Immunogenic properties of a trimeric gp41-based immunogen containing an exposed membrane-proximal external region

•An M group consensus sequence-based HIV-1 gp41 MPER immunogen was generated.•Strong antibody responses were induced against the C-terminal 13 residues of MPER.•MPER antibodies competed against 4E10 and 10E8, but failed to neutralize HIV-1.•Epitope mapping analyses revealed critical insights on protein׳s immunogenicity.•Results from this study should facilitate future MPER-based immunogen design.

The membrane-proximal external region (MPER) of HIV-1 gp41 is an attractive target for vaccine development. Thus, better understanding of its immunogenic properties in various structural contexts is important. We previously described the crystal structure of a trimeric protein complex named gp41-HR1-54Q, which consists of the heptad repeat regions 1 and 2 and the MPER. The protein was efficiently recognized by broadly neutralizing antibodies. Here, we describe its immunogenic properties in rabbits. The protein was highly immunogenic, especially the C-terminal end of the MPER containing 4E10 and 10E8 epitopes (671NWFDITNWLWYIK683). Although antibodies exhibited strong competition activity against 4E10 and 10E8, neutralizing activity was not detected. Detailed mapping analyses indicated that amino acid residues critical for recognition resided on faces of the alpha helix that are either opposite of or perpendicular to the epitopes recognized by 4E10 and 10E8. These results provide critical information for designing the next generation of MPER-based immunogens.