Low frequencies of central memory CD4 T cells in progressive multifocal leukoencephalopathy

OBJECTIVES: To assess alterations in the composition of peripheral immune cells in acute progressive multifocal leukoencephalopathy (PML). METHODS: Fresh blood samples from 5 patients with acute PML and 10 healthy controls were analyzed by flow cytometry for naive, central memory and effector memory CD4 and CD8 T cells, B lymphocytes, plasma cells, memory B cells, plasma blasts, and natural killer (NK) cells. The frequency of central memory CD4 T cells was determined longitudinally during the course of PML in 2 patients. RESULTS: The frequencies of naive, central memory and effector memory CD8 T cells, B cells, plasma cells, and NK cells were not altered in patients with PML. In contrast, the frequencies of naive CD4 T cells (p = 0.04) and central memory CD4 T cells (p < 0.00001) were reduced and the frequencies of effector memory CD4 T cells were increased (p = 0.01). Longitudinal analysis showed that this pattern was preserved in a patient with fatal PML outcome and restored in one patient who recovered from PML. CONCLUSIONS: These data indicate that PML is associated with reduced frequencies of peripheral central memory helper T cells but not with alterations in the frequencies of cytotoxic T cell populations, B lymphocytes, plasma cells, or NK cells.