Thus, inhibition of Ptpn2 by the small-molecule PTP 9 sensitizes melanoma tumors to anti-PD-1 therapy in vivo, at least in part, by restoring the ability to respond to IFNγ, thereby increasing T-cell chemokine expression and recruitment of cytolytic T cells to the tumor microenvironment. The gene discussed is PDCD1; the disease is neoplasm.