Experiments involving co-culture of Jurkat cells with HepG2 tumor cells showed that PD-1 expression on Jurkat cells increased after co-culture with cancer cells leading to cell cycle arrest of Jurkat cells, and blockade of PD-1 pathway by an anti-PD1 monoclonal antibody successfully restored T-cell function (66). The gene discussed is PDCD1; the disease is neoplasm.