IFNB1 and metastatic melanoma: Because the anti-tumor effects of nivolumab are determined, at least in part, by the number of TILs and their expression of PD-1 [3], and because IFN-β increases the number of PD-1-expressing TILs at melanoma tumor cites, in vivo [10], we hypothesized that IFN-β could improve the efficacy of nivolumab for treatment of human metastatic melanoma.