Central Nervous System Uptake of Anti-CD8+ T Cell Minibodies in Multiple Sclerosis and Progressive Multifocal Leukoencephalopathy

Background: Multiple sclerosis (MS) and progressive multifocal leukoencephalopathy (PML) are disorders that affect the central nervous system (CNS). The CNS includes the brain, spinal cord, and optic nerves. Both diseases can cause muscle weakness and impair vision, speech, and coordination. Researchers are working to better understand how MS and PML affect the CNS. Objective: To test whether an experimental radioactive tracer (minibody) can help positron emission tomography (PET) scans detect certain immune cells in the CNS of people with MS and PML. Eligibility: People aged 18 years and older with MS, other neuroinflammatory diseases with BBB leakage, or PML. Design: Participants will come to the clinic for at least 3 visits over 4 to 6 weeks. Participants will undergo testing. They will have a physical and neurological exam. They will have blood tests and tests of their heart function. They will have a magnetic resonance imaging (MRI) scan of the brain. They may have a spinal tap: Their lower back will be numbed, and a needle will be inserted between the bones of the spine to withdraw fluid from around the spinal cord. Minibody is given through a tube with a needle placed in a vein in the arm. This takes 5 to 10 minutes. Participants will have heart function tests before and after receiving the minibody. Participants may have a PET scan on the day of the Minibody and will return the next day for another PET scan. They will lie on a table that moves through a doughnut-shaped machine. This scan will take about 1 hour. Participants with PML may opt to repeat the minibody infusion and the PET scan within 6 months.