Interestingly, targeting tumor acidosis has also shown to increase the effectiveness of checkpoint inhibitors (antibodies directed to programmed cell death protein 1 (PD1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)) [120, 122] that have recently demonstrated tremendous potential for the treatment of a variety of solid tumors [136]. Here, PDCD1 is linked to neoplasm.