In cord blood derived HSPC-generated humanized mouse model, PD-1 blocking (using nivolumab) inhibited the growth of MDAMB-231 tumor cells and CRC172 tumor cells by enhancing anti-tumor T cell response, increasing GrB+ or IFNγ+ CD8+ cells in tumors and reducing frequency of Treg and myeloid cells. The gene discussed is GZMB; the disease is neoplasm.