Progressive multifocal leukoencephalopathy (PML) is a neurological disorder characterized by the destruction of myelin-producing cells responsible for protecting nerve cells in the brain and spinal cord. The disease is caused by the JC virus and is typically fatal. Over the past few years, the use of pembrolizumab has increased to strengthen the immunity in patients with PML. The objective of this study is to analyze the efficacy of pembrolizumab in the treatment of PML.

This study included a total of eight adult patients with PML and with different underlying predisposing conditions. Each participant was assigned to a 2 mg per kg BW dose of pembrolizumab every four to six weeks. The primary outcomes were the JC viral load and CD4+ and CD8+ activity against the JC virus. 

Pembrolizumab resulted in a down-regulation of PD-1 expression on lymphocytes and cerebrospinal fluid in all eight patients. Five patients showed clinical improvement or stabilization of PML with reduced JC viral load and an increase in in-vitro  CD4+ and CD8+ anti–JC virus activity.

The research concluded that pembrolizumab treatment for PML could reduce JC viral load and increase CD4+ and CD8+ activity against the JC virus. Besides, clinical improvements were also recorded in five of eight patients.