Association of prolonged survival in HLA-A2⁺ progressive multifocal leukoencephalopathy patients with a CTL response specific for a commonly recognized JC virus epitope

The role of JC virus (JCV)-specific CTL was explored in the immunopathogenesis of progressive multifocal leukoencephalopathy (PML). We identified a 9-aa epitope of the JCV capsid protein VP1, the VP1_p100 peptide ILMWEAVTL, which is recognized by CTL of HLA-A2⁺ HIV⁺/PML survivors. We then constructed an HLA-Az.ast;0201/VP1_p100 tetrameric complex that allowed us to assess by flow cytometry the PBMC of 13 PML patients and 11 control subjects for the presence of JCV-specific CTL. VP1_p100-specific CTL were detected by tetramer binding in VP1_p100-stimulated PBMC of five of seven (71%) PML survivors and zero of six PML progressors (p = 0.02). Two of three HIV⁺ patients with a leukoencephalopathy resembling PML, but with no virologic evidence of JCV infection, also had detectable VP1_p100-specific CTL in their PBMC. PBMC of eight HIV⁺ patients with other neurologic diseases and healthy control subjects had no detectable JCV-specific CTL. These data suggest that the JCV-specific cellular immune response may be important in the containment of PML, and the tetramer-staining assay may provide a useful prognostic tool in the clinical management of these patients.