10E8-like neutralizing antibodies against HIV-1 induced using a precisely designed conformational peptide as a vaccine prime

Recent studies have demonstrated that the membrane-proximal external region (MPER) of human immunodeficiency virus 1 (HIV-1) glycoprotein 41 contains a series of epitopes for human monoclonal antibodies, including 2F5, Z13e1, 4E10, and 10E8, which were isolated from HIV-1-infected individuals and show broad neutralizing activities. This suggests that MPER is a good target for the development of effective HIV-1 vaccines. However, many studies have shown that it is difficult to induce antibodies with similar broad neutralizing activities using MPER-based peptide antigens. Here, we report that 10E8-like neutralizing antibodies with effective anti-HIV-1 activity were readily induced using a precisely designed conformational immunogenic peptide containing the 10E8-specific epitope. This immunogenic peptide (designated T10HE) contains a 15-mer MPER-derived 10E8-specific epitope fused to T-helper-cell epitopes from tetanus toxin (tt), which showed a significantly stabilized α-helix structure after a series of modifications, including substitution with an (S)-α-(2′-pentenyl) alanine containing an olefin-bearing tether and ruthenium-catalyzed olefin metathesis, compared with the unmodified T10E peptide. The stabilized α-helix structure of T10HE did not affect its capacity to bind the 10E8 antibody, as evaluated with an enzyme linked immunosorbent assay (ELISA) and surface plasmon resonance binding assay (SPR assay). The efficacies of the T10HE and T10E epitope vaccines were evaluated after a standard vaccination procedure in which the experimental mice were primed with either the T10HE or T10E immunogen and boosted with HIV-1 JRFL pseudoviruses. Higher titers of 10E8-like antibodies were induced by T10HE than that by T10E. More importantly, the antibodies induced by T10HE showed enhanced antiviral potency against HIV-1 strains with both X4 and R5 tropism and a greater degree of broad neutralizing activity than the antibodies induced by T10E. These results indicate that a 10E8-epitope-based structure-specific peptide immunogen can elicit neutralizing antibodies when used as a vaccine prime.