Natural killer (NK) cells of the innate immune system can profoundly impact the development of adaptive immune responses. Inflammatory and autoimmune responses in anatomical locations such as the central nervous system (CNS) differ substantially from those found in peripheral organs. We show in a mouse model of multiple sclerosis that NK cell enrichment results in disease amelioration, whereas selective blockade of NK cell homing to the CNS results in disease exacerbation. Importantly, the effects of NK cells on CNS pathology were dependent on the activity of CNS-resident, but not peripheral, NK cells. This activity of CNS-resident NK cells involved interactions with microglia and suppression of myelin-reactive Th17 cells. Our studies suggest an organ-specific activity of NK cells on the magnitude of CNS inflammation, providing potential new targets for therapeutic intervention.

The objective of this study is to characterize the timing and extent of radiologic MS disease recurrence during the 24-week natalizumab treatment interruption period in RESTORE. RESTORE was a randomized, partially placebo-controlled exploratory study. Natalizumab-treated patients with no gadolinium-enhancing (Gd+) lesions at screening (n = 175) were randomized 1:1:2 to continue natalizumab (n = 45), switch to placebo (n = 42), or switch to other therapies (n = 88) for 24 weeks. MRI assessments were performed every 4 weeks. Predictors of increased numbers of Gd+ lesions during natalizumab treatment interruption were evaluated. The numbers of Gd+ lesions were compared with retrospectively collected pre-natalizumab MRI reports and data from placebo-treated patients from two historical randomized clinical trials. Gd+ lesions were detected in 0 % (0/45) of natalizumab patients, 61 % (25/41) of placebo patients, and 48 % (39/81) of other-therapies patients during the randomized treatment period. Gd+ lesions were detected starting at week 12; most were observed at week 16 or later. Thirteen percent (14/107) of patients had >5 Gd+ lesions on ≥1 (of 6) scans during the randomized treatment period versus 7 % (7/107) of patients pre-natalizumab (based on medical record of a single scan). Younger patients and those with more Gd+ lesions pre-natalizumab were more likely to have increased MRI activity. Distribution of total and persistent Gd+ lesions in RESTORE patients was similar to placebo-treated historical control patients. In most patients, recurring radiological disease activity during natalizumab interruption did not exceed pre-natalizumab levels or levels seen in historical control patients.