Abstract LB-254: A universal remedy for CAR T cell limitations

Chimeric antigen receptor (CAR) T cells show significant potential for treating cancer due to their tumor-specific activation and ability to focus their killing activity on cells that express a tumor antigen. Unfortunately, this promising therapeutic technology is still limited by: (1) an inability to control the rate of cytokine release and tumor lysis; (2) the absence of an “off switch” that can terminate cytotoxic activity when tumor eradication is complete; (3) a failure to eliminate tumor cells that do not express the targeted antigen; and (4) a requirement to generate a different CAR T cell for each unique tumor antigen In order to address these limitations, we have exploited a low molecular weight bi-specific adaptor molecule that must bridge between the CAR T cell and its targeted tumor cell by simultaneously binding to the chimeric antigen receptor on the CAR T cell and the unique antigen on the tumor. Using this bispecific adaptor, one can control CAR T cell cytotoxicity by adjusting the concentration and rate of administration of the adaptor. Because the half life of the adapter is To experimentally demonstrate the aforementioned benefits of using low molecular weight bispecific adaptors, CAR T cells were constructed by fusing an anti- fluorescein isothiocyanate (FITC) scFv to a CD3 zeta chain containing the intracellular domain of CD137 (i.e. CAR4-1BBZ T cells). Then, to enable their tumor-specific cytotoxicity, a bispecific adaptor molecule comprised of fluorescein linked to a small organic ligand with high affinity and specificity for a tumor-specific antigen (FITC-SMC) was synthesized. For these studies, the tumor-specific ligands were: i) folate for recognition of the folate receptor that is over-expressed on ∼1/3 of human cancers, ii) DUPA for binding to prostate specific membrane antigen that is over-expressed on prostate cancers, and iii) NK-1R ligand that is over-expressed on neuroendocrine tumors. The ability of the same clone of CAR4-1BBZ T cells to eliminate tumors expressing each of the above antigens was then demonstrated by administration of the desired FITC-SMC to mice injected with the CAR4-1BBZ T cells. Our data show that anti-tumor activity: i) is only induced when both CAR4-1BBZ T cells and the correct antigen-specific FITC-SMC are present, ii) anti-tumor activity and toxicity can be sensitively controlled by adjusting the dosing of FITC-SMC, and iii) treatment of antigenically heterogeneous tumors can be achieved by administration of a mixture of the desired FITC-SMCs. Taken together, these data show that many of the limitations of CAR T cell technology can be addressed by use of a bispecific adaptor molecule to mediate tumor cell recognition and killing. Citation Format: Yong Gu Lee, Haiyan Chu, Srinivasarao Tenneti, Ananda Kumar Kanduluru, Philip S. Low. A universal remedy for CAR T cell limitations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-254.