BACKGROUND An improvement in overall survival among patients with metastatic melanoma has been an elusive goal. In this phase 3 study, ipilimumab — which blocks cytotoxic T-lymphocyte–associated antigen 4 to potentiate an antitumor T-cell response — administered with or without a glycoprotein 100 (gp100) peptide vaccine was compared with gp100 alone in patients with previously treated metastatic melanoma. METHODS A total of 676 HLA-A⋆0201–positive patients with unresectable stage III or IV melanoma, whose disease had progressed while they were receiving therapy for metastatic disease, were randomly assigned, in a 3:1:1 ratio, to receive ipilimumab plus gp100 (403 patients), ipilimumab alone (137), or gp100 alone (136). Ipilimumab, at a dose of 3 mg per kilogram of body weight, was administered with or without gp100 every 3 weeks for up to four treatments (induction). Eligible patients could receive reinduction therapy. The primary end point was overall survival. RESULTS The median overall survival was 10.0 months among patients receiving ipilimumab plus gp100, as compared with 6.4 months among patients receiving gp100 alone (hazard ratio for death, 0.68; P<0.001). The median overall survival with ipilimumab alone was 10.1 months (hazard ratio for death in the comparison with gp100 alone, 0.66; P = 0.003). No difference in overall survival was detected between the ipilimumab groups (hazard ratio with ipilimumab plus gp100, 1.04; P = 0.76). Grade 3 or 4 immune-related adverse events occurred in 10 to 15% of patients treated with ipilimumab and in 3% treated with gp100 alone. There were 14 deaths related to the study drugs (2.1%), and 7 were associated with immune-related adverse events. CONCLUSIONS Ipilimumab, with or without a gp100 peptide vaccine, as compared with gp100 alone, improved overall survival in patients with previously treated metastatic melanoma. Adverse events can be severe, long-lasting, or both, but most are reversible with appropriate treatment. (Funded by Medarex and Bristol-Myers Squibb; ClinicalTrials.gov number, NCT00094653.)

Defective dendritic cell (DC) function caused by abnormal differentiation of these cells is an important mechanism of tumor escape from immune system control. Previously, we have demonstrated that the number and function of DC were dramatically reduced in cancer patients. This effect was closely associated with accumulation of immature cells (ImC) in peripheral blood. In this study, we investigated the nature and functional role of those ImC. Using flow cytometry, electron microscopy, colony formation assays, and cell differentiation in the presence of different cell growth factors, we have determined that the population of ImC is composed of a small percentage (&lt;2%) of hemopoietic progenitor cells, with all other cells being represented by MHC class I-positive myeloid cells. About one-third of ImC were immature macrophages and DC, and the remaining cells were immature myeloid cells at earlier stages of differentiation. These cells were differentiated into mature DC in the presence of 1 μM all-trans-retinoic acid. Removal of ImC from DC fractions completely restored the ability of the DC to stimulate allogeneic T cells. In two different experimental systems ImC inhibited Ag-specific T cell responses. Thus, immature myeloid cells generated in large numbers in cancer patients are able to directly inhibit Ag-specific T cell responses. This may represent a new mechanism of immune suppression in cancer and may suggest a new approach to cancer treatment.

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To our knowledge, this is the largest series of patients with preexisting autoimmune disease treated with immune checkpoint inhibitors. Ipilimumab was clinically active and was associated with exacerbations of autoimmune disease and conventional ipilimumab-induced irAEs that were readily manageable with standard therapies when started in a timely fashion. Ipilimumab therapy may be considered in this setting with vigilant clinical monitoring.