In a separate letter, authors describe a case of a patient with progressive multifocal leukoencephalopathy (PML) who had clinical stabilisation and no progression as assessed on magnetic resonance imaging (MRI) as a result of treatment with pembrolizumab. This case report supports the concept that blocking the pathway of programmed death 1 (PD-1) or its ligands (PD-L1 and PD-L2) can ameliorate JCV infection. The durability of PD-1 blockade and the use of ongoing infusions in patients with PML are still unclear.
A second letter describes a case of a 60-year-old woman with no history of immunosuppression or infection who presented with progressive temporospatial disorientation, speech disturbances, apraxia, and central facial palsy on the right side. A diagnosis of idiopathic primary immunodeficiency disease was made following detailed investigations (CSF had 200,000 copies of JCV per mL) and treatment with nivolumab produced a favourable outcome.
An editorial discussing these reports questions “Do pembrolizumab and nivolumab fit the bill for treatment of PML?”. The authors conclude that the current reports are encouraging but suggest that the presence of JC virus–specific T cells in the blood is a prerequisite for their use. A controlled trial may be needed to determine whether immune checkpoint inhibitors are indeed able to keep JC virus in check in patients with PML.