Engineering BCMA CAR T cells for myeloma-targeted cargo delivery – Towards clinical application
Clinical responses with chimeric antigen receptor (CAR) T cells are encouraging, however, primary resistance and relapse after therapy prevent durable remission in a large fraction of cancer patients. One of the underlying causes includes apoptosis resistance mechanisms in cancer cells that limit killing by CAR T cells. For example, elevated expression of pro-survival protein BCL-2 in B lymphoma cells is associated with resistance to CD19 CAR T cells, while CRISPR/Cas9 screens have identified loss of the pro-apoptotic BCL-2 family protein NOXA as another resistance mechanism. We have also shown that expression of granzyme B-inhibitor serpin B9 in B lymphoma cells inhibits killing by CD19 or CD20 CAR T cells, thereby revealing another apoptosis resistance mechanism. In multiple myeloma (MM), high expression of the BCL-2 family protein MCL-1 promotes tumor cell survival. Although MCL-1 inhibition induces rapid cell death in MM cells, systemic inhibition is clinically unfeasible due to toxicity in healthy tissues.
To overcome intrinsic apoptosis resistance and enable tumor-selective inhibition of MCL-1, we developed a CAR T cell platform that delivers the pro-apoptotic protein NOXA directly into cancer cells, coined CARgo T cells.
We reveal that B cell maturation antigen (BCMA) CAR T cells equipped with a granzyme B-NOXA fusion construct improves killing of multiple myeloma (MM) cells, both in vitro and in xenograft mouse models, by localizing NOXA to cytotoxic granules that are released into cancer cells upon contact. Since MM cells critically depend on MCL-1 expression, inhibition by its natural ligand NOXA effectively induces apoptosis. Importantly, NOXA delivery is specific to targeted tumor cells and does not affect CAR T cell viability or harm non-targeted cells, supporting the safety of this strategy.
We are currently advancing the preclinical development of this approach by engineering a panel of BCMA-NOXA CAR constructs with varying configurations. These will be systematically evaluated for efficacy and potential toxicity compared to conventional BCMA CAR T cells. This strategy holds promise for improving CAR T cell function through targeted apoptotic cargo delivery and may be broadly applicable to other malignancies characterized by apoptosis resistance mechanisms.