In this double-blind study involving 142 patients with metastatic melanoma who had not previously received treatment , we randomly assigned patients in a 2:1 ratio to receive ipilimumab ( 3 mg per kilogram of body weight ) combined with either nivolumab ( 1 mg per kilogram ) or placebo once every 3 weeks for four doses , followed by nivolumab ( 3 mg per kilogram ) or placebo every 2 weeks until the occurrence of disease progression or unacceptable toxic effects .