CAR Density Influences Antitumoral Efficacy of BCMA CAR T cells and Correlates with Clinical Outcome

Identification of new markers associated with long-term efficacy in patients treated with CAR T cells is a current medical need, particularly in diseases such as multiple myeloma. In this study we address the impact of CAR density on the functionality of BCMA-CAR T cells. Functional and transcriptional studies demonstrate that CAR T cells with high expression of the CAR construct show an increased tonic signaling with upregulation of exhaustion markers, increased in vitro cytotoxicity but a decrease in in vivo BM infiltration. Characterization of Gene Regulatory Networks using scRNA-seq identified regulons associated to activation and exhaustion upregulated in CARHigh T cells, providing mechanistic insights behind differential functionality of these cells. Finally, we demonstrate that patients treated with CAR T cell products enriched in CARHigh T cells show a significantly worse clinical response in several hematological malignancies. In summary, our work demonstrates that CAR density plays an important role in CAR T activity with significant impact on clinical response.