IL10 and progressive multifocal leukoencephalopathy: In particular, it was observed that in patients treated with natalizumab, the magnitude and the quality of JCV-specific T-cell response did not change from the healthy patients, while in patients with natalizumab-associated PML, JCV-specific T cells were not measurable or JCV-specific T cells were dominated by IL-10 (human cytokine synthesis inhibitory factor) production, giving further evidence of the role of T-cell response in PML development [72].