Patients with detectable virus-specific T cells before checkpoint inhibitor therapy in PML demonstrated better survival rates and functional recovery than those without.

Question Are pretreatment JC virus-and/or BK virus-specific T cells in the blood associated with the efficacy of immune checkpoint inhibitors (ICIs) in progressive multifocal leukoencephalopathy (PML)?

Findings In this cohort study of 111 patients with PML treated with ICIs, those with detectable virus-specific T cells (n = 21) had significantly higher response rates and longer survival than both T cell–negative patients (n = 22) and those with unknown status (n = 68).