Figure 1.

Cancer immunity cycle. Immunogenic death of tumor cells leads to release of tumor-specific antigens (AG) that are captured by antigen presenting cells (APC) and after binding to major histocompatibility complex (MHC) class II are presented on their surface. The receptors CD4 dock to an MHC class II, activate the naive T helper (TH) cells followed by clonal selection of antigen-specific T cells, their proliferation, migration into the tumor site and differentiation into cytotoxic T-lymphocytes (CTL). CTL express receptors CD8, which dock to MHC class I. Finally, CTL recognize tumor-specific antigens and kill the tumor cells, which produces a further release of tumor antigens into the surrounding space and potentiates the immune response. Natural killer (NK) cells recognize tumor cells without the involvement of the MHC class I, making the response mediated very quick. AG, tumor-associated antigens; MHC I, major histocompatibility complex class I; MHC II, major histocompatibility complex class II; TH, T helper cell; NK, natural killer cell.