Clostridioides difficile Immunity During Pregnancy and Passive Antibody Transfer to Neonates from Cord Blood and Breast Milk

Passive transplacental immunity is crucial for neonatal protection from infections. Following <i>Clostridioides difficile</i> (<i>C. difficile</i>) infection, infants do not develop disease, although <i>C. difficile</i> colonization is highly prevalent in infants. This work aimed to characterize humoral immunity specific to <i>C. difficile</i> toxins TcdA and TcdB and to surface proteins FliD and Cwp84, well-known colonizing factors, in pregnant women and their neonates. Anti-<i>C. difficile</i> antibodies were measured in maternal serum, cord blood, and breast milk from 58 healthy pregnant women and their newborns, enrolled in a prospective study, using a quantitative ELISA. Anti-<i>C. difficile</i> antibodies were also measured in pregnant women with <i>C. difficile</i> infection (CDI) in a retrospective peripartum case series. We found a high seroprevalence of IgG specific to the four antigens in healthy pregnant women, regardless of colonization by <i>C. difficile</i>. However, pregnant women exhibited lower concentrations of TcdA-specific IgG antibodies compared to age-matched non-pregnant women. A strong positive correlation between maternal and cord blood IgG specific to TcdA, TcdB, FliD, and Cwp84 was observed, suggesting a transplacental transfer of <i>C. difficile</i>-specific IgG antibodies to neonates. In breast milk, a high seroprevalence of IgA specific to the two toxins was detected, and positive correlations between maternal serum and breast milk antibody levels highlight a preferential transfer of TcdB-specific IgG and Cwp84-specific IgG to breast milk, providing the infant with a protective barrier against <i>C. difficile</i>. Lastly, since pregnant women are at increased risk for <i>C. difficile</i> infection (CDI), we characterized the specific antibody response in a retrospective peripartum case series. Sera from peripartum women with CDI exhibited similar median concentrations of TcdA, TcdB, FliD, and Cwp84 IgM and IgG to those of healthy pregnant women. Moreover, except for one case, antibody concentrations remained stable during the longitudinal evolution of <i>C. difficile</i> response before and after diagnosis of CDI, without any booster effect. Altogether, these data are consistent with antibody-mediated maternal protection of neonates from <i>C. difficile</i>-associated disease. Larger studies exploring immune factors involved in protection from <i>C. difficile</i>-associated disease during pregnancy are needed.