Heart and lung transplant: 1.24 per 1,000 post-transplant patients yearsRare in other SOT and HCTRisk factors for JCPyV-PML: CD4 + lymphocytopenia, older age (rare in patients less than 21 years of age), alloCT, receipt of two or more IS agents; occurs at median of 11 months (HCT) to 27 months (SOT)CNS disease is rare. The gene discussed is CD4; the disease is progressive multifocal leukoencephalopathy.