Abstract 6321: Developing a lenalidomide-inducible safety switch for CAR T cell therapy

Abstract While CAR T cell therapy is a medical breakthrough against various hematological malignancies, yet treatment failures often occur at least in part due to excessive engineered T cell activity leading to severe toxicities. To combat this, strategies pairing CAR T cells with safety systems, for example, suicide switches engineered to induce cell death are being actively pursued. However, existing designs have limited performance characteristics and generally use unapproved small molecule controllers or non-human sequences. To overcome these issues, we have developed a novel suicide switch leveraging the well-tolerated, FDA-approved anti-cancer drug lenalidomide, as a controller of the stability of fusion proteins tagged with a “degron” sequence. Specifically, we engineered a stoichiometric pair of transgenes using the apoptotic DNase pair, caspase activating DNase (CAD) and its degron tagged inhibitor (ICAD-degron). We hypothesized that the overexpressed ICAD-degron could restrain CAD, until lenalidomide treatment degrades ICAD to unleash CAD for apoptosis. We found that our system was stably overexpressed and rapidly induced cell death even at sub-nanomolar concentrations of lenalidomide. A comparison of our design with the frontline safety switch, inducible Caspase 9 in primary human T cells revealed that the lenalidomide-induced suicide switch enabled more complete depletion of engineered cells. We tested the effects of our suicide switch on CAR T cell function and found comparable proliferation and tumor cell cytolysis with fast depletion upon lenalidomide addition. In vivo, lenalidomide suicide switch CAR T cells exhibited similar anti-tumor function as control CAR T cells and were rapidly depleted after drug treatment. In summary, utilizing all human sequences and a clinically approved drug controller, we developed a suicide switch that is well tolerated and can rapidly induce cell death even at sub-therapeutic concentrations of lenalidomide. More broadly, chemogenetic regulation of stoichiometric protein pairs is a generalizable strategy for post-translational control of highly active transgenic elements. Citation Format: Ditsa Sarkar, William Lin, Joanna Y. Kim, Nelson H. Knudsen, Isabel C. Lane, Tamina Kienka, Michael C. Kann, Amanda A. Bouffard, Andy Cheng, Marcela V. Maus, Robert T. Manguso, Max Jan. Developing a lenalidomide-inducible safety switch for CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6321.