Intravaginal delivery of mRNA-encoded antibodies with enhanced breadth and potency for SHIV/HIV protection

Broadly neutralizing antibodies (bnAbs) prevent HIV infection but face administration and cost challenges. We present single-chain mRNA-encoded bnAbs that improve heavy-light chain assembly and enable three enhancement approaches: co-expression, isotype selection, and engineered nanobodies. We observe enhanced in vitro neutralization through co-expression of PGT121 and VRC07 (targeting V3-glycan and CD4-binding site, respectively) and by replacing IgG constant heavy chain (IgG-C_H) with IgA-C_H or incorporating an IgM tailpiece into IgG-C_H. While IgG versions fail to neutralize several SHIV/HIV strains, co-expressing PGT121 and VRC07 as IgM-like multimers restores neutralizing capability (IC₅₀ < 100 ng/mL) and substantially improves breadth. Vaginal explants from rhesus macaques, treated with intravaginal aerosolized mRNAs, show robust protection against ex vivo challenges with multiple SHIV strains when PGT121 and VRC07 are co-expressed as IgM-like multimers. Our data present novel drug compositions for intravaginal mRNA delivery to prevent HIV acquisition and advance antibody-design strategies that enhance breadth and potency of existing bnAbs.