Synthesis, conformation, and immunogenicity of monosaccharide-centered multivalent HIV-1 gp41 peptides containing the sequence of DP178

Modulating immunogenic properties of HIV-1 gp41 membrane-proximal external region by destabilizing six-helix bundle structure

The C-terminal alpha-helix of gp41 membrane-proximal external region (MPER; (671)NWFDITNWLWYIK(683)) encompassing 4E10/10E8 epitopes is an attractive target for HIV-1 vaccine development. We previously reported that gp41-HR1-54Q, a trimeric protein comprised of the MPER in the context of a stable six-helix bundle (6HB), induced strong immune responses against the helix, but antibodies were directed primarily against the non-neutralizing face of the helix. To better target 4E10/10E8 epitopes, we generated four putative fusion intermediates by introducing double point mutations or deletions in the heptad repeat region 1 (HR1) that destabilize 6HB in varying degrees. One variant, HR1-∆10-54K, elicited antibodies in rabbits that targeted W672, I675 and L679, which are critical for 4E10/10E8 recognition. Overall, the results demonstrated that altering structural parameters of 6HB can influence immunogenic properties of the MPER and antibody targeting. Further exploration of this strategy could allow development of immunogens that could lead to induction of 4E10/10E8-like antibodies.

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

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 ((671)NWFDITNWLWYIK(683)). 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.

A fusion intermediate gp41 immunogen elicits neutralizing antibodies to HIV-1

The membrane-proximal external region (MPER) of the human immunodeficiency virus, type 1 (HIV-1) envelope glycoprotein subunit gp41 is targeted by potent broadly neutralizing antibodies 2F5, 4E10, and 10E8. These antibodies recognize linear epitopes and have been suggested to target the fusion intermediate conformation of gp41 that bridges viral and cellular membranes. Anti-MPER antibodies exert different degrees of membrane interaction, which is considered to be the limiting factor for the generation of such antibodies by immunization. Here we characterize a fusion intermediate conformation of gp41 (gp41(int)-Cys) and show that it folds into an elongated ∼ 12-nm-long extended structure based on small angle x-ray scattering data. Gp41(int)-Cys was covalently linked to liposomes via its C-terminal cysteine and used as immunogen. The gp41(int)-Cys proteoliposomes were administered alone or in prime-boost regimen with trimeric envelope gp140(CA018) in guinea pigs and elicited high anti-gp41 IgG titers. The sera interacted with a peptide spanning the MPER region, demonstrated competition with broadly neutralizing antibodies 2F5 and 4E10, and exerted modest lipid binding, indicating the presence of MPER-specific antibodies. Although the neutralization potency generated solely by gp140(CA018) was higher than that induced by gp41(int)-Cys, the majority of animals immunized with gp41(int)-Cys proteoliposomes induced modest breadth and potency in neutralizing tier 1 pseudoviruses and replication-competent simian/human immunodeficiency viruses in the TZM-bl assay as well as responses against tier 2 HIV-1 in the A3R5 neutralization assay. Our data thus demonstrate that liposomal gp41 MPER formulation can induce neutralization activity, and the strategy serves to improve breadth and potency of such antibodies by improved vaccination protocols.

Strategy for Designing a Synthetic Tumor Vaccine: Multi-Component, Multivalency and Antigen Modification

Synthetic tumor vaccines have been proven to be promising for cancer immunotherapy. However, the limitation of the specificity and efficiency of the synthetic tumor vaccines need further improvements. To overcome these difficulties, additional tumor-associated targets need to be identified, and optimized structural designs of vaccines need to be elaborated. In this review, we summarized the main strategies pursued in the design of synthetic tumor vaccines, such as multi-component, multivalency, antigen modification and other possible ways to improve the efficiency of synthetic tumor vaccines.

A multivalent HIV-1 fusion inhibitor based on small helical foldamers

The peptide sequence AcNH-TEG-Glu-Aib-Trp-AibAib-Trp-AibAib-Ile-Asp-OH (1), designed to display the WWI epitope found near the C-terminus of gp41, an envelope glycoprotein decorating the surface of the HIV-1 virus, has been synthesized and proved to have a relevant content of helical conformation because of the presence of five α-aminoisobutyric acid (Aib) units. Three copies of it have been connected to a tripodal platform based on 2,4,6-triethylbenzene-1,3,5-trimethylamine. The tripodal template 2 is even more structured than 1 thus suggesting a significant interaction between the three sequences connected to the platform. Preliminary inhibition assays of HIV-mediated cell fusion indicated that while the single peptide 1 is inactive within the concentration range of our assay, when it is conjugated to the tripodal platform, it is moderately active. These promising results suggest that our approach constitute a valid alternative to those reported so far.

