CD19 thorn B cell values predict the increase of anti-SARS CoV2 antibodies in fingolimod-treated and COVID-19-vaccinated patients with multiple sclerosis

Background: Treatment with fingolimod for multiple sclerosis (MS) reduces the efficacy of COVID-19 vaccina-tion. The aim of this exploratory study was to evaluate whether main lymphocyte subsets and demographic features correlated to the subsequent increase in anti-SARS-CoV2 antibodies following the third dose of COVID-19 vaccination in fingolimod-treated MS patients.Methods: This was a prospective single-center observational exploratory study including a subgroup of adult patients with MS (pwMS) in treatment with fingolimod who underwent COVID-19 vaccination. The association of anti-SARS-CoV2 antibody levels (reported as the Log10 of the difference between the post and pre third dose levels) with the total number and percentage of CD3+ T and CD19+ B was assessed by a linear regression model adjusted for age and sex.Results: We found that peripheral blood CD19+ B lymphocytes before the third dose of vaccination in pwMS treated with fingolimod predict the subsequent increase of anti-SARS-CoV2 antibodies.Conclusion: This work suggests that evaluating the percentage of CD19+ B cells may be important to identify patients at risk of not producing SARS-CoV-2 antibodies, with possible reduced protection from COVID-19.