The impact of fingolimod on Treg function in brain ischaemia

Fingolimod has generally shown neuroprotective effects in stroke models. Here, we tested the hypothesis that fingolimod modulates T-cell cytokine production towards a regulatory phenotype. Second, we investigated how fingolimod altered the Treg suppressive function and the sensitivity of effector T cells to regulation. Mice that had underwent the permanent electrocoagulation of the left middle cerebral artery received saline or fingolimod (0.5 mg/kg) daily for 10-days post-ischaemia. Fingolimod improved neurobehavioural recovery compared to saline control and increased Treg frequency in the periphery and brain. Tregs from fingolimod-treated animals had a higher expression of CCR8. Fingolimod increased the frequencies of CD4⁺IL-10⁺, CD4⁺ IFN-γ⁺ and CD4⁺IL-10⁺IFN-γ⁺ cells in spleen and blood, and CD4⁺ IL-17⁺ cells in the spleen, with only minor effects on CD8⁺ T-cell cytokine production. Treg from post–ischaemic mice had reduced suppressive function compared to Treg from non-ischaemic mice. Fingolimod treatment rescued this function against saline-treated but not fingolimod-treated CD4⁺ effector T cells. In conclusion, fingolimod seems to improve the suppressive function of Treg post-stroke while also increasing the resistance of CD4⁺ effector cells to this suppression. Fingolimod's capacity to increase both effector and regulatory functions may explain the lack of consistent improvement in functional recovery in experimental brain ischaemia.