Development of CAR T Cells Expressing a Suicide Gene Plus a Chimeric Antigen Receptor Targeting Signaling Lymphocytic-Activation Molecule F7

Abstract

Chimeric antigen receptors (CARs) are fusion proteins that contain antigen-recognition domains and Tcell signaling domains. Signaling lymphocytic-activation molecule F7 (SLAMF7) is a promising target for CAR Tcell therapies of the plasma cell malignancy multiple myeloma (MM) because SLAMF7 is expressed by MM but not normal nonhematopoietic cells. We designed CARs targeting SLAMF7. We transduced human Tcells with anti-SLAMF7 CARs containing either CD28 or 4-1BB costimulatory domains. Tcells expressing CD28-containing CARs or 4-1BB-containing CARs recognized SLAMF7 invitro. SLAMF7-specific cytokine release was higher for Tcells expressing CARs with CD28 versus 4-1BB domains. In murine solid tumor and disseminated tumor models, anti-tumor activity of Tcells was superior with CD28-containing CARs versus 4-1BB-containing CARs. Because of SLAMF7 expression on some normal leukocytes, especially natural killer cells that control certain viral infections, the inclusion of a suicide gene with an anti-SLAMF7 CAR is prudent. We designed a construct with a CD28-containing anti-SLAMF7 CAR and a suicide gene. The suicide gene encoded a dimerization domain fused to a caspase-9 domain. Tcells expressing the anti-SLAMF7 CAR plus suicide-gene construct specifically recognized SLAMF7 invitro and eliminated tumors from mice. Tcells expressing this construct were eliminated on demand by administering the dimerizing agent AP1903 (rimiducid).