Antibody Lineages with Vaccine-Induced Antigen-Binding Hotspots Develop Broad HIV Neutralization

Abstract

SUMMARY The vaccine-mediated elicitation of antibodies (Abs) capable of neutralizing diverse HIV-1 strains has been a long-standing goal. To understand how broadly neutralizing antibodies (bNAbs) can be elicited, we identified, characterized, and tracked five neutralizing Ab lineages targeting the HIV-1-fusion peptide (FP) in vaccinated macaques over time. Genetic and structural analyses revealed two of these lineages to belong to a reproducible class capable of neutralizing up to 59% of 208 diverse viral strains. B cell analysis indicated each of the five lineages to have been initiated and expanded by FP-carrier priming, with envelope (Env)-trimer boosts inducing cross-reactive neutralization. These Abs had binding-energy hotspots focused on FP, whereas several FP-directed Abs induced by immunization with Env trimer-only were less FP-focused and less broadly neutralizing. Priming with a conserved subregion, such as FP, can thus induce Abs with binding-energy hotspots coincident with the target subregion and capable of broad neutralization.

Preclinical Development of a Fusion Peptide Conjugate as an HIV Vaccine Immunogen

“…To develop FP-carrier conjugates as immunogens for clinical evaluation, we analyzed the prevalence of FP sequences in the HIV LANL database 34 . The N-terminal 6 residues of FP account for 72% of the FP interface-buried surface area, when complexed with the broadly neutralizing FP-directed antibody N123-VRC34.01 3 , and we observed a similar focus on the N-terminal 6-8 residues of FP in FP-directed HIV-1 neutralizing antibodies elicited in mice and macaques 2,12 . The N-terminal FP residues are variably conserved, with a cumulative frequency of the top 4 most prevalent N-terminal sequences of FP6 (residues 512-517 of Env) utilized by ~65% of the HIV-1 isolates in the LANL database and the top 4 most prevalent N-terminal sequences of FP8 (residues 512-519 of Env) utilized by ~35% of the HIV-1 isolates in the LANL database ( Fig.…”

“…While FP-carrier protein priming is important for initiating FP-directed responses 12 , Env trimer boosts are also important to mature the responses into potent broad neutralization 1,2,12 . Furthermore, our results suggest that compared to Adjuplex, use of Alum as an adjuvant resulted in slower development of anti-FP responses during the FP8v1-rTTHC priming stage, though these responses continued to develop upon trimer boosting, ultimately yielding similar responses as induced by Adjuplex at the end of the study.…”

Development of Antibodies with Broad Neutralization Specificities against HIV-1 after Long Term SHIV Infection in Macaques

“…Using the epitope focusing approach, a more recent study showed that the FP-coupled carrier protein immunogens could induce cross-reactive FP-targeted neutralization activities in mice, guinea pigs and NHPs [19,20]. More importantly, mAbs representing the similar neutralization breadth in sera were successfully isolated from several of immunized macaques [21]. These results demonstrate the important roles of bnAbs and possibility to elicit them in NHPs.…”

Innovations in structure-based antigen design and immune monitoring for next generation vaccines

“…One approach to focus the response on the FP is through repeated immunization with 10-100s of copies of the FP displayed on carrier proteins, such as keyhole limpet hemacyanin (KLH), followed by a booster immunization with the Env trimer spike to present the FP in a more native context. This approach has produced encouraging responses in animals with up to 31% and 59% neutralization breadth in mice and macaques, respectively, against panel of diverse HIV isolates [27,28]**. This concept is now being developed for human clinical trials [29].…”