Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Recently, chimeric antigen receptor (CAR) expressing T cells have shown tremendous clinic effects in several cancer patients. However once those genetically modified T cells are adoptively transferred in a patient their reactivity cannot be controlled in case of life-threatening side effects or tumor alterations including antigen loss occur. These limitations encouraged us to develop an on/off switchable universal CAR (UniCAR) platform.
As an optimization of conventional CARs, UniCARs do not bind to a cell surface antigen. In contrast their extracellular single-chain fragment variable (scFv) is redirected to the short peptide epitope E5B9 that is physiologically not presented on the surface of living cells. Consequently the UniCAR T cells are inert. Only in the presence of a target module, that exhibits the E5B9 and binds to a tumor surface target, the UniCAR T cells can be cross-linked to tumor cells and thus get activated to kill them. Recently, we have produced a series of monospecific and bispecific target modules against a series of tumor associated antigens including PSCA, PSMA, CD33, CD123, GD2, and EGFR.
Here we demonstrate in vitro as well as in experimental mice that all these target modules are able to efficiently redirect UniCAR T cells against tumor cells in a strictly target-dependent and target-specific manner. Tumor cell killing occurred at pM target module concentrations and the killing efficacy of UniCAR T cells was comparable to conventional CAR T cells. As measured by ELISA and/or flow cytometry-based multiplex assays redirected UniCAR T cells released pro-inflammatory cytokines including for example TNF, IL-2 and IFN-γ but not IL-6. Bispecific tumor targeting mediated superior tumor cell killing effects than the usage of monospecific target modules whereas the amount of released pro-inflammatory cytokines were not increased. Finally, we have proven that redirected UniCAR T cells can kill luciferase-positive tumor cells in immunodeficient mice. In agreement with the UniCAR concept, target modules showed a very short half-life in peripheral blood, could accumulate in established tumors and were released from UniCAR-target module-complexes in a concentration-dependent manner as measured by dynamic PET analysis in mice.
In summary, we established a controllable UniCAR platform for tumor immunotherapy. The reactivity of UniCAR armed T cells can be switched on and off in the presence or absence of target modules and can be regulated in a dose-dependent manner providing an improved safety of the CAR technology. Moreover a variety of different target modules against a series of different tumor targets can be introduced in the UniCAR platform supporting its high flexibility.