Advanced Clinical Cell Processing Technologies for Adoptive T Cell Therapy

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. In experimental animal models we could show that even the transfer of a single memory stem T cell can be enough to reconstitute protective immunity, demonstrating the therapeutic power of distinct T cell subsets. In order to enrich defined T cell populations for clinical applications, we have developed clinical multi-parameter enrichment technologies, and transferred these to GMP-conform cell separation units. A first proof-of-concept clinical trial (treatment of CMV infection in patients upon allogeneic hematopoetic stem cell transplantation with donor-derived antigen-specific T cells) has just been finished and confirmed that therapeutic adoptive transfer of low numbers of highly purified antigen-specific T cells (without any further in vitro culture) is clinically safe and confers specific immunity to infection.

Infusing a T cell product containing memory stem cells can be highly effective therapeutically, but might also bear some risk of toxicity. Therefore, safeguards that allow selective depletion of transferred cells in the case of un-tolerable side effects may be needed. In this context, we explored the capacity of a truncated version of Epidermal Growth Factor Receptor (EGFRt) co-expressed with adoptively transferred T cells. EGFRt is functionally inert, as it cannot bind EGFR-ligands and lacks signaling components, and is non-immunogenic. However, it still binds to Cetuximab, an EGFR-specific antibody already used for clinical applications. We can show in a pre-clinical animal models that EGFRt-expressing engineered T cells can be effectively depleted via Cetuximab treatment in vivo. For example, B cell aplasia (lack of B lymphocytes), which is a common long-lasting side effect of CD19 CAR-T cell treatment, can be reverted by antibody-mediated in vivo depletion.