Daud et al. showed significant correlation between CD8 T cells expressing high levels of CTLA-4 and PD-1 with clinical response and progression free survival in freshly isolated metastatic melanoma samples from 40 patients prior to treatment with anti-PD-1, suggesting that relative abundance of this T cell population may predict treatment response (Daud et al. 2016). Here, CTLA4 is linked to metastatic melanoma.