Immunogenicity of recombinant influenza virus haemagglutinin carrying peptides from the envelope protein of human immunodeficiency virus type 1

Characterization of Salmonella typhi OmpC and OmpF porins engineered with HIV-gp41 epitope on the surface loops

Porins form trimers in the outer membrane and help transport nutrients and waste products across the bacterial cell membrane. Porin loops are suitable candidates as display systems due to their high immunogenicity and presentation at the bacterial cell surface. In this study, Salmonella typhi porins (OmpC and OmpF) engineered with the Kennedy peptide from gp41 of HIV were characterised. The chimeric OmpC carrying the Kennedy peptide in loop7 did not trimerise, whereas the chimeric OmpF with the epitope in loop5 formed trimers and also was recognised by the antibodies in the HIV patient serum. The results suggest that chimeric S. typhi OmpF may be taken further as a potential candidate to develop as an epitope display system. Proteins 2017; 85:657-664. © 2016 Wiley Periodicals, Inc.

Expression and immunological characterization of cardamom mosaic virus coat protein displaying HIV gp41 epitopes

The coat protein of cardamom mosaic virus (CdMV), a member of the genus Macluravirus, assembles into virus-like particles when expressed in an Escherichia coli expression system. The N and C-termini of the coat protein were engineered with the Kennedy peptide and the 2F5 and 4E10 epitopes of gp41 of HIV. The chimeric proteins reacted with sera from HIV positive persons and also stimulated secretion of cytokines by peripheral blood mononuclear cells from these persons. Thus, a system based on the coat protein of CdMV can be used to display HIV-1 antigens.

Recombinant influenza viruses as delivery vectors for hepatis B virus epitopes

Purpose

Neuraminidase (NA) of influenza virus contains stalk region that shows a great deal of variability in both amino acid sequence and length. In this paper, we investigated generation of recombinant influenza viruses that had hepatitis B virus (HBV) B cell epitopes in the NA stalk region as a dual vaccine candidate.

Materials and Methods

We used the WSH-HK reassortant helper virus for rescue of recombinant influenza virus containing HBV epitopes and reverse genetic protocol based on the use of micrococcal nuclease-treated virus cores for reconstitution of ribonucleoproteins.

Results

We successfully generated a chimeric influenza viruses which contained 22 amino acid peptides in the stalk region derived from the surface and pre-surface protein HBV. The growth kinetics of the recombinant viruses was investigated after infection of Madin-Darby canine kidney (MDCK) and Madin-Darby bovine kidney (MDBK) cells and the rIV-BVPreS virus showed higher titer than other viruses in MDCK cells. We also confirmed the presence of HBV epitopes in the chimeric viruses by enzyme-linked immunosorbent assay (ELISA) using anti-HBV polyclonal antibody. When the ratio of recombinant virus verse wild type virus was calculated by ELISA, recombinant viruses exhibited 2 fold higher values than the wild type virus.

Conclusion

These results suggest that chimeric influenza virus which contained foreign antigens can be used as dual vaccine against both HBV and influenza viruses.

Alkylated derivatives of poly(ethylacrylic acid) can be inserted into preformed liposomes and trigger pH-dependent intracellular delivery of liposomal contents

