Vaccination with mRNA-encoded membrane-anchored HIV envelope trimers elicited tier 2 neutralizing antibodies in a phase 1 clinical trial

mRNA technology might accelerate development of an urgently needed preventive human immunodeficiency virus (HIV) vaccine. We evaluated the safety and immunogenicity of three mRNA-encoded envelope trimers, including two doses of soluble and membrane-anchored forms, in a randomized, open-label, phase 1 clinical trial. Vaccines were generally well tolerated, although 6.5% (7 of 108) of participants developed urticaria, a higher proportion than seen with other mRNA vaccines. mRNA-encoded trimers induced strong envelope-specific B and T cell responses. Immunization with membrane-anchored trimers, intended to obscure epitopes at the trimer base targeted by nonneutralizing antibodies, reduced the frequency of base-binding serum antibodies in comparison with soluble trimers. Three immunizations elicited autologous tier 2 serum neutralizing antibodies in 80% of vaccinees receiving the membrane-anchored trimers, in contrast to only 4% receiving the soluble trimer. Thus, with demonstration of more favorable safety, mRNA-encoded membrane-anchored HIV envelope trimers represent a promising platform for HIV vaccine clinical development.