Fig 1.

Detection of JCV-specific effector memory T cells (TEM) in blood of two natalizumab-treated patients with PML. In panels A and B, PBMC from one patient who developed PML following natalizumab treatment (39 infusions) were activated with purified JC virus overnight and then tested for intracellular IFN-γ by flow cytometry in the CD4 and CD8 T-cell subsets (A and B, respectively). CCR7 and CD45RA expression on IFN-γ-positive and -negative cells is also shown for CD4 T cells (A) and CD8 T cells (B). In panel C, PBMC from 2 patients who developed PML on natalizumab (patient 1 and patient 2 received 39 and 24 infusions, respectively) were activated overnight with purified JC virus and/or with a pool of VP1 peptides prior to IFN-γ ELISPOT. The numbers of IFN-γ spots per 0.25 × 10⁶ PBMC after overnight activation with purified JCV and JCV peptide pools were 54 and 21, respectively (untreated well, 0 spots) in patient 1. In patient 2, purified JCV yielded 15 spots (untreated well, 0 spots).