Ipilimumab-triggered ADCC is dependent on the expression of CTLA-4 on melanoma cells. PBMC (A, n = 6), IL-2-activated NK (B, n = 4) and Vδ2+T cell populations (C, n = 3) were analyzed for ADCC activity using the melanoma cell lines: MECO (left), METR (middle) or FO-1 (right). Experiments were performed at the indicated E:T ratios without (none) or with anti-CTLA-4 Ipilimumab Ab or anti-CD20 Rituximab Ab. Results are expressed as % of 51Cr specific release and are the mean ± SD of results obtained with different effectors. Inserts in the first row of histograms show the reactivity of Ipilimumab (MRFI) with the indicated cell lines. Reactivity was analyzed by indirect immunofluorescence on a cytofluorimeter. Open histograms or filled histograms represent staining with either anti-CTLA-4 Ipilimumab Ab or isotype control Ab respectively.