Using unstimulated peripheral blood mononuclear cells (PBMCs), isolated NK cells, NK cell lines, and lymphokine-activated killer cells (LAK cells), it was shown that the release of perforin/granzyme-containing granules, the secretion of IFN-γ and TNF-α, and the cytotoxic response against tumor cells assessed in vitro were markedly inhibited at low pH values, in the range of 5.8 to 7.0 [90–92]. The gene discussed is IFNG; the disease is neoplasm.