Abstract A057: Uni-CIDeCAR-T cells: MyD88/CD40-enhanced, Ab-directed CAR incorporating the CaspaCIDe® safety switch
Authors: Duong MyLinh T. , Collinson-Pautz Matthew R. , Foster Aaron E. , Bayle J. Henri , Spencer David M. 
Published: May 2016

Background: While chimeric antigen receptor (CAR)-T immunotherapies are remarkably effective against a subset of leukemias and lymphomas, three current hurdles for broad deployment include lack of regulation once administered to the patient, modest efficacy against solid tumors, and the necessity to make separate GMP vectors for each tumor target.

Methods: We developed two methods that utilize chemical induction of protein dimerization (CID) to regulate the activity of engineered T cells containing a CAR of broad utility. “Uni-iC9CAR” combines Bellicum's caspase-9-based, rimiducid-inducible safety switch, CaspaCIDe, with a first generation CD16/FCGR3A–CAR. Antigen receptor specificity relies on the interaction of the Fc-binding domain of CD16 with various tumor-targeted antibodies. In the “Uni-GoCAR” strategy, signaling domains from MyD88 and CD40 are fused to two copies of FKBPv36 to generate iMC, which is co-expressed with the CD16-based CAR. In each strategy, the same dimerizer, rimiducid, binds to FKBPv36 with sub-nanomolar affinity to cause the activation of signaling molecules with distinct functions and outcomes. Lastly, we generated the “Uni-CIDeCAR” vector that combines the iCaspase-9 and CD16-CAR activities from Uni-iC9CAR with augmented ligand-independent MyD88/CD40 costimulation to generate a potent universal CAR with a rapid and effective suicide gene, activated by the normally bio-inert ligand, rimiducid.

Results: Both Uni-GoCAR and Uni-iC9CAR constructs demonstrated rapid, effective and durable, rituximab-dependent antitumor activity when expressed in human T cells and mixed with Raji B cells as early as 7 days after T cell co-culture at a 1:1 ratio. Additionally, rimiducid induced robust cytokine production, including IL-2 and IL-6, and proliferation in T cells transduced with the Uni-GoCAR vector, which expresses the iMC activation switch. In contrast, co-expression of iC9 in the Uni-iC9CAR vector demonstrated robust rimiducid-dependent T cell apoptosis, thus providing a valuable safety mechanism for clinical applications. Finally, in the enhanced, but regulated, Uni-CIDeCAR vector, iC9 maintains safety in a CD16-CAR that is functionally enhanced by rimiducid-independent, basal MC activity.

Conclusion: We report an improved “universal” CAR-T technology that employs a CD16-based CAR (described by Kudo et al (14) Cancer Res) coupled with Bellicum's costimulatory and safety switches to effectively target tumor cells while providing a broad clinical safety net.

Citation Format: MyLinh T. Duong, Matthew R. Collinson-Pautz, Aaron E. Foster, J. Henri Bayle, David M. Spencer. Uni-CIDeCAR-T cells: MyD88/CD40-enhanced, Ab-directed CAR incorporating the CaspaCIDe® safety switch. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A057.