Poly(ethylacrylic acid) (PEAA) is a pH-sensitive polymer that undergoes a transition from a hydrophilic to a hydrophobic form as the pH is lowered from neutral to acidic values. In this work we show that pH sensitive liposomes capable of intracellular delivery can be constructed by inserting a lipid derivative of PEAA into preformed large unilamellar vesicles (LUV) using a simple one step incubation procedure. The lipid derivatives of PEAA were synthesized by reacting a small proportion (3%) of the carboxylic groups of PEAA with C10 alkylamines to produce C10-PEAA. Incubation of C10-PEAA with preformed LUV resulted in the association of up to 8% by weight of derivatized polymer with the LUV without inducing aggregation. The resulting C10-PEAA-LUV exhibited pH-dependent fusion and leakage of LUV contents on reduction of the external pH below pH 6.0 as demonstrated by lipid mixing and release of calcein encapsulated in the LUV. In addition, C10-PEAA-LUV exhibited pH dependent intracellular delivery properties following uptake into COS-7 cells with appreciable delivery to the cell cytoplasm as evidenced by the appearance of diffuse intracellular calcein fluorescence. It is demonstrated that the cytoplasmic delivery of calcein by C10-PEAA-LUV could be inhibited by agents (bafilomycin or chloroquine) that inhibit acidification of endosomal compartments, indicating that this intracellular delivery resulted from the pH-dependent destabilization of LUV and endosomal membranes by the PEAA component of the C10-PEAA-LUV. It is concluded that C10-PEAA-LUV represents a promising intracellular delivery system for in vitro and in vivo applications.

The human immunodeficiency virus type 1 envelope spike of primary viruses can suppress antibody access to variable regions

The human immunodeficiency virus type 1 (HIV-1) envelope spike is a heavily glycosylated trimeric structure in which protein surfaces conserved between different HIV-1 isolates are particularly well hidden from antibody recognition. However, even variable regions on the spike tend to be less antigenic and immunogenic than one might have anticipated for external structures. Here we show that the envelope spike of primary viruses has an ability to restrict antibody recognition of variable regions. We show that access to an artificial epitope, introduced at multiple positions across the spike, is frequently limited, even though the epitope has been inserted at surface-exposed regions on the spike. Based on the data, we posit that restricted antibody access may be the result, at least in part, of a rigidification of the epitope sequence in the context of the spike and/or a highly effective flexible arrangement of the glycan shield on primary viruses. Evolution of the HIV envelope structure to incorporate extra polypeptide sequences into nominally accessible regions with limited antibody recognition may contribute to reducing the magnitude of antibody responses during infection and allow the virus to replicate unhindered by antibody pressure for longer periods.

[Designing an effective AIDS vaccine: strategies and current status]

PURPOSE

The human immunodeficiency virus (HIV) and the acquired immunodeficiency syndrome induce account for over 40 million deaths in the past 20 years. Given that the currently available treatments to prevent HIV transmission and disease are not effective in eradicating the virus, vaccination likely represents the only efficacious adapted response to the global impact of this infection. This paper reviews the challenges encountered in the development of an HIV vaccine as well as the different vaccine approaches and main HIV vaccine candidates evaluated in clinical trials.

CURRENT KNOWLEDGE AND KEY POINTS

In spite the tremendous progress in HIV research, the major challenges that are encountered in the development of an HIV vaccine remain of scientific order and include viral specificities, absence of correlates of immune protection and limitations of existing animal models. Over 30 vaccine candidates have been evaluated in clinical trials. These vaccine approaches include the use of recombinant envelope proteins, DNA vaccines, live-vectored recombinant vaccines, subunit vaccines and prime-boost regimens combining various vaccine candidates. Although the protective efficacy of these candidate vaccines has yet to be demonstrated, some vaccination regiments appear to dampen initial viremia and prolong disease-free survival.

FUTURE PROSPECTS AND PROJECTS

Faced with the challenges in developing an HIV vaccine, international consortia and new methodologies have been proposed in order to accelerate the development and screening process of new candidate HIV vaccines. Moreover, in the absence of a protective vaccine, the impact of a vaccine that confers partial protection needs to be seriously considered.

