A long-lasting prolactin to combat lactation insufficiency

Human infants are born to breastfeed. While 50% of lactating persons report struggling to make enough milk, there are no governmentally-approved drugs to enhance lactation1. Here, we engineer a variant of the naturally-occurring driver of lactation, the hormone Prolactin, to increase its serum half-life and produce a viable drug candidate. Our engineered variant,Prolactin-eXtra Long-acting(Prolactin-XL), is comprised of endogenously active human prolactin fused to an engineered human IgG1 Fc domain designed to overcome the unique drug development challenges specific to the lactating person-infant dyad. Our Prolactin-XL has a serum half-life of 70.9h in mice, 2,625-fold longer than endogenously active prolactin alone (70.9h v. 0.027h). We demonstrate that Prolactin-XL increases milk production and restores growth of pups fed by dams with pharmacologically-ablated lactation. We show that Prolactin-XL-enhanced lactation is accompanied by reversible, alveolar cell-driven changes in mammary gland morphology. Prolactin-XL treatment was associated with no identifiable pathology or adverse side effect in the lactating mice or nursing pups. This work establishes long-acting prolactins as a potentially powerful pharmacologic means to combat insufficient lactation. Implications for future research in lactating mammary gland biology and a potential preclinical path for developing Prolactin-XL for use in lactating persons are discussed.