ABSTRACT
Activation of a conditional safety switch has the potential to reverse serious toxicities arising from the administration of engineered cellular therapies, including chimeric antigen receptor (CAR) T cells. The functionally inert, non-immunogenic cell surface marker derived from human epidermal growth factor receptor (EGFRt) is a promising safety switch that has been used in multiple clinical constructs and can be targeted by cetuximab, a clinically available monoclonal antibody. However, this approach requires high and persistent cell surface expression of EGFRt to ensure that antibody mediated depletion of engineered cells is rapid and complete. Here we show that incorporating a short juxtamembrane sequence into the EGFRt polypeptide enhances its expression on the surface of T cells and their susceptibility to antibody-dependent cellular cytotoxicity (ADCC). Incorporating this optimized variant (EGFRopt) into bicistronic and tricistronic CAR designs results in more rapid in vivo elimination of CAR T cells and robust termination of their effector activity compared to EGFRt. These studies establish EGFRopt as a superior safety switch for the development of next-generation cell-based therapeutics.
Competing Interest Statement
S.R.R. is a co-founder of Lyell Immunopharma, Inc. and has received grant funding from Lyell Immunopharma, Inc. S.R.R. was a co-founder Juno Therapeutics, a Bristol Myers Squibb company and has served as a scientific advisor to Juno Therapeutics and Adaptive Biotechnologies. S.P. is an employee of Lyell Immunopharma, Inc. M.J.L. is a co-founder of Lyell Immunopharma, Inc., and Outpace Bio. H.F.M. and M.J.L. are listed as inventors on patent applications related to this work. H.F.M., L.T., and M.J.L. are employees of Outpace Bio, a licensee of patent rights owned by Lyell Immunopharma, Inc. The remaining authors declare no competing interests.
