Redirecting switchable UniCAR T cells for elimination of radioresistant cancer cells

Radiation therapy represents a commonly applied treatment regimen for solid tumors. Unfortunately, it is often accompanied by a high risk for the outgrowth of radioresistant cancer cells against which treatment options are limited. We challenged the idea whether or not chimeric antigen receptor (CAR)-modified T cells could be exploited as an adjuvant immunotherapy in combination with standard radiotherapy. Over the past several years, we have established switchable universal CAR constructs (UniCARs) that recognize a short peptide epitope (E5B9) which does not exist on the surface of living cells. UniCAR T cells are redirected to malignant cells exclusively in the presence of a target module (TM) that contains the epitope E5B9 and specifically binds to a tumor-associated antigen (TAA) on the tumor cell surface.
For providing a rationale for the combination of CAR and radiation therapy, we used different radioresistant sublines of the head and neck cancer cell line Cal33. Expression of various TAAs including of PSCA, EGFR and CD98 was confirmed by flow cytometry analysis. Subsequently, TMs recognizing these potential targets were generated from the variable domains of monoclonal antibodies, cloned into lentiviral vectors and purified from cell culture supernatants of TM-producing stable cell lines. In parallel, T cells isolated from healthy donors were engrafted with UniCARs by lentiviral transduction. Armed with our anti-TAA TMs, UniCAR T cells efficiently lysed radioresistant Cal33 tumor cells both in vitro and in vivo.
Taken together, we could demonstrate that radioresistant cancer cells can effectively be killed by retargeting UniCAR T cells against PSCA, CD98 and EGFR. Thus, resistance to standard of care radiotherapy can be overcome by concomitant or subsequent immunotherapy using the flexible UniCAR technology.