CTLA4 and melanoma: Studies in melanoma and prostate cancer patients documented a strong positive correlation between low levels of MDSCs and efficacy of the CBI antibody ipilimumab (anti-CTLA4) [7,8] and a lack of responsiveness to ipilimumab and the CBI antibody nivolumab (anti-PD-1) in melanoma patients with high levels of MDSCs [9,10,11].