CD4 and progressive multifocal leukoencephalopathy: In conclusion, although the pathomechanisms of PML remain elusive, our data indicate that bioenergetic parameters relating to CD4+-mediated immunity may assist in neuroimmunological disease risk stratification and monitoring under mAb-immunotherapy, and may be a more sensitive measure than the CD4+ cell count, that is the only suggested measure of immunocompetence under natalizumab therapy to date [40].