Efficacy of filgrastim therapy for patients with progressive multifocal leukoencephalopathy: Two case reports.

Progressive multifocal leukoencephalopathy (PML) is a life-threatening central nervous system condition caused by reactivation of JC virus in individuals with immunosuppression. Although PML typically develops in patients with human immunodeficiency virus (HIV), cases in individuals without HIV have been increasing in recent years. Non-HIV-associated PML has a particularly poor prognosis, high mortality rates, and few therapeutic options. Here, we present the cases of two patients with non-HIV-, nondrug-associated PML who achieved good clinical outcomes after treatment with filgrastim (granulocyte colony-stimulating factor [G-CSF]). One patient had a diagnosis of Good syndrome, a rare primary immunodeficiency disease, whereas the other presented with lymphopenia and a mild decrease in CD4 T cells. After G-CSF administration, both patients showed decreases in CSF JC virus loads and improvements on magnetic resonance images. Given these findings, we propose that, by stimulating innate immunity and activating anti-JC viral immune surveillance, G-CSF may be useful as an immune-enhancing therapy for patients with non-HIV-associated PML.