Improving Anti-BCMA CAR-T Functionality with Novel Celmods in Multiple Myeloma

Background: Anti-B Cell maturation antigen (BCMA) targeting Chimeric Antigen Receptor T Cells (CAR-T) has high response rates in relapsed Multiple myeloma (MM) and more recently approved for earlier lines of disease. However not all patients are cured after CAR-T therapy and new approaches are needed to improve outcomes for patients receiving cellular therapy for MM. Our group has published the ability of novel CELMoDs, Iberdomide and Mezigdomide, to increase activation of T and NK cells while reducing exhaustion markers (TIGIT) in MM patients (Oekelen et al, Cell Reports Medicine 2024, Chen et al ASH 2023). Based on this, we hypothesize that CELMoDs can improve anti-BCMA CAR-T function and ultimately clinical outcomes.

Methods: We evaluated the impact of novel CELMoDs Iberdomide and Mezigdomide on the persistence, proliferation, and activation of healthy donor derived Anti-BCMA CAR-T cells. Using custom 40-color spectral flow cytometry panels, we investigated the dynamics of the CAR-T cell phenotypic makeup and proliferation in response to CELMoD administration. In addition, we investigated the functional effect of CELMoDs on CAR-T cells by measuring antigen-specific cytokine production and cytotoxic activity.

Results: Our results demonstrate that the addition of Iberdomide and Mezigdomide significantly decreases the protein levels of transcription factors Ikaros and Aiolos in CAR-T cells by 24 hours (p<0.01). Addition of CELMoDs promoted persistence and increased viability in IL-2 starved CAR-T cells in vitro. After prolonged culture, CAR-T cells treated with CELMoDs were significantly more viable compared to control (median viability 82% compared to 45%, p<0.001). Iberdomide almost doubled the presence of hallmark activation markers such as HLA-DR, and CD69 (p<0.05) while Mezigdomide tripled the presence of hallmark activation markers such as HLA-DR, and CD69 (p<0.001). CELMoDs increased antigen specific cytokine production of IL-2, IL-17a, and TNFa by CD8+ and CD4+ CAR-T cells against BCMA expressing MM cells (p<0.01). CELMoDs enhanced antigen specific toxicity by CAR-T cells by 46% compared to control by 24 hours (p<0.05). Early incorporation of CELMoDs during the transduction of CAR-T cells doubled the production of CAR-T cells that remained in an effector memory phenotype. These findings suggest that incorporation of CELMoDs can keep CAR-T cells in an activated state counteracting exhaustion and promote the survival and function of CAR-T cells.

Conclusion: Our results provide evidence for the beneficial effect of combinational treatment with CELMoDs which can enhance the persistence and proliferation of anti-BCMA CAR-T cells in vitro. Moreover, CELMoDs increased the activation of CAR-T cells leading to improved antigen specific cytokine production and cytotoxic activity. Our findings highlight the potential of CELMoDs as an adjunctive therapy to improve CAR-T cell persistence and reduce exhaustion, overall improving the therapeutic efficacy of anti-BCMA CAR-T therapy in patients with MM. We are planning further studies to test these promising results in vivo, with the goal of translating them into clinical trials for improving outcomes for MM patients.