In order to determine whether MHC-II expression on melanoma tumours is associated with clinical response to PD-1/PD-L1-targeted therapy, we obtained archival pre-treatment biopsy or resection specimens from 30 patients treated with anti-PD-1 (nivolumab, pembrolizumab) or anti-PD-L1 (MPDL3280A; n=2). The gene discussed is CD274; the disease is melanoma.