Drug-regulated CD33-targeted CAR T cells control AML using clinically optimized rapamycin dosing

Chimeric antigen receptor (CAR) designs that incorporate pharmacologic control are desirable, however designs suitable for clinical translation are needed. We designed a fully human, rapamycin-regulated, drug product for targeting CD33+ tumors called dimerization agent regulated immunoreceptor complex (DARIC33). T cell products demonstrated target specific and rapamycin-dependent cytokine release, transcriptional responses, cytotoxicity, and in vivo antileukemic activity in the presence of as little as 1nM rapamycin. Rapamycin withdrawal paused DARIC33-stimulated T cell effector functions, which were restored following re-exposure to rapamycin, demonstrating reversible effector function control. While rapamycin-regulated DARIC33 T cells were highly sensitive to target antigen, CD34+ stem cell colony forming capacity was not impacted. We benchmarked DARIC33 potency relative to CD19 CAR T cells to estimate a T cell dose for clinical testing. In addition, we integrated in vitro and preclinical in vivo drug concentration thresholds for OFF-ON state transitions, as well as murine and human rapamycin pharmacokinetics, to estimate a clinically applicable rapamycin dosing schedule. A phase 1 DARIC33 trial has been initiated (PLAT-08, NCT05105152), with initial evidence of rapamycin-regulated T cell activation and anti-tumor impact. Our findings provide evidence that the DARIC platform exhibits sensitive regulation and potency needed for clinical application to other important immunotherapy targets.