Literature Review

Can immune checkpoint inhibitors treat PML?



Treatment with pembrolizumab or nivolumab may benefit patients with progressive multifocal leukoencephalopathy (PML), investigators reported in the New England Journal of Medicine.

Three research teams described 10 cases in which patients with PML received pembrolizumab or nivolumab.

In one study, researchers administered pembrolizumab to eight adults with PML. Five patients had clinical improvement or stabilization, whereas 3 patients did not. Among the patients with clinical improvement, treatment led to reduced JC viral load in cerebrospinal fluid (CSF) and increased CD4+ and CD8+ anti–JC virus activity in vitro. Among patients without clinical improvement, treatment did not meaningfully change viral load or antiviral cellular immune response.

In a separate letter, researchers in Germany described an additional patient with PML who had clinical stabilization and no disease progression on MRI after treatment with pembrolizumab.

In another letter, researchers in France described a patient with PML whose condition improved after treatment with nivolumab.

“Do pembrolizumab and nivolumab fit the bill for treatment of PML? 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,” said Igor J. Koralnik, MD, of the department of neurological sciences at Rush University Medical Center in Chicago, in an accompanying editorial. “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.”

Reinvigorating T cells

Both monoclonal antibodies target programmed cell death protein 1 (PD-1), which inhibits T-cell proliferation and cytokine production when it binds its associated ligand, Dr. Koralnik said. Pembrolizumab and nivolumab block this inhibition and have been used to spur T-cell activity against tumors in patients with cancer.

PML, an often fatal brain infection caused by the JC virus in patients with immunosuppression, has no specific treatment. Management hinges on “recovery of the immune system, either by treating the underlying cause of immunosuppression or by discontinuing the use of immunosuppressive medications,” said Dr. Koralnik.


Prior studies have found that PD-1 expression is elevated on T lymphocytes of patients with PML. To determine whether PD-1 blockade with pembrolizumab reinvigorates anti–JC virus immune activity in patients with PML, Irene Cortese, MD, of the National Institutes of Health’s Neuroimmunology Clinic and her research colleagues administered pembrolizumab at a dose of 2 mg/kg of body weight every 4-6 weeks to eight adults with PML. The patients received 1-3 doses, and each patient had a different underlying condition.

In all patients, treatment induced down-regulation of PD-1 expression on lymphocytes in CSF and peripheral blood, and five of the eight patients had clinical stabilization or improvement. Of the other three patients who did not improve, one had stabilized prior to treatment and remained stable. The other two patients died from PML.

Additional reports

Separately, Sebastian Rauer, MD, of Albert Ludwigs University in Freiburg, Germany, and his colleagues reported that a patient with PML whose symptoms culminated in mutism in February 2018 began speaking again after receiving five infusions of pembrolizumab over 10 weeks. “In addition, the size and number of lesions on MRI decreased, and JCV was no longer detectable in CSF,” Dr. Rauer and his colleagues wrote. “The patient has remained stable as of the end of March 2019, with persistent but abating psychomotor slowing, aphasia, and disorientation.”


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