To investigate the dynamics of immune cells recovery after treatment discontinuation of fingolimod in real-life clinical practice, we analyzed the course of lymphocyte reconstitution and its potential influencing factors in patients with multiple sclerosis (MS).

We analyzed leukocyte, lymphocyte, and granulocyte counts of 58 patients at 3, 6, and 12 months after fingolimod cessation and the following parameters as potential risk factors for a prolonged lymphopenia up to 12 months: age; sex; Expanded Disability Status Scale, and disease duration at the time of fingolimod start; type and number of previous immunomodulatory treatments; fingolimod treatment duration; lymphocyte count at baseline before fingolimod, at fingolimod stop, and at the time of therapy switch; time interval between fingolimod cessation and new treatment initiation; type of the follow-up immunomodulatory treatment; and corticosteroid administration after fingolimod cessation.

All patients showed a drop of the lymphocyte count under fingolimod with no relevant leukopenia or neutropenia. One year after discontinuation, still 22% of the patients were lymphopenic and 54% of them did not reach 80% of the baseline lymphocyte value. Low lymphocyte counts before fingolimod start, under fingolimod, and at therapy switch, successive treatment with rituximab, and pretreatment with mitoxantrone were significantly associated with a prolonged immune cell recovery.

Prolonged lymphopenia after fingolimod cessation exists in a subgroup of patients with MS and should be considered in clinical practice, particularly when changing treatment regimens.