Unexpected Toxicities When Nivolumab Was Given as Maintenance Therapy following Allogeneic Stem Cell Transplantation.

Treatment options are limited for patients with hematologic malignancies who relapse after allogeneic stem cell transplantation (allo-SCT). We conducted a pilot study to assess the tolerability and efficacy of low-dose nivolumab, a PD-1 inhibitor, as maintenance therapy after allo-SCT. Of the 4 patients enrolled in the study, all rapidly developed immune-related adverse events (irAEs); 2 patients experienced serious adverse events, including grade 4 neutropenia and grade 3 autoimmune encephalopathy. As a result of these unexpected severe toxicities, the study was closed to further enrollment. Even at low doses, nivolumab maintenance in the post allo-SCT setting can cause serious irAEs beyond graft-versus-host disease, and further studies of dosage and timing after allo-SCT are needed.