Autoimmune hemolytic anemia induced by anti-PD-1 therapy in metastatic melanoma.

We report the occurrence of autoimmune hemolytic anemia in a patient receiving the anti-PD-1 monoclonal antibody, nivolumab, for metastatic melanoma in the presence of known red cell alloantibodies, despite having received prior ipilimumab without evidence of hemolysis. The patient had a history of multiple red cell alloantibodies and a positive direct antiglobulin test, identified at the time of a prior transfusion, which occurred before treatment with ipilimumab. The patient developed symptomatic warm autoimmune hemolytic anemia after four cycles of treatment with nivolumab. Clinical improvement was noted following cessation of the drug and treatment with corticosteroids. Given that there was no prior history of hemolysis, even during treatment with ipilimumab, we hypothesize that anti-PD-1 therapy disrupted peripheral tolerance, unmasking an underlying autoimmune predisposition.