Immune response to tumor cells and main mechanisms of action of anti-programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) and anti-cytotoxic T lymphocyte-associated protein-4 (CTLA-4). Tumor cells release antigens that are uptaken by antigen-presenting cells. These cells present tumoral antigens to naïve T-cells, thus activating them. The interaction between PD-1 in activated T-cells and PD-L1 in tumor cells can inhibit the immune response. CD80 on antigen-presenting cells can bind to CTLA-4 on activated T-cells and inhibit the immune response. Anti PD-1/PD-L1 and anti-CTLA4 monoclonal antibodies can bind to PD-1 in activated T-cells, PD-1 in tumor cells, or CTLA-4 in tumor cells, respectively, thus restoring the immune response.