Immunosuppression increases JC polyomavirus large T antigen DNA load in the brains of patients without progressive multifocal leukoencephalopathy.

The relationship between latent JC polyomavirus (JCV) infection and progressive multifocal leukoencephalopathy (PML) remains unclear. In this study, JCV DNA was quantified by real-time polymerase chain reaction (qPCR) in brain and kidney tissue from patients without PML. Immunosuppressed patients had significantly higher JCV DNA levels in brain, compared with immunocompetent patients (P = .001). An inverse relationship was observed between CD4(+) T-cell counts and qPCR-determined brain JCV load among patients with HIV infection (r(2) = -0.9; P = .01; n = 7). Higher kidney JCV DNA load was strongly associated with higher brain JCV DNA load (Spearman ρ = 0.65; P = .004; n = 18). These findings highlight the importance of latent JVC brain infection to the pathogenesis of PML.