CD4 and progressive multifocal leukoencephalopathy: The transition from a negative (active) to a positive (acute remission) JCV-OII for PML #3 coupled with the positive JCV-OII values for those with chronic PML (Figure 2D; Table 2) suggests that the development of CD4+ T cell mediated immunity to JCV may be important for prolonged survival in patients with PML, however, it will be necessary to do longer term follow-up to make this determination.