O2136: Transamniotic Fetal Delivery of Human alpha-1 Antitrypsin Mrna in a Healthy Rodent Model

Background: Alpha-1 antitrypsin (AAT) is a protein produced primarily in the liver to protect the lungs from inflammatory neutrophil elastase and other protease activity. AAT deficiency (AATD) is one of the most common inherited metabolic disorders which can manifest at any stage in life, including the perinatal period. Among its manifestations is obstructive lung disease, which can be severe and for which current therapies are of limited benefit. It has been shown that the transamniotic route can be a practical and effective method for delivering exogenous mRNA to the fetus, as a variant of the transamniotic nucleic acid therapy (TRANAT) principle. We sought to determine whether TRANAT could be a viable alternative for the administration of AAT mRNA to the fetal lungs and/or liver as a prospective novel strategy for the perinatal management of AATD.

Methods: After IACUC approval, twelve pregnant Sprague Dawley dams underwent midline laparotomy followed by volume-matched (50μL) intra-amniotic injections in all their fetuses (n=139) of either a suspension of a human AAT mRNA encapsulated by a lipid- and synthetic cationic polymer-based composite, lipopolyplex (mRNA group; n=99), or of a suspension of the same encapsulation composite but free of mRNA (control group; n=40), on gestational day 17 (E17; term=E21). At daily time points thereafter until term (E18, E19, E20, and E21), samples from fetal lung and liver were procured for screening for the presence of the exogenous mRNA-encoded human AAT protein via quantification by ELISA. Standard liver function panels were performed in subsets of animals at term. Statistical analysis included median regression to account for nesting of fetuses within dams, with significance set at p< 0.05.

Results: Overall fetal survival was 79% (110/139), but significantly higher in the mRNA group (p=0.012). When controlled by mRNA-free injections, there was evidence of human AAT production in the fetal lungs at all four daily time points (p=0.005 to < 0.001; figure). The levels of human AAT in the lungs were highest at E18 and tended to decrease thereafter, stabilizing one day before and at term (figure). Controlled by mRNA-free injections, human AAT was detected in the fetal liver only at E20, with levels significantly higher in the control group at E19 and E21, suggesting possible interspecies homology manifesting at that anatomical site. Term liver function panels were comparable between the groups.

Conclusion: Encapsulated exogenous mRNA encoding for human alpha-1 antitrypsin protein can be incorporated and translated by fetal lung cells following simple intra-amniotic injection in a healthy rat model. Fetal hepatic incorporation and translation remains to be determined in a model with minimal to no human homology. Transamniotic mRNA delivery could become a novel strategy for the perinatal management of alpha-1 antitrypsin deficiency.