Pembrolizumab as a treatment for PML? Waiting for Godot.

Progressive multifocal leukoencephalopathy (PML) is an infrequent but severe disease of the brain. In the setting of immunosuppression, the polyomavirus JC (JCV) may reactivate, migrate to the brain, infect oligodendrocytes, and to a lesser extent astrocytes, and cause demyelinating lesions. As there are currently no available anti-JCV therapy, the only treatment consists of restoring immunity. Whereas restoring immunity is feasible in patients with AIDS-PML (by giving antiretroviral therapy) or in natalizumab-treated patients with MS (by stopping administration of natalizumab), achieving this in patients with hemopathies or with an intrinsically defective immune response is less straightforward. Consequently, the prognosis is particularly grim in the latter patients.