Changes in Th17 and regulatory T cells after fingolimod initiation to treat multiple sclerosis

Fingolimod has demonstrated efficacy in patients with multiple sclerosis (MS), and patients become gradually lymphopenic after a few days of treatment, with selective reductions in CD4+ subsets. We observed an increase in the frequencies of circulating regulatory T cells after fingolimod administration. However, we also found that half of patients had increased proportion of circulating Th17 cells in CD4+ T cells after treatment (including a patient with MS relapses), whereas the others showed lower frequencies of Th17 cells, indicating some variability among patients. Further studies may confirm if slower reduction of circulating Th17 cells following fingolimod initiation predisposes to relapses.