The complex antigenicity of a small external region of the C-terminal tail of the HIV-1 gp41 envelope protein: a lesson in epitope analysis

The newly discovered external tail loop within the C-terminal tail of the gp41 transmembrane subunit of the HIV-1 envelope protein comprises approximately 40 residues, and within this are 18-residues ((734)PDRPEGIEEEGGERDRDR(751)) that include three antibody-reactive regions. The antigenicity is complex, and changes according to the biological context of the gp41. It is thus of interest both to the HIV specialist and protein immunologists. The antibody-reactive region, centred on the sequence ERDRD, encompasses three distinct epitopes which are expressed in different combinations on infected cells, wt virions, prefusion virion-cell complexes, and a neutralising antibody escape mutant virion. In addition ERDRD-specific antibodies have one or more antiviral activities, and variously neutralise the infectivity of free virions, neutralise virions already attached to the target cell, reduce the production of infectious progeny, and inhibit the ability of infected cells to fuse with non-infected cells. Antibodies to PDRPEG and IEEE have no apparent antiviral activity even though the footprints of the IEEE- and ERDRD-specific antibodies overlap. This review marshals the available experimental data with the aim of understanding the significance of the gp41 tail loop to the HIV-1 life cycle, and its relevance to potential anti-viral measures. There are lessons here, too, that are relevant to the comprehension of the antigenicity of short protein segments in general.

Biomembrane-Active Molecular Switches as Tools for Intracellular Drug Delivery

Many therapeutic strategies, such as gene therapy and vaccine development require the delivery of polar macromolecules (e.g. DNA, RNA, and proteins) to intracellular sites at a therapeutic concentration. For such macromolecular therapeutics, cellular membranes constitute a major transport barrier that must be overcome before these drugs can exert their biological activity inside cells. A number of biological organisms, e.g. viruses and toxins, efficiently destabilize the cellular membranes upon a trigger, such as low pH, and facilitate the delivery of their biological cargo to the cytoplasm of host cell. pH-responsive synthetic peptides and polymers have been designed to mimic the function of membrane-destabilizing natural organisms and evaluated as a part of drug delivery systems. In this Review, pH-dependent membrane activity of natural and synthetic systems is reviewed, focussing on fundamental and practical aspects of pH-responsive, membrane-disruptive synthetic polymers in intracellular drug delivery.

Toward novel vaccines and therapies based on negative-strand RNA viruses

The study of negative-strand RNA viruses has suggested new strategies to produce more attenuated viruses. Reverse genetics has allowed the implementation of the strategies, and new or improved monovalent vaccines are being developed. In addition, recombinant viruses expressing foreign proteins or epitopes have been produced with the aim of developing multivalent vaccines capable of stimulating humoral and cellular immune responses against more than one pathogen. Finally, recombinant viruses that selectively enter cells expressing tumor markers or the HIV envelope protein have been engineered and shown to lyse target cells. Preclinical and clinical trials of improved and multivalent vaccines and therapeutic (oncolytic) viruses are ongoing.

HIV-1 vaccines: the search continues

This article gives an overview about the development of an HIV-1 vaccine. Tremendous numbers of papers have been published on this topic during the last 10 years, and this article can only touch on the different directions taken toward the development of an HIV-1 vaccine, and not give a complete overview of the entire field.

A region of the C-terminal tail of the gp41 envelope glycoprotein of human immunodeficiency virus type 1 contains a neutralizing epitope: evidence for its exposure on the surface of the virion

The approximately 150 amino acid C-terminal tail of the gp41 transmembrane glycoprotein of human immunodeficiency virus type 1 (HIV-1) is generally thought to be located inside the virion. However, we show here that both monoclonal IgG and polyclonal epitope-purified IgG specific for the (746)ERDRD(750) epitope that lies within the C-terminal tail neutralized infectious virus. IgG was mapped to the C-terminal tail by its failure to neutralize tail-deleted virus, and by sequencing of antibody-escape mutants. The fact that antibody does not cross lipid membranes, and infectious virus is by definition intact, suggested that ERDRD was exposed on the surface of the virion. This was confirmed by reacting virus and IgG, separating virus and unbound IgG by centrifugation, and showing that virus was neutralized to essentially the same extent as virus that had been in constant contact with antibody. Epitope exposure on virions was independent of temperature and therefore constitutive. Monoclonal antibodies specific to epitopes PDRPEG and IEEE, upstream of ERDRD, also bound to virions, suggesting that they too were located externally. Protease digestion destroyed the ERDRD and PDRPEG epitopes, consistent with their proposed external location. Altogether these data are consistent with part of the C-terminal tail of gp41 being exposed on the outside of the virion. Possible models of the structure of the gp41 tail, taking these observations into account, are discussed.

