The resolution of PML symptoms correlates with immunological recovery, as evidenced by normalization of T-CD4 + lymphocytes count (690/mm3) and a marked increase in T-CD8 + lymphocytes count (4200/mm3), which led to a rebound inflammatory reaction against brain infection evidenced by MRI findings which, in turn, resulted in viral clearance. This evidence concerns the gene CD4 and progressive multifocal leukoencephalopathy.