CD4 and progressive multifocal leukoencephalopathy: In a recent review from Cortese et al. [17], the authors concluded that biomarkers in PML can be divided into three categories: those referring to tissue destruction (MRI lesion burden, neurofilament light chains), to the virological burden (mainly JCV-DNA copy number), and to immune reconstitution (contrast-enhancing lesions, CD4+ and CD8+ counts, especially in HIV-positive patients).