Adoptive transfer of T cells, engineered with antigen-specific receptors, is clinically used against acute lymphoblastic leukemia and certain types of large-B-cell lymphomas. Reliable and efficient use of such T cells against solid tumors has not been established yet. However, adoptive transfer of autologous, tumor infiltrating T cells (TILs) can eradicate established solid tumors in some patients. A limitation with this form of therapy is that isolation and expansion of TILs fails in the majority of patients and success seems to depend on the presence of a mutant neoantigen-specific T cell population in the transferred TIL product. Mutant neoantigen-specific T cells can be found in almost all analyzed cancer types. Furthermore, TCR genes can be isolated from TILs and used for viral transduction of patient‑derived, autologous peripheral blood lymphocytes (PBLs). As of yet, it is unknown how many different TCRs from T cell clonotypes of the polyclonal TIL response are needed to achieve cure. Therefore, the main objective of this thesis was to determine the requirements for mutant neoantigen-specific TCR-transduced T cells to achieve eradication of established solid tumors by adoptive transfer. For this, unmanipulated murine tumors were targeted using TCRs that recognized autochthonous, naturally occurring mutant neoantigens. Using such animal models, it was possible to show that tumors can be eradicated with just two cancer‑specific TCR clonotypes. One TCR had to target the cancer cells directly by recognition of a cancer-specific MHC class I restricted antigen, while the second TCR had to target a MHC class II restricted mutant neoantigen presented by cells of the tumor stroma. It shows that both TCR clonotype are sufficient and essential to achieve tumor rejection because a combination of two TCRs targeting independent MHC class I restricted mutant neoantigens was not as efficient and led to tumor escape even though the tumor that had been targeted was developed from a cancer cell clone, seemingly lacking tumor heterogeneity. Targeting only the tumor stroma with a MHC class II restricted mutant neoantigen‑specific TCR led to tumor destruction followed by long‑term growth arrest but never eradicated the tumor. This effect was caused by regression of tumor vasculature and depended on tumor stroma recognition only. For tumor eradication, direct cancer cell recognition was essential because lack of surface expression of MHC class I molecules by cancer cells led to failure of tumor rejection despite the presence of both TCR clonotypes. These data created the hypothesis that a four cell-type interaction is required for effective elimination of solid tumors and gives insights that simplifications for translation into clinical applications may be possible without sacrificing efficacy for adoptive, mutant neoantigen-specific, TCR-redirected T cell transfer.
