CD34 and progressive multifocal leukoencephalopathy: Primary B lymphocytes and CD34+ hematopoietic progenitor cells in culture are susceptible to JCPyV infection [163,164], whereas CD34+ progenitors and B cells from PML patient spleen [82], bone marrow, blood [157,158,163,165,166,167,168], and brains [169] were positive for JCPyV DNA.