In recent years, the need for new therapies against multidrug-resistant tumors and the secondary effects of current therapies, e.g. chemotherapy, have led to the study and the development of better ‘targeted’ therapies with less deleterious side effects for patients. Therefore, enhancing the ability of the immune system to detect and remove pathological cells through recognition of tumor or different expression patterns of the target cells is a crucial step to develop better therapies. PD-1 is an inhibitory receptor that suppresses T cell responses independent of CD28 but dependent of its ligands PD-L1 and PD-L2, which are abundantly expressed by several types of tumor cells. This study, together with {1,2}, describes the development of antibodies against PD-1 and PD-L1/2 with the aim of finding different anti-tumor therapies. This Recommendation is of an article referenced in an F1000 Faculty Review also written by Alvaro Ortega-Carrion and Miguel Vicente-Manzanares.