An evaluation of the genetic stability and pathogenicity of the Russian cold-adapted influenza A donor strains A/Leningrad/134/17/57 and A/Leningrad/134/47/57 in ferrets

The influenza A components of live attenuated vaccines used in Russia have been prepared as reassortants of the cold-adapted (ca) H2N2 viruses, A/Leningrad/134/17/57-ca (Len/17) and A/Leningrad/134/47/57-ca (Len/47), and virulent epidemic strains. The lesions responsible for attenuation within the six internal genes of each donor strain have been sequenced and described, but relatively little is known as to their stability before and after passage in susceptible hosts. In the work reported in this paper, RT-PCR restriction analysis and limited sequencing of individual genes were used to evaluate the stability of lesions in stocks of the both donor strains after passage in ferrets, which have been used widely as susceptible hosts for assessment of the virulence of influenza strains. Len/47 was shown to possess expected lesions by RT-PCR and restriction analysis. Substitution at position 1066 of the NP gene, which has been previously reported to be unique to Len/47 [Klimov et al., Virology 186 (1992) 795], was also shown to be present in all clones of Len/17. This change was confirmed by limited sequence analysis and was shown to be retained in progeny viruses isolated from the lungs and turbinates of inoculated ferrets. Two other changes in the PB2 and PB1 genes that were present in Len/47 were detected by limited sequence analysis alone. Further previously unreported minor changes were shown to be present for Len/17 and Len/47, but not both, and their significance is unknown. Limited replication of each donor strain occurred in ferrets and minimal clinical signs and histopathology were present. By contrast, the parental strain Len/57 and the recent epidemic strain A/Sydney/6/97 induced clinical signs and histopathology that were typical of influenza disease.

Lipopeptide vaccines--yesterday, today, and tomorrow

Peptide-based vaccines offer several potential advantages over the conventional whole proteins (or whole gene, in the case of genetic immunisation) in terms of purity and a high specificity in eliciting immune responses. However, concerns about toxic adjuvants, which are critical for immunogenicity of synthetic peptides, still remain. Lipopeptides, a form of peptide vaccine, discovered more then a decade ago, are currently under intensive investigation because they can generate comprehensive immune responses, without the use of adjuvants. In this review, we address the past of lipopeptide vaccines, highlight the progress made toward their optimisation, and stress future challenges and issues related to their synthesis, formulation, and delivery. In particular, the recent development of mucosal application of lipopeptide vaccines may present an ideal strategy against many pathogens that infect mucosal surfaces.

A pH-sensitive polymer that enhances cationic lipid-mediated gene transfer

The efficient release of nonviral gene carriers from endosomes is an important step for the successful delivery of DNA into the cell nucleus. A synthetic pH-sensitive anionic polymer, poly(propylacrylic acid) (PPAA), was designed to aid in endosomal escape of nonviral vectors and improve the transfection efficiencies with these vectors. Transfection of NIH3T3 fibroblasts with ternary physical mixtures of the cationic lipid DOTAP, pCMVbeta plasmid DNA, and PPAA showed marked enhancement of both gene expression levels and fraction of cells transfected compared to binary control mixtures of DOTAP and DNA. PPAA also significantly improved the serum-stability of DOTAP/DNA vectors. The DOTAP/DNA/PPAA vectors maintained high levels of transfection in media containing up to 50% serum. The striking enhancement of transfection efficiency with cationic lipid/DNA/PPAA mixtures, along with the enhanced serum-stability, suggests that PPAA may provide significant improvements for the in vivo intracellular delivery of drugs such as DNA, oligonucleotides, proteins, and peptides.

