Enhanced antitumoral activity of the academic CAR-T ARI0002h against normal and low BCMA-expressing myeloma cells after incorporating a transmembrane CD28 domain.

[BACKGROUND] B-cell maturation antigen (BCMA) is the main target for chimeric antigen receptor (CAR)-T cells in multiple myeloma (MM), demonstrating promising outcomes. However, unlike what happens with CART19 in lymphoblastic leukemia and non-Hodgkin's lymphoma, a high proportion of patients will relapse after CAR-T BCMA therapy due to insufficient antigen expression, low CAR-T cell persistence and/or T-cell exhaustion. In other B cell malignancies, second-generation anti-CD19 4-1BB CARs with CD28-transmembrane domain (TMD) have shown high efficacy and a favorable toxicity profile. We have developed a second-generation CD8α-TM BCMA-4-1BBζ CAR-T product, ARI0002h (Cesnicabtagene-autoleucel) for patients with relapsed/refractory MM. We hypothesized that replacing the TMD of ARI0002h with a CD28-TMD could increase efficacy and reduce tumor escape while maintaining a tolerable toxicity profile.

[METHODS] We generated CAR-T cells using T-cells isolated from buffy coats and evaluated the efficacy and fitness of CAR-Ts at day 8-10 of expansion against several MM cell lines. In vitro analyses included cytotoxicity, proliferation, cytokine secretion, T-cell subset markers, activation and exhaustion profiling, metabolomic assays, and RNA-seq after multiple tumor challenges. In in vivo xenograft studies using NSG mice, with tumor cells expressing GFP-ffLuc, disease progression was monitored weekly via bioluminescence imaging.

[RESULTS] Despite showing similar in vitro performance regarding cytotoxicity, proliferation and cytokine production, ARI2h-TM28 outperforms ARI0002h in a low BCMA expression setting and achieves superior in vivo tumor control and survival in relapse models with antigen downregulation. Furthermore, ARI2h-TM28 showed an optimized metabolic profile, more oxidative and energetic compared with ARI0002h, with downregulation of proinflammatory genes in CD8 T cells, contributing altogether both to reduced exhaustion and increased persistence of the CARs, improving their efficacy in preclinical models.

[CONCLUSIONS] Incorporating a CD28-TMD into the ARI0002h CAR enhances tumor control even in relapse models with downregulation of the target antigen, offering improved long-term disease management. This modification increases potency against MM tumor cell lines with both normal and reduced BCMA expression, demonstrating superior metabolic endurance and in vivo activity.