Nivolumab for Treatment of Progressive Multifocal Leukoencephalopathy in Sézary Syndrome.

Progressive multifocal leukoencephalopathy (PML) is a rare but severe opportunistic CNS infection caused by JC polyomavirus in immunosuppressed patients. Immune checkpoint blockade stimulates immune function and has been suggested to reinvigorate viral clearance in PML patients by expanding JCV-specific T cells1 . Among the first 13 published PML patients treated with programmed cell death 1 inhibitors (PD1I) 8 showed a mild to marked treatment response2-7 . The underlying conditions ranged from chronic lymphocytic leukemia, AIDS, Non-Hodgkin lymphoma, idiopathic lymphopenia, variable immune deficiency, Hodgkin lymphoma, B-cell lymphoma to primary and combined immunodeficiency. Here, we present a patient with Sézary syndrome (SS) who developed PML and did not benefit from treatment with nivolumab.