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Background: Multiple sclerosis (MS) predominantly affects women, and the clinical onset of MS often occurs during child-bearing age. Clinicians recommend discontinuation of disease-modifying therapies (DMTs) before conception unless the risk of disease worsening outweighs the risk to the fetus. New high-efficacy DMTs such as rituximab, a chimeric monoclonal B-cell-depleting anti-CD20 antibody, are frequently used off-label for the treatment of MS in Sweden. Objective: There is a lack of evidence on the influence of DMTs including anti-CD20-antibodies on the infant´s immune system and their responses to vaccination during the first months after birth. Purpose: To fill the knowledge gaps regarding the impact of the mother´s DMT on a newborn´s humoral immune system. Aims: To investigate the association between mother´s exposure to DMTs pre-pregnancy and infant´s 1) successful B-cell production 2) vaccine response and 3) risk of infections within the first year. Setting: a) Retrospective cohort study with infants born between 2012 and 2022 to mothers with MS treated with DMTs. The infants´humoral immune system will be assessed by analyzing markers of successful B-cell production in newborn dried-blood spot samples. b) Prospective cohort study, recruiting between 2024 och 2025. Vaccine responses and infection rates in infants to mothers with rituximab will be compared to mothers with other DMTs prior to pregnancy.