However, supporting the hypothesis of PD-1 as a marker of hypofunction, but not necessarily of terminal exhaustion, one study demonstrated that mesothelin/BBζ T cells that had high PD-1 expression and a hypofunctional phenotype in an vivo human mesothelioma model recovered the ability to produce cytokines and had lower PD-1 expression after 24 h out of the tumor (126). The gene discussed is PDCD1; the disease is mesothelioma.