Progressive Multifocal Leukoencephalopathy

Background: Progressive multifocal leukoencephalopathy (PML) is a rare and often fatal brain infection caused by the JC virus. The JC virus is common. More than half of adults have been exposed to it. Most people do not get sick from the JC virus, but in people with weakened immune systems, it can cause PML. Brincidofovir (BCV) is an antiviral drug approved to treat smallpox. Researchers want to know if it can help people with PML. Objective: To test BCV in people with PML. Eligibility: People aged 18 years or older with PML. Design: Participants will be screened. They will have a physical exam with blood tests. They will have an imaging scan of the brain with contrast dye. They will have a lumbar puncture (spinal tap): A thin needle will be inserted into their lower back to draw out a sample of the fluid around their spinal cord. BCV will be given through a tube attached to a needle inserted into a vein. Participants will receive the drug 2 times a week for 4 weeks (this is 1 cycle). If the drug is helping them, they may have up to 3 drug cycles (12 weeks). Imaging scans, spinal taps, and other tests will be repeated after every 4 weeks of treatment. Participants will have 6 follow-up visits in 1 year after treatment ends. The imaging scan, spinal tap, and other tests will be repeated at each visit.

Background: \- Progressive multifocal leukoencephalopathy (PML) is a severe viral infection of the brain. It is caused by JC virus. Many people have this virus in their bodies all their life, but it is usually kept in check by their immune system. If the immune system does not work right because of a disease or medication, the virus becomes active and can damage cells in the brain. Not much is known about PML or how it affects the immune system. Researchers want to study people with PML to better understand the natural history of the disease. Objectives: \- To study the natural history of PML. Eligibility: \- Individuals at least 2 years of age who have PML. Design: * Participants will be screened with a physical exam, medical history, and imaging studies. * Participants will have several visits to the National Institutes of Health Clinical Center. There will be an initial visit, monthly visits for the next 6 months, a 12-month visit, and possible visits afterward. * At the initial visit, participants will give blood, urine, and spinal fluid samples. They will also have neurological tests and imaging studies of the brain. * For the next five visits, participants will give blood and urine samples. They will also have neurological tests and imaging studies of the brain. * The 6-month and 12-month visits will repeat the tests from the initial visit. * Other optional procedures include bone marrow samples and skin biopsies. Additional blood tests and imaging studies may be performed. * Treatment will not be provided as part of this study.

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.

This research team intends to conduct a real-world cohort study of chronic CNS viral infections represented by PML, to evaluate whether administration of immune checkpoint inhibitors improves long-term outcomes in this patient population.Patients with prior follow-up will be enrolled into a retrospective/prospective ambidirectional cohort, and newly diagnosed patients will be enrolled into a prospective cohort.

This study aims to assess the efficacy and safety of pembrolizumab in immunocompromised patients with progressive multifocal leukoencephalopathy (PML). This phase II, multicenter, single-arm study includes patients with an underlying cause of immunosuppression hardly reversible, i.e. not the patients with HIV nor those receiving biologics for chronic inflammatory diseases. Patients will receive intravenous pembrolizumab (2 mg/kg, maximum 200 mg) at month 0, 1 and 2 (total of three doses). The primary endpoint will be achieving at least one negative result of JCV viral load in cerebrospinal fluid (CSF) within the M0 to M3 period.