To generate functional anti-protease-activated receptor-4 (PAR4), a G protein-coupled receptor, antibodies through...

G protein-coupled receptors (GPCRs) are key therapeutic targets for various diseases, such as the thrombin receptor protease-activated receptor 4 (PAR4) involved in thrombotic cardiovascular disorders. However, the structural complexity of native GPCRs hinders recombinant protein production, making peptide-based immunization insufficient for generating high-quality antibodies. Here, we developed a PAR4-mRNA-LNP vaccine to express native PAR4 in vivo, thereby inducing potent and specific anti-PAR4 antibodies. The PAR4-mRNA-LNP formulation showed 93.44% encapsulation efficiency, an average size of 127.5 nm, and a polydispersity index (PDI) of 0.1033. Native 55-kDa PAR4 protein with complete glycosylation was confirmed on the cell surface using western blotting and flow cytometry. Mice immunized with PAR4-mRNA-LNP produced strong anti-PAR4 antibody responses, as detected by cell-based ELISA. Finally, we established hybridoma cell lines and identified five clones that significantly inhibited PAR4-mediated platelet aggregation. These findings suggest that mRNA-LNP technology can be broadly applied to generate functional anti-GPCR antibodies for therapy.