CTLA4 and melanoma: This is likely the case with ipilimumab, an IgG1 isotype antibody, since it has been reported that its ability to engage FcγRIIIa can lead to the cytotoxic killing of CTLA-4-expressing Tregs by effector cells such as macrophages and NK cells.81 In contrast, one contributor to immune evasion and melanoma progression may be the signaling through inhibitory FcRs on TAMs.