Developing potent HIV-specific CAR T cells through optimizing antigen sensitivity

PROJECT SUMMARY Given the inability of the immune response to consistently suppress HIV without antiretroviral therapy and the insufficient potency of current cure approaches, genetic engineering modalities may offer a potent alternative to intrinsic immunity. Chimeric antigen receptor (CAR) T cells have shown impressive efficacy in eliminating blood cell cancers in the clinic, and CAR T cells re-engineered to target HIV using the CD4 ectodomain represent a potent escape-resistant cellular therapy demonstrated to have enhanced cytolytic function. Our prior work has demonstrated that when engineered to express both the 4-1BB and CD28 costimulatory domains and protected from HIV infection, HIV-specific CD4 ectodomain CAR T cells can reduce acute viremia, prevent CD4+ T cell loss, and reduce viral burden in the tissues of HIV-infected humanized mice. However, the of reduction plasma viral loads was ultimately transient, suggesting that the potency of HIV-specific CAR T cells should be further optimized for clinical translation. We propose that low expression of HIV Envelope (Env) on HIV-infected cells yields targets with low antigen density. Our preliminary data demonstrates that the potency of CD4 ectodomain CARs is severely attenuated in instances of low antigen density. We reason that this necessitates the design of HIV-specific CAR T cells with enhanced antigen sensitivity. As the characteristics dictating antigen sensitivity are not yet fully described for CAR T cells, we generated a diverse panel of broadly neutralizing antibody-based CAR T cells, specifically to (1) determine the relationship between epitope accessibility, CAR avidity, and antigen sensitivity on HIV-specific CAR T cell potency and (2) identify orthogonal CAR-driven escape patterns informing optimal multi-specificity CAR products that restrict HIV escape in vivo. The ultimate goal is to generate an enhanced HIV-specific CAR T cell product with the ability to kill HIV-infected cells expressing low levels of antigen in order to improve the translational potential of a CAR T cell approach for a functional HIV cure.