Clearance of JC polyomavirus from cerebrospinal fluid following treatment with interleukin-2 and pembrolizumab in an individual with progressive multifocal leukoencephalopathy and no underlying immune deficiency syndrome

A 71-year-old Caucasian man presented with dysarthria and fluctuating hypesthesia of the right upper limb in early 2019. Brain MRI demonstrated T2/FLAIR hyperintense lesions in the left parietal cortical grey matter and adjacent white matter compatible with embolic stroke of undetermined source. Eight weeks later symptoms had further progressed with loss of adequate communication, disturbance of fine motor skills, ataxia and neuropsychiatric symptoms. Widespread disease on brain MRI and the detection of JC polyomavirus (JCPyV) DNA from cerebrospinal fluid (CSF) confirmed the diagnosis of progressive multifocal leukoencephalopathy (PML). Bone marrow biopsy revealed normal findings, and no underlying cause of reduced immunocompetence was identified. Despite rehabilitation, treatment with mirtazapine, and two cycles of interleukin-2 (IL-2, 7 x 2 mio IE s.c.) administered two weeks apart, symptoms and MRI lesions further progressed, with complete immobility and severe dysphagia