Understanding the response to immunotherapy in humans

Whether the efforts of the last decade aimed at the development of vaccines against tumor-specific antigens encountered success or failure is a matter of expectations. On the bright side, we could optimistically observe that anti-cancer-vaccines stand as an outstanding example of the successful implementation of modern biotechnology tools for the development of biologically sound therapeutics. In particular, vaccines against melanoma (the prototype model of tumor immunology in humans) can reproducibly induce cytotoxic T cell (CTL) responses exquisitely specific for cancer cells. This achievement trespasses the specificity of any other anti-cancer therapy. The skeptics, on the other end, might point out that immunization only rarely leads to cancer regression, labeling, therefore, this approach is ineffective. In our opinion this judgment stems from the naïve expectation that CTL induction is sufficient for an effective immune response. Here we propose that more needs to be understood about the mechanisms required for the induction of a therapeutically relevant immune response in humans. In particular, we will discuss the variables related to cancer heterogeneity, the weight of individual patients’ polymorphism(s), the role of the T cell activation and differentiation and, finally, the complex relationship between immune and cancer cells within the tumor microenvironment.