Properties of a neutralizing antibody that recognizes a conformational form of epitope ERDRD in the gp41 C-terminal tail of human immunodeficiency virus type 1

The possibility that epitopes from the C-terminal tail of the gp41 transmembrane protein of human immunodeficiency virus type 1 (HIV-1) are exposed the surface of the virion has long been contentious. Resolution of this has been hampered by the absence of any neutralizing monoclonal antibodies, but we have recently epitope-purified a neutralizing polyclonal IgG specific for one of the putative gp41 tail epitopes, (746)ERDRD(750). This was obtained from mice immunized parenterally with a plant virus chimera expressing residues 731-752 from the gp41 tail. The ERDRD epitope is highly conformational and is conserved in 81% of B clade viruses. Here, it is shown that this polyclonal ERDRD-specific IgG is highly potent, with an affinity of 2.2x10(8) M(-1), and a neutralization rate constant (-K(neut)) of 7.8x10(4) M(-1) s(-1) that exceeds that of nearly all other known HIV-1-neutralizing antibodies. ERDRD-specific IgG gave 50% neutralization at 0.1-0.2 microg/ml and 90% neutralization at approximately 3 microg/ml. It also neutralized virus that was already attached to target cells, and this and other data suggest that it neutralized by inhibiting a virion event that precedes the fusion-entry process. Consistent with this conclusion was the finding that neutralizing amounts of ERDRD-specific IgG did not inhibit the attachment of free virus to target cells. ERDRD-specific IgG was also cross-reactive and neutralized all but one of six B clade T cell line-adapted strains tested.

Immunogenic and antigenic dominance of a nonneutralizing epitope over a highly conserved neutralizing epitope in the gp41 envelope glycoprotein of human immunodeficiency virus type 1: its deletion leads to a strong neutralizing response

The Kennedy peptide, (731)PRGPDRPEGIEEEGGERDRDRS(752), from the cytoplasmic domain of the gp41 transmembrane envelope glycoprotein of HIV-1 contains a conformationally dependent neutralizing epitope (ERDRD) and a linear nonneutralizing epitope (IEEE). No recognized murine T cell epitope is present. The peptide usually stimulates virus-specific antibody, but this is not always neutralizing. Here we show that IEEE (or possibly IEEE plus adjacent sequence) is immunogenically and antigenically dominant over the ERDRD neutralizing epitope. Thus rabbits immunized in a variety of routes, doses, and adjuvants with a chimeric cowpea mosaic virus (CPMV) expressing the Kennedy peptide on its surface (CPMV-HIV/1) synthesized IEEE-specific serum antibody but no ERDRD-specific or HIV-1-neutralizing antibody. To test if this resulted from immunodominance or from a hole in the antibody repertoire, we immunized rabbits with chimera CPMV-HIV/29, which expresses the GERDRDR part of the Kennedy sequence. This chimera readily stimulated ERDRD-specific, neutralizing antibody. In mice the situation was less extreme, but individual animals with low neutralizing titers had a high ratio of IEEE-specific:ERDRD-specific antibody. Data are consistent with immunodominance of IEEE over ERDRD in the Kennedy peptide. IEEE-specific antibody was also antigenically dominant and prevented ERDRD-specific antibody from binding to its epitope and from neutralizing HIV-1. It may be that HIV-1 has evolved a nonneutralizing immunodominant epitope that allows it to possess a neutralizing epitope without suffering the consequences, and this idea is supported by the covariance of both epitope sequences. To our knowledge this is the first example of a defined sequence that controls the activity of an adjacent epitope.

