Further studies could be valuable to assess CCR5 chemokines CCL3, CCL4, and CCL5 in the periphery and in the CSF in the context of classical PML and in inflammatory PML, as well as the effect of CCR5 blockade on the proportion and number of CCR5-expressing T cells in the CSF and in brain tissue. The gene discussed is CCL4; the disease is progressive multifocal leukoencephalopathy.