Natalizumab during pregnancy and lactation

Background: Managing medication during pregnancy and lactation in multiple sclerosis (MS) patients needs to balance potential risks to the newborn with the substantial risks of ongoing disease activity. Objective: To evaluate the potential transfer of natalizumab (NAT) into breast milk and into the serum of newborn babies in women who continued NAT treatment during pregnancy and lactation. Methods: Serum samples of 11 mother-infant pairs and mother milk samples of a further 4 women were analyzed for free NAT using a HL60 cell-based fluorescence-activated cell sorting (FACS) assay. Two mother-baby pairs were analyzed for cell-bound NAT, very-late-antigen (VLA)-4 expression, and saturation with NAT on immune cells by FACS analysis. Results: In the majority of the mother-infant serum pairs (6/11) and in all breast milk samples, free NAT was detectable. Cell-bound NAT was measurable in both mother-baby pairs with significant higher levels in babies. VLA-4 expression seems to be higher in newborns. Saturation with NAT was comparable between newborns and mothers. Conclusion: NAT can pass placental barrier before delivery and into breast milk. Measurable NAT on neonatal lymphocytes may have functional impact. Further investigations are needed to clarify safety and risk of NAT exposure during pregnancy and lactation.