PDCD1 and cancer: Understanding and studying the tumor microenvironment has allowed for the development of new therapeutic strategies against cancer, such as immune system stimulators (IL-2 and INF-α), therapeutic vaccines, adoptive cell therapy, use of antibodies (anti-CTLA-4, anti-PD1, and anti-PD-L1) that trigger anticancer T responses, use of oncolytic virus therapies, and the combined use of these strategies as antagonistic models for cancer development [90,91,92,93].