Despite the success of postexposure prophylaxis (PEP) of the newborn in preventing mother-to-child transmission of hepatitis\nB virus), in non-US clinical trials, administering hepatitis B immune globulin (HBIG) to mothers at the end of pregnancy (in\naddition to passive-active PEP of the newborn) only partially improved outcomes. That is, a significant percentage of newborns\nbecame infected during their first year of life. We used a relevant animal model for human IgG transplacental transfer to study\ndose, time and subclass dependence ofHBVneutralizing antibody (nAb) maternal, and fetal levels at the end of pregnancy. Pregnant\nguinea pigs received 50 or 100 IU/kg HBIGIV 2ââ?¬â??5 days before delivery. Human total IgG, IgG subclasses, and nAb in mothers and\ntheir litters were measured.In vitro analyses of guinea pig Fc neonatal receptor binding to HBIGIV, as well as to all human IgG\nsubclasses, were also performed. Our study showed that nAb transferred transplacentally from the pregnant guinea pigs to their\nlitters; no transfer occurred during parturition.The amount of the transferred nAb was dose and time dependent.Thus, selection\nof an efficacious dose in the clinic is important: microdosing may be underdosing, particularly in cases of high viraemia.
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