UC San Diego

The goal of precision immunotherapy is to direct a patient’s T cell response against the immunogenic mutations, or neoantigens (NeoAg), expressed by tumor cells. Most immunotherapy approaches to-date have focused on MHC class I-restricted peptide epitopes by which cytotoxic CD8+ T lymphocytes (CTL) can directly recognize tumor cells. This strategy largely overlooks the critical role of major histocompatibility class II (MHC-II)-restricted CD4+ T cells as both positive regulators of CTL and other effector cell types, and as direct effectors of antitumor immunity. To determine the capacity of tumor-specific CD4+ T cells to directly engage and kill tumor cells, we characterized CD4+ T cells recognizing the oncogenes HPV-16 E6 and KRASG12V from two distinct human patients with cancer. In both cases, CD4+ T cells were unable to recognize MHC- II+ antigen-expressing tumor cells, suggesting only CD4+ T cells recognizing a limited range of antigens may directly recognize tumor cells. To determine the antitumor mechanisms of NeoAg- specific CD4+ T cells independent of direct tumor recognition, we sorted single CD4+ T cells specific for a mutated clathrin heavy chain epitope (CltcH129Q) expressed by the MHC-II-negative murine squamous cell carcinoma VII (SCC VII) tumor. T cell receptor (TCR) sequencing analysis revealed the presence of four distinct TCR clonotypes and expression of these TCRs in primary cells was sufficient to confer recognition of CltcH129Q. Both low and high avidity CltcH129Q-specific CD4+ T cells were capable of proliferating to similar degrees in response to tumor antigen in vivo and enhancing primary tumor immunity in a CD8+ T cell- and CD40L-dependent manner. ACT with CltcH129Q-specific CD4+ T cells also synergized with cyclophosphamide treatment to reduce tumor burden in mice with established tumors. The findings herein have important implications for the use of NeoAg-specific CD4+ T cells as next generation cellular therapies for solid tumors.