On placental and lactational transfer of IgG-based therapeutic proteins – Current understanding and knowledge gaps from a clinical pharmacology perspective

Maternal medication use may expose the developing fetus through placental transfer or the infant through lactational transfer. Because pregnant and lactating individuals have been historically excluded from early drug development trials, there is often limited to no human data available to inform pharmacokinetics (PK) and safety in these populations at the time of drug approval. We describe the known mechanisms of placental or lactational transfer of IgG-based therapeutic proteins and use clinical examples to highlight the potential for fetal or infant exposure during pregnancy and lactation. Placental transfer of IgG-based therapeutic proteins may result in systemic exposure to the developing fetus. A lactational transfer may be associated with local gastrointestinal (GI) exposure in the infant and may also result in systemic exposure, although data are very limited as proteins have shown instability in the GI tract. Understanding of PK and pharmacodynamic (PD) effects of IgG-based therapeutic proteins in infants exposed in utero as well as the potential exposure through human milk and its clinical implications is critical for developing treatment strategies for pregnant or lactating individuals. We share the current knowledge gaps and considerations for future evaluations to inform PK, PD, and the safety of IgG-based therapeutic proteins for safe use during pregnancy and lactation. With the increasing use of IgG-based therapeutic proteins in treating chronic diseases during pregnancy and lactation, there is a need to improve the quantity and quality of data to inform the safe use in pregnant and lactating individuals.