PDCD1 and cancer: The focus of this study is on the resistance to cancer elimination by immune checkpoints Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), Programmed cell death protein 1 (PD-1), and Programmed death-ligand 1 (PD-L1) and how their blockade by immune checkpoint inhibitors can lead to a range of patient responses through variations in specific physiological parameters, such as those described above (i.e., numbers of T cell clones, tumor size and antigen strength), encoded in a mechanistic framework.