Current status of multiple antigen-presenting peptide vaccine systems: Application of organic and inorganic nanoparticles

Many studies are currently investigating the development of safe and effective vaccines to prevent various infectious diseases. Multiple antigen-presenting peptide vaccine systems have been developed to avoid the adverse effects associated with conventional vaccines (i.e., live-attenuated, killed or inactivated pathogens), carrier proteins and cytotoxic adjuvants. Recently, two main approaches have been used to develop multiple antigen-presenting peptide vaccine systems: (1) the addition of functional components, e.g., T-cell epitopes, cell-penetrating peptides, and lipophilic moieties; and (2) synthetic approaches using size-defined nanomaterials, e.g., self-assembling peptides, non-peptidic dendrimers, and gold nanoparticles, as antigen-displaying platforms. This review summarizes the recent experimental studies directed to the development of multiple antigen-presenting peptide vaccine systems.

Broad neutralization of human immunodeficiency virus type 1 (HIV-1) elicited from human rhinoviruses that display the HIV-1 gp41 ELDKWA epitope

In efforts to develop AIDS vaccine components, we generated combinatorial libraries of recombinant human rhinoviruses that display the well-conserved ELDKWA epitope of the membrane-proximal external region of human immunodeficiency virus type 1 (HIV-1) gp41. The broadly neutralizing human monoclonal antibody 2F5 was used to select for viruses whose ELDKWA conformations resemble those of HIV. Immunization of guinea pigs with different chimeras, some boosted with ELDKWA-based peptides, elicited antibodies capable of neutralizing HIV-1 pseudoviruses of diverse subtypes and coreceptor usages. These recombinant immunogens are the first reported that elicit broad, albeit modest, neutralization of HIV-1 using an ELDKWA-based epitope and are among the few reported that elicit broad neutralization directed against any recombinant HIV epitope, providing a critical advance in developing effective AIDS vaccine components.

Design and Synthesis of Lipopeptide - Carbohydrate Assembled Multivalent Vaccine Candidates Using Native Chemical Ligation

Development of a synthetic vaccine against group A streptococcal infection is increasingly paramount due to the induction of autoimmunity by the main virulent factor – M protein. Peptide vaccines, however, are generally poorly immunogenic, necessitating administration with carriers and adjuvants. One of the promising approaches to deliver antigenic peptides is to assemble peptides on a suitable template which directs the attached peptides to form a well defined tertiary structure. For self-adjuvanting human vaccines, the conjugation of immunostimulatory lipids has been demonstrated as a potentially safe method. This study describes the design and optimized synthesis of two lipopeptide conjugated carbohydrate templates and the assembling of peptide antigens. These lipopeptide–carbohydrate assembled multivalent vaccine candidates were obtained in high yield and purity when native chemical ligation was applied. Circular dichroism studies indicated that the template-assembled peptides form four α-helix bundles. The developed technique extends the use of carbohydrate templates and lipopeptide conjugates for producing self-adjuvanting and topology-controlled vaccine candidates.

Lipid Core Peptide System for Gene, Drug, and Vaccine Delivery

A vast number of biologically active compounds await efficient delivery to become therapeutic agents. Lipidation has been demonstrated to be a convenient and useful approach to improve the stability and transport across biological membranes of potential drug molecules. The lipid core peptide (LCP) system has emerged as a promising lipidation tool because of its versatile features. This review discusses the progress in the development of the LCP system to improve cell permeability of nucleotides, physicochemical properties of potential drugs, and vaccine immunogenicity. Emphasis was put on the application of the LCP system to deliver antigens for the prevention of group A streptococcus infection, novel techniques of conjugation of target molecules to the LCP, and new alterations of the LCP system itself.

The membrane-proximal external region of the human immunodeficiency virus type 1 envelope: dominant site of antibody neutralization and target for vaccine design

Enormous efforts have been made to produce a protective vaccine against human immunodeficiency virus type 1; there has been little success. However, the identification of broadly neutralizing antibodies against epitopes on the highly conserved membrane-proximal external region (MPER) of the gp41 envelope protein has delineated this region as an attractive vaccine target. Furthermore, emerging structural information on the MPER has provided vaccine designers with new insights for building relevant immunogens. This review describes the current state of the field regarding (i) the structure and function of the gp41 MPER; (ii) the structure and binding mechanisms of the broadly neutralizing antibodies 2F5, 4E10, and Z13; and (iii) the development of an MPER-targeting vaccine. In addition, emerging approaches to vaccine design are presented.