This suggests higher PD-1 expression in cluster C than in cluster D. Jacquelot et al. have recently reported an association between a greater baseline level of PD-1 (>20%) on circulating CD4+ T cells from melanoma patients and the likelihood to respond to an ex vivo metastatic lymph nodes assay using anti-PD1 monoclonal antibody [24]. This evidence concerns the gene CD4 and melanoma.