Mucosal administration of lipid nanoparticles containing self-amplifying mRNA induces local uptake and expression in a pig model as a potential vaccination platform against STIs

Mucosal vaccination generates protective immune responses directly at the primary site of STI infection. However, the delivery of nanoparticles is hindered by the mucus barrier at these mucosal surfaces. Due to this interference, research on mucosal administration of self-amplifying (sa)-mRNA encapsulated in lipid nanoparticles (LNP) is currently limited and inconsistent. Some progress has been reported for nasal mRNA vaccination. However, for STIs, protective immune responses are required at the urogenital tract, which is achieved through intravaginal or intranasal administration. Therefore, in this research, we aimed to determine whether an sa-mRNA-LNP reporter vaccine could be effectively administered mucosally, evaluating its potential as a novel platform for STI vaccination. The sa-mRNA luciferase construct was encapsulated in two LNP formulations. In vitro studies demonstrated that these formulations maintained their potency after being sprayed with different sprayers and exposed to different mucus solutions, except for a human cervicovaginal simulant. Next, pigs received 15 µg of the sa-mRNA intravaginally and intranasally through a mucosal spray or injection. The mucosal spray resulted in expression and uptake only at the vaginal mucosa, whereas injection of the formulations resulted in expression at both mucosal sites. However, expression after spraying in the vaginal mucosa disappeared by day 4 post-administration. No differences were observed between both LNP formulations. These findings demonstrate that sa-mRNA can be used for mucosal administration, and expression can be achieved in a more relevant animal model. However, additional research is needed to develop more suitable particles for these complex environments.