CAR T cells re-directed by a rationally designed human peptide tag demonstrate efficacy in preclinical models

Currently, only a few chimeric antigen receptor (CAR) T cell therapies have been approved by the Food and Drug Administration and European Medicines Agency for the treatment of B-cell malignancies. To enable broader application of the CAR T cell technology in other indications, improved control and flexible targeting of multiple tumor antigens are required. Here, we developed a novel adapter CAR (AdCAR) T cell platform for flexible targeting of multiple tumor antigens. This platform is based on a short peptide tag derived from an interdomain region of fibroblast growth factor receptor 2 (FGFR2), commonly mutated in cancer. To select AdCARs specific for mutated FGFR2-derived peptide tags, a multistep pooled screening approach in primary T cells was employed, incorporating MACS separation and next-generation sequencing. The resulting AdCAR was highly specific for the FGFR2-derived peptide tag. Using different in vitro and in vivo model systems, the activity of AdCAR T cells was shown to be strictly dependent on the presence of the adapter and corresponding target antigen. Moreover, AdCAR T cells could be redirected to different target antigens by the addition of respective adapter molecules (AM). Finally, in situ expression of functional AM in primary T cells under control of a drug-inducible promoter system was demonstrated, highlighting the potential for controlling the activity of AdCAR T cells by cellular micropharmacies.