Ipilimumab, Nivolumab and Pembrolizumab are human or humanized monoclonal antibodies (mAb) that target CTLA-4 or PD-1, respectively, and interfere with inhibitory signals delivered by these receptors to the T cell. The CTLA-4-directed mAb Ipilimumab has been approved as first- and second-line therapy for patients with malignant melanoma and showed promising results in terms of overall survival [6, review in 7]. Combination therapies including Ipilimumab and anti-PD-1 [8–10] or other mAbs  even proved to be superior to treatment with a single mAb.