Single-Dose Pembrolizumab Treatment for Progressive Multifocal Leukoencephalopathy.

Progressive multifocal leukoencephalopathy (PML) is a rare but emerging demyelinating neurologic infection of the CNS caused by reactivation of the John Cunningham (JC) virus. Several immunocompromised populations are susceptible for PML, for example, those with hematologic malignancy, HIV infection, transplant recipients, and specific disease-modifying therapies. For the total PML population, 1and 5-year survival rates have been estimated to be 30% and 10%, respectively. Themost crucial factor in the chances of survival depends on whether immune function can be restored. Pembrolizumab is amonoclonal antibody that blocks programmed cell death protein-1 on the surface of the T cell, allowing T cells to be reactivated and to facilitate the clearance of the virus. Pembrolizumab treatment of 8 patients with PML led to decreased CSF viral load in all patients and stabilization of clinical deterioration or improvement in 5 patients. Subsequently, 2 patients with PML were reported without clinical improvement after pembrolizumab treatment. In the literature, 11 patients with PML treated with pembrolizumab have been described, of whom 6 had a favorable outcome.