According to this hypothesis, a recent study [37] of PML in an NZT-treated MS patient found lower numbers of DCs and CD4+ T cells in the cerebral perivascular spaces than in brain tissue from control patients with non-neurological diseases, patients with MS not treated with NTZ, and patients with PML not associated with NTZ therapy. This evidence concerns the gene CD4 and progressive multifocal leukoencephalopathy.