We have recently reported that lowering the pH to values that are frequently detected in tumors causes reversible anergy in both human and mouse CD8⁺ T lymphocytes in vitro. The same occurs in vivo, in the tumor microenvironment and the administration of proton pump inhibitors, which buffer tumor acidity, can revert T-cell anergy and increase the efficacy of immunotherapy.

https://www.ncbi.nlm.nih.gov/pubmed/23483769