JC virus-specific immune responses in human immunodeficiency virus type 1 patients with progressive multifocal leukoencephalopathy. gan Khanna, N, Wolbers, M, Mueller, N, Garzoni, C, Du Pasquier, R, Fux, C, Vernazza, P, Bernasconi, E, Viscidi, R, Battegay, M, Hirsch, H