BACKGROUND ABT-874 is an anti-IL-12/23 monoclonal antibody that binds to the p40 subunit of human IL-12 and IL-23. As part of its preclinical safety assessment, studies were conducted to assess its potential effects on pre- and postnatal development in cynomolgus monkeys. METHODS In the embryo-fetal development studies, ABT-874 was administered once weekly subcutaneously to adult female cynomolgus monkeys at doses of 0, 5, 25, or 100 mg/kg during gestation days (GD) 20 to 48. Fetuses were examined for external, visceral, and skeletal development on GD 100 or 150. In the pre- and postnatal study, ABT-874 was administered once weekly subcutaneously to adult female cynomolgus monkeys at doses of 10, 50, or 200 mg/kg from GD 20 through postpartum day 182. Infants were examined from birth up to 9 months of age for morphological and functional development. Potential effects on the infant immune system were evaluated by immunophenotyping of peripheral blood lymphocytes and by T-dependent antibody response to KLH. RESULTS There was no ABT-874-related maternal toxicity or adverse effects on fetuses or infants. ABT-874 was present in maternal and fetal serum at GD 100 and 150, and in infant serum through day 63 postbirth. ABT-874 was also present at low levels in breast milk through postpartum day 175. CONCLUSIONS Exposure of cynomolgus monkey fetuses and infants to ABT-874 had no adverse effects on embryo-fetal or postnatal development.