Choice of Better T-cells for Adoptive Immunotherapy

Adoptive transfer of primary (unmodified) or genetically engineered antigen-specific T cells has demonstrated astonishing clinical results in the treatment of infections and some malignancies. The definition of optimal targets and antigen receptors as well as the differentiation status of transferred T cells are emerging as crucial parameters for generating cell products with predictable efficacy and safety profiles. Our laboratory has demonstrated that defined subsets within the memory CD8⁺ T cell compartment fulfill all key characteristics of adult tissue stem cells and are essential for robust and long-term maintained responses upon adoptive transfer. We have developed clinical multi-parameter enrichment technologies to purify these memory stem cells for clinical applications. In my presentation I will report on the status of ongoing clinical trials using such purified cell products either as a primary T cell population for the treatment of infections upon allogeneic stem cell transplantation or after genetic modification with a CD19 CAR for the treatment of malignancies (collaboration with Stan Riddell, FHCC/Seattle). Infusing small numbers of T cells within a memory stem cell product can be highly effective therapeutically, but bears some risk of toxicity. Therefore, safeguards that allow selective depletion of transferred cells in the case of un-tolerable side effects may be needed to further improve adoptive immunotherapy. I will present results exploring the capacity of a truncated version of EGFR (EGFRt) co-expressed with T cells expressing a CD19-CAR. In pre-clinical mouse models we demonstrate that application of Cetuximab, which binds to EGFRt, confers selective depletion of adoptively transferred CAR-T cells in vivo. Long-term B cell aplasia, which is a main side effect of CD19-CAR T cell therapy, can be completely reverted with this strategy. Vaccination studies upon B cell recovery demonstrate full functionality of antigen-specific antibody formation. EGFRt co-expressing CD19-CAR T cells have been successfully transferred into first human patients, providing the option to test for the first time in a clinical setting whether treatment of B cell aplasia after long-term leukemia remission can be achieved by selective depletion.