Adoptive JC Virus-Specific T Lymphocytes for the Treatment of Progressive Multifocal Leukoencephalopathy: Experience from Two Italian Centers

Background: Progressive multifocal leukoencephalopathy (PML) is a rare but fatal disease caused by John Cunningham virus (JCV) in immunocompromised individuals, with no effective antiviral treatment currently available. This study aimed to evaluate the feasibility of adoptive JCV-specific T lymphocyte therapy in patients with PML. Methods: Nineteen patients meeting the 2013 consensus criteria for “definite PML” were included, and JCV-specific T lymphocytes expanded from autologous or allogeneic peripheral blood mononuclear cells (PBMCs) using JCV antigen-derived peptides were administered. Clinical outcomes were monitored through neuroimaging and biological markers. Results: The mean age at diagnosis was 56.5 years, with a mean time to treatment of three months. Patients received a median of two infusions. At 12 months, six patients (31.6%) survived, while 13 (68.4%) had died, primarily due to PML progression. Survivors had a higher median baseline Karnofsky performance scale (KPS) score (50% vs. 30%, p = 0.41) and a significantly shorter diagnosis delay. MRI assessment showed a reduced disease burden in survivors, and JCV-DNA copy numbers decreased overall. One case of immune reconstitution inflammatory syndrome (IRIS) was observed. Conclusions: Adoptive JCV-specific T lymphocytes may represent a safe therapeutic option for PML patients, and the MRI burden and JCV-DNA copy may serve as biomarkers for disease monitoring.