CD4 and progressive multifocal leukoencephalopathy: To rule out that a short-term activation may have induced differentiation to TEM or TEMRA from less differentiated memory T cells, we sorted CD4+ and CD8+ stem cell memory T cells (TSCM), central memory T cells (TCM), and effector memory T cells (TEM) from AIDS-associated PML patients and MS patients on natalizumab (see Methods).