Oncolytic vaccines, which consist of recombinant oncolytic viruses (OV) encoding tumor-associated antigens (TAAs), have demonstrated potent antitumor efficacy in preclinical models and are currently evaluated in phase I/II clinical trials. On one hand, oncolysis of OV-infected malignant entities reinstates cancer immunosurveillance. On the other hand, overexpression of TAAs in infected cells further stimulates the adaptive arm of antitumor immunity. Particularly, the presence of tumor-specific CD8+ T lymphocytes within the tumor microenvironment, as well as in the periphery, has demonstrated prognostic value for cancer treatments. These effector CD8+ T cells can be detected through their production of the prototypical Tc1 cytokine: IFN-γ. The quantitative and qualitative assessment of this immune cell subset remains critical in the development process of efficient cancer vaccines, including oncolytic vaccines. The present chapter will describe a single-cell immunological assay, namely the intracellular cytokine staining (ICS), that allows the enumeration of IFN-γ-producing TAA-specific CD8+ T cells in various tissues (tumor, blood, lymphoid organs) following oncolytic vaccination.
Keywords: Cancer vaccine; Flow cytometry; IFN-γ; Intracellular cytokine staining (ICS); Oncolytic virus; Tumor antigen.