to evaluate the antimyeloma response of the treatment based on the general guidelines of the International Myeloma Working Group. RESULTS: At data cutoff, 57 patients had received LCAR-B38M CAR T cells. All patients experienced ≥ 1 adverse events (AEs). Grade ≥ 3 AEs were reported in 37/57 patients (65%); most common were leukopenia (17/57; 30%), thrombocytopenia (13/57; 23%), and aspartate aminotransferase increased (12/57; 21%). Cytokine release syndrome occurred in 51/57 patients (90%); 4/57 (7%) had grade ≥ 3 cases. One patient reported neurotoxicity of grade 1 aphasia, agitation, and seizure-like activity. The overall response rate was 88% (95% confidence interval [CI], 76 to 95); 39/57 patients (68%) achieved a complete response, 3/57 (5%) achieved a very good partial response, and 8/57 (14%) achieved a partial response. Minimal residual disease was negative for 36/57 (63%) patients. The median time to response was 1 month (range, 0.4 to 3.5). At a median follow-up of 8 months, median progression-free survival was 15 months (95% CI, 11 to not estimable). Median overall survival for all patients was not reached. CONCLUSIONS: LCAR-B38M CAR T cell therapy displayed a manageable safety profile and demonstrated deep and durable responses in patients with R/R MM. TRIAL REGISTRATION: ClinicalTrials.gov , NCT03090659 ; Registered on March 27, 2017, retrospectively registered.