Characterization of immune responses to experimental polyvalent subunit vaccines assembled in iscoms

Immune responses to experimental polyvalent subunit vaccines assembled in a particulate adjuvant/delivery system, iscoms, are described. The fusion protein ZZ-M5 comprises structures of staphylococcal protein A (ZZ) and the Plasmodium falciparum malaria antigen Pf155/RESA (M5). MHC congenic mice were immunized with ZZ-M5 conjugated to iscoms containing human influenza virus antigen (flu ag, M5-flu-isc) or to iscom matrix (iscom particles without flu ag, M5-isc). Comparison of antibody and T-cell responses to M5-isc and M5-flu-isc demonstrated that the flu ag in M5-flu-isc exhibits carrier-related helper functions and that the assembly of immunogens in M5-flu-isc did not result in any apparent antigenic competition. In addition, assembly of ZZ-M5 and flu ag in iscoms induced an alteration of the IgG subclass profile of the antibody response to M5. The results suggest that assembly of immunogens in iscoms may be a useful approach to the design of subunit vaccines but that both quantitative and qualitative aspects of the immunogenic properties of such constructs should be scrutinized.

Expression and immunogenicity of V3 loop epitopes of HIV-1, isolates SC and WMJ2, inserted in Salmonella flagellin

Synthetic oligonucleotides corresponding to specific V3 loop portions of two HIV-1 isolates, SC and WMJ2, were expressed in the flagella of a Salmonella live-vaccine strain. Expression of the inserted epitopes in flagellin and their exposure at the surface of flagellar filaments were shown by immunoblotting and immunogold labeling with anti-flagellin (Salmonella d) and anti-HIV-1(IIIB) V3 loop peptide sera. Live recombinant Salmonella strains expressing either one of the two V3 loop inserts were administered intraperitoneally to BALB/c mice. All these animals developed antibodies specific for the heterologous glycoprotein 120 (gp120) of HIV-1 MN strain, as detected by enzyme-linked immunosorbent assays (ELISA), two of the sera had neutralizing activity against the heterologous HIV-1 MN strain. Moreover, oral administration of the live Salmonella recombinant strains to mice evoked specific IgA directed against gp120.

Design of peptide and polypeptide vaccines

Advances have been made in the development of vaccines based on synthetic peptides and polypeptides representing tumor-associated antigens and protective epitopes of viruses and parasites. Advances within the past year include the design of vaccines based on artificial proteins, for example multiantigen peptides, branched polypeptides, fusion and recombinant peptides, as well as single T cell epitopes and tumor antigen peptides. Although peptide vaccines are not in use as yet, their potential is being explored.

Lipopeptide immunization without adjuvant induces potent and long-lasting B, T helper, and cytotoxic T lymphocyte responses against a malaria liver stage antigen in mice and chimpanzees

We have employed a 26-amino-acid synthetic peptide based on Plasmodium falciparum liver stage antigen-3 to evaluate improvements in immunogenicity mediated by the inclusion of a simple lipid-conjugated amino acid during peptide synthesis. Comparative immunization by the peptide in Freund's adjuvant or by the lipopeptide in saline shows that the addition of a palmitoyl chain can dramatically increase T helper (Th) cell responses in a wide range of major histocompatibility complex (MHC) class II haplotypes, to the extent that responses were induced in mice otherwise unable to respond to the non-modified peptide injected with Freund's adjuvant, and that the increased immunogenicity of the lipopeptide led to high and longer lasting antibody production (studied up to 8 months). B and T cell responses induced by the lipopeptide were reactive with native parasite protein epitopes, and a lipopeptide longer than ten amino acids was endogenously processed to associate with MHC class I and elicit cytotoxic T lymphocyte (CTL) responses. Finally, the lipopeptide was safe and highly immunogenic in chimpanzees, whose immune system is very similar to that of humans. Our results suggest that relatively large synthetic peptides, carefully chosen from pertinent areas of proteins and incorporating a simple palmitoyl-lysine, can induce not only CTL, but also strong Th and antibody responses in genetically diverse populations. Lipopeptides engineered in this way are simple to produce and purify under GMP conditions, they are well tolerated by apes, and with the enhanced immunogenicity without the need for adjuvant that we report here, they offer a quick and relatively low-cost route to provide material for human malaria vaccination trials.