CD8A and progressive multifocal leukoencephalopathy: - Oligoclonal TCR repertoire in CSF of treated patients (spectratyping analysis (98); possible connection with impaired CNS immuno surveillance and higher risk of PML;- Persistence of clones, especially memory CD8+, in peripheral blood of RRMS afer 24 months of treatment (16);- Broader TCR sequence similarity architecture in peripheral blood compared to one-shot treatment (AHSCT) after 24 months of natalizumab (16).