Enhanced BCMA Antigen Density Increases Trogocytosis and Attenuates CAR T cell Function

Area of Science:

• Immunotherapy
• Oncology
• Cellular Biology

Background:

• Chimeric Antigen Receptor (CAR) T cell therapy targeting B-cell maturation antigen (BCMA) shows promise for relapsed/refractory multiple myeloma (MM).
• Disease relapse remains a challenge, with trogocytosis (antigen transfer) potentially impairing CAR T-cell function and leading to reduced antigen density.
• The impact of γ-secretase inhibitors (GSI), which increase BCMA density, on trogocytosis and CAR T-cell function is not fully understood.

Purpose of the Study:

• To investigate the effects of GSI on BCMA-directed CAR T-cell function and trogocytosis in multiple myeloma.
• To evaluate the consequences of BCMA acquisition by CAR T cells on their phenotype, function, and susceptibility to fratricide.
• To correlate in vitro findings with clinical data from CAR T-cell therapy trials.

Main Methods:

• In vitro co-culture systems using MM cell lines with varying BCMA expression treated with GSI.
• Confocal microscopy, cytotoxicity assays, and time-resolved functional studies to assess trogocytosis and fratricide.
• Multiparametric flow cytometry, proteomic profiling, single-cell RNA sequencing (scRNA-seq), and TCR sequencing to analyze CAR T-cell phenotypes and functions.
• Analysis of clinical samples from Phase I trials investigating CAR T-cell therapy with or without GSI.

Main Results:

• GSI increased BCMA density, enhancing initial CAR T-cell cytotoxicity but also significantly increasing trogocytosis.
• CAR T cells that acquired BCMA (CAR T Trogo+) showed reduced proliferation, diminished cytotoxic function, and increased exhaustion/activation markers (PD-1, LAG-3, TIM-3, TOX).
• CAR T Trogo+ cells were susceptible to killing by naive CAR T cells (fratricide), and scRNA-seq confirmed heightened activation and accelerated exhaustion.
• Clinical trial data confirmed BCMA trogocytosis in patient samples.

Conclusions:

• Increased BCMA density via GSI has paradoxical effects, enhancing initial tumor targeting while promoting trogocytosis-associated CAR T-cell dysfunction.
• Trogocytosis may lead to antigen modulation, CAR T-cell exhaustion, and fratricide, potentially limiting the therapeutic benefits of increased antigen density.
• Future clinical trials should incorporate early sampling and mechanistic assessments to optimize GSI use and mitigate resistance mechanisms associated with trogocytosis.