Sensitization of tumor cells for T cell mediated eradication through targeted delivery of virus-derived immunogenic peptide epitopes

The work presented in this thesis aimed at the development of antibody immunoconjugates for the delivery in tumor cells of highly immunogenic T cell epitopes that mediate the antigen-specific recognition by tumoricidal T cells. For this purpose, antibody-targeted pathogen-derived peptides (ATPPs) were generated by conjugating immunodominant, cysteine-containing MHC class I peptides from Epstein-Barr or Influenza A virus to tumor antigen-specific antibodies via a disulfide bond. The integral membrane protein CUB domain-containing protein 1 (CDCP1) was chosen as proof of concept target, as it is upregulated on various cancer types and known to efficiently internalize after antibody binding. After binding to the target and subsequent internalization of ATPPs, fluorescence resonance energy transfer (FRET) imaging revealed that delivered peptides are released upon disulfide reduction in an early endosomal compartment, where they can be loaded into recycling MHC class I complexes. Transport of these MHC-peptide complexes to the cell surface triggers activation of human peptide-specific cytotoxic CD8+ T cells as revealed by interferon-γ ELISA and ELISPOT. Moreover, peptide-specific CD8+ T cells from human donors efficiently lysed ATPP-treated tumor cell lines of various cancer types in a target-dependent manner in vitro. Importantly, targeting of different tumor antigens (e.g. CD138) was equally efficient. The possibility to utilize various peptides with differing HLA-restrictions further highlights the broad applicability of the ATPP approach for T cell mediated targeting of cancer. The usage of a non-cleavable construct or an extended peptide that can not bind to MHC class I molecules additionally revealed the importance of disulfide-dependent peptide release and epitope delivery independent of the classical MHC class I antigen processing pathway. In vivo, ATPPs mediated approximately 60% tumor growth inhibition of established, PD-L1 expressing MDA-MB231 xenografts after 3 weeks of treatment in combination with αPD1-mAb therapy and adoptive transfer of human, peptide-specific CD8+ T cells in NOG mice. These data indicate the potential of ATPPs as novel immunotherapeutic agents, which can be employed to redirect pre-existing virus-specific memory T cells against cancer. Since the immune response will be directed against an exogenous, viral antigen, ATPP therapy reduces the risk for autoimmune side effects as observed with other immunotherapies. Furthermore, the use of highly immunogenic target epitopes circumvents the limitations of the T cell repertoire directed against tumor-associated auto-antigens. The flexible design of ATPPs allows development of an off-the-shelf repertoire of immunoconjugates comprising immunogenic T cell epitopes encoded by highly prevalent pathogens and presented by various high frequency HLA allotypes, thereby providing a means for T cell mediated tumor targeting in a broad patient population.