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

Abstract

The vaccine elicitation of broadly neutralizing antibodies against HIV-1 is a long-sought goal. We previously reported the amino-terminal eight residues of the HIV-1-fusion peptide (FP8) -when conjugated to the carrier protein, keyhole limpet hemocyanin (KLH) -to be capable of inducing broadly neutralizing responses against HIV-1 in animal models. However, KLH is a multi-subunit particle derived from a natural source, and its manufacture as a clinical product remains a challenge. Here we report the preclinical development of recombinant tetanus toxoid heavy chain fragment (rTTHC) linked to FP8 (FP8-rTTHC) as a suitable FP-conjugate vaccine immunogen. We assessed 16 conjugates, made by coupling the 4 most prevalent FP8 sequences with 4 carrier proteins: the aforementioned KLH and rttHc; the H. influenzae protein D (HiD); and the cross-reactive material from diphtheria toxin (CRM197). While each of the 16 FP8-carrier conjugates could elicit HIV-1-neutralizing responses, rTTHC conjugates induced higher FP-directed responses overall. A Sulfo-SIAB linker yielded superior results over an SM(PEG)2 linker but combinations of carriers, conjugation ratio of peptide to carrier, or choice of adjuvant (Adjuplex or Alum) did not significantly impact elicited FP-directed neutralizing responses in mice. Overall, SIAB-linked FP8-rTTHC appears to be a promising vaccine candidate for advancing to clinical assessment.The fusion peptide (FP) site of vulnerability on the HIV-1 envelope (Env) glycoprotein has recently been shown to be a promising vaccine target 1-3 . FP, a hydrophobic region of ~15 residues at the N terminus of the gp41 transmembrane glycoprotein, is an essential component of the HIV entry machinery 4 . FP embeds in the target cell membrane during the pre-hairpin intermediate stage of entry, where it serves to anchor the rearranging viral spike and to facilitate the merging of viral and cell membranes. The N-terminal portion of FP is solvent accessible and recognized by broadly neutralizing antibodies PGT151 5,6 , N123-VRC34.01 3 , and ACS202 7 . Because FP is a short linear peptide, it has low inherent immunogenicity due to its lack of helper T cell epitopes. Coupling peptides to highly immunogenic carrier proteins is a well-established approach for providing T cell help to peptide immunogens [8][9][10][11] . When the N-terminal 6-10 residues of FP are coupled to keyhole limpet hemocyanin (KLH), a standard protein carrier widely used in biotechnology, the resultant FP-KLH conjugate immunogens are able to induce broadly neutralizing FP-directed immune responses in mice, guinea pigs, and rhesus macaques 1,2,12 . Vaccine-induced FP-directed antibodies from mice or NHP neutralize up to 31% or 59%, respectively, of a cross-clade panel of 208 HIV-1 strains 2 .These results (illustrated in Fig. 1a) indicate FP coupled to a carrier protein to be a promising candidate immunogen. However, KLH is a multi-subunit metalloprotein derived from natural sources 13-15 with both sequence and glycan heterogeneity, which pose manufacturin...

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

“…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].…”

Polyclonal antibody responses to HIV Env immunogens resolved using cryoEM

“…The fusion peptide epitope is a well-explored target for bnAbs and is the focus of ongoing HIV vaccine design efforts (Kong et al, 2019, Ou et al, 2020, Xu et al, 2018). We compared the Rh.33311 pAbC-1 structure to the available bnAb structures (Figure S6A).…”

New SHIVs and Improved Design Strategy for Modeling HIV-1 Transmission, Immunopathogenesis, Prevention and Cure

“…In recent years, there have been notable advances in HIV prevention and cure research (79)(80)(81)(82)(83) At the same time, Env is the target of an array of neutralizing antibodies and cytotoxic T-cells that cause it to evolve continuously in order to escape recognition that would otherwise lead to virus 20 elimination (38,86,87). Env accomplishes the latter by means of highly evolved properties, including occlusion of trimer-interface epitopes (88), epitope variation (89), conformational masking (90) and glycan shielding (91).…”

“…In recent years, there have been notable advances in HIV prevention and cure research (79–83) yet the goals of effective vaccination and cure – even a “functional” cure – seem far in the distance. Increasingly, experimental medicine trials in humans have been pursued as a strategy to accelerate translational research (82), but at the same time, there remain untapped opportunities and needs for animal models to complement and synergize with human studies to hasten progress.…”