BCMA- and CST6-specific CAR T cells lyse multiple myeloma cells and suppress murine osteolytic lesions

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Abstract

We have previously demonstrated that cystatin E/M (CST6), which is elevated in a subset of patients with multiple myeloma (MM) lacking osteolytic lesions (OLs), suppresses MM bone disease by blocking osteoclast differentiation and function. CST6 is a secreted type 2 cystatin, a cysteine protease inhibitor that regulates lysosomal cysteine proteases and the asparaginyl endopeptidase legumain. Here, we developed B cell maturation antigen (BCMA) CST6 chimeric antigen receptor T cells (CAR-T cells), which lysed MM cells and released CST6 proteins. Our in vitro studies show that these CAR-T cells suppressed the differentiation and formation of tartrate-resistant acid phosphatase–positive (TRAP+) osteoclasts. Using xenografted MM mice, bioluminescence images showed that both BCMA–CAR-T and BCMA–CST6–CAR-T cells inhibited MM growth to a similar extent. Reconstructed micro–computed tomography images revealed that BCMA–CST6–CAR-T cells, but not BCMA–CAR-T cells, prevented MM-induced bone damage and decreased osteoclast numbers. Our results provide a CAR-T strategy that targets tumor cells directly and delivers an inhibitor of bone resorption.

Authors

Fumou Sun, Yan Cheng, Jin-Ran Chen, Visanu Wanchai, David E. Mery, Hongwei Xu, Dongzheng Gai, Samer Al Hadidi, Carolina Schinke, Sharmilan Thanendrarajan, Maurizio Zangari, Frits van Rhee, Guido Tricot, John D. Shaughnessy Jr., Fenghuang Zhan