Background: Progressive Multifocal Leukoencephalopathy (PML) is a brain infection in people with a weakened immune system. Researchers think polyoma virus specific T cells (PyVST) therapy can treat PML. The PyVST cells are made from blood cells of a healthy relative. They are grown in a lab to expand the virus-killing cells, then given to the person with PML. Objective: To test whether PyVST safely treats PML. Eligibility: * Adults ages 18 and older with PML * Healthy adults ages 18 and older who have: * Been screened under protocol 97-H-0041 * A sibling, parent, or child with PML and matching cells Design: * Participants will be screened with: * Medical history * Physical exam * Blood and urine tests * PML participants will also be screened with: * Cerebrospinal fluid removed by needle in the back. * MRI: A dye is injected in a vein. They lie on a table that slides into a cylinder. * Questionnaires Healthy participants will have apheresis: Blood flows through a needle in one arm into machine that separates blood cells needed for donation. The rest of the blood is returned by needle to the other arm. Some participants may have a central line placed in a vein instead. They can have apheresis up to 3 times, at least 28 days apart. Participants with PML will receive the PyVST cells by needle in the arm. They will stay in the hospital 1 week. They can do this up to 3 times, at least 28 days apart. After each infusion, they will have weekly visits for 1 month. Then they will have 4 visits over 1 year. Visits include repeats of screening tests.
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Characterization of the safety and feasibility of PyVST infusion for the treatment of PML based on development of Treatment Limiting Toxicity
Timeframe: ongoing