Is antibody titer useful to verify the immunization after VZV Vaccine in MS patients treated with Fingolimod? A case series

•Patients given VZV vaccine may have loss of serum VZV antibody on subsequent treatment with fingolimod.•Vaccinated patients may still have T cell-mediated immunity to VZV but that is not routinely tested.•Reduction of B cells and immunoglobulin could interfere with vaccine antibodies titer. : Fingolimod (FTY720, Gilenya) is a second line therapy to treat relapsing MS not responding to first-line treatments and/or with a high disease activity (according to Italian Regulatory authorities). Before starting Fingolimod, patients’ immunity to varicella zoster virus (VZV) needs to be assessed and seronegative patients vaccinated. To test susceptibility and response, IgG antibodies are tested after immunization. Since Fingolimod determines a reduction of circulating B lymphocytes and immunoglobulins, we aimed at describing the trend of VZV antibodies in seronegative vaccinated patients with MS before and after treatment. : A total of 23 patients vaccinated for VZV before starting Fingolimod treatment, were recruited in this observational retrospective study involving five MS Centers in Campania (Italy). Of these, 12 patients were excluded for missing data. Patients received two doses of Varivax® Vaccine. After vaccination patients were re-tested and were all positive for IgG-VZV. We re-tested IgG-VZV in the same laboratory after a mean time of 2.42 years from Fingolimod therapy start. : During Fingolimod therapy we observed a global reduction of antibody titer and a disappearance in 7/11 patients. Titer disappearance was more probable in patients with lower post-vaccination titer. Of the 7 patients with vanishing IgG-VZV, three suspended Fingolimod for adverse event. In two of them, we observed a reappearance of antibody titer after treatment cessation. In one patient chickenpox infection occurred one year later. : Our observational study shows that Fingolimod could influence antibody titer probably through its effect on B lymphocytes, but the efficacy of the vaccination should be verified. In conclusion, it is necessary to pay attention to therapies acting on B lymphocytes as they could influence the antibody titer and efficacy of vaccination making the search for other markers of vaccine efficacy desirable such as cell-mediated immunity with proliferation and induction of memory T lymphocytes in response to viral glycoproteins.