Single-chain lipopeptide vaccines for the induction of virus-specific cytotoxic T cell responses in randomly selected populations

Lipopeptides for Vaccine Development

The development of lipopeptides (lipidated peptides) for vaccines is discussed, including their role as antigens and/or adjuvants. Distinct classes of lipopeptide architectures are covered including simple linear and ligated constructs and lipid core peptides. The design, synthesis, and immunological responses of the important class of glycerol-based Toll-like receptor agonist lipopeptides such as Pam₃CSK₄, which contains three palmitoyl chains and a CSK₄ hexapeptide sequence, and many derivatives of this model immunogenic compound are also reviewed. Self-assembled lipopeptide structures including spherical and worm-like micelles that have been shown to act as vaccine agents are also described. The work discussed includes examples of lipopeptides developed with model antigens, as well as for immunotherapies to treat many infectious diseases including malaria, influenza, hepatitis, COVID-19, and many others, as well as cancer immunotherapies. Some of these have proceeded to clinical development. The research discussed highlights the huge potential of, and diversity of roles for, lipopeptides in contemporary and future vaccine development.

Palmitoylated antigens for the induction of anti-tumor CD8+ T cells and enhanced tumor recognition

Induction of tumor-specific cytotoxic CD8⁺ T cells (CTLs) via immunization relies on the presentation of tumor-associated peptides in major histocompatibility complex (MHC) class I molecules by dendritic cells (DCs). To achieve presentation of exogenous peptides into MHC class I, cytosolic processing and cross-presentation are required. Vaccination strategies aiming to induce tumor-specific CD8⁺ T cells via this exogenous route therefore pose a challenge. In this study, we describe improved CD8⁺ T cell induction and in vivo tumor suppression of mono-palmitic acid-modified (C16:0) antigenic peptides, which can be attributed to their unique processing route, efficient receptor-independent integration within lipid bilayers, and continuous intracellular accumulation and presentation through MHC class I. We propose that this membrane-integrating feature of palmitoylated peptides can be exploited as a tool for quick and efficient antigen enrichment and MHC class I loading. Importantly, both DCs and non-professional antigen-presenting cells (APCs), similar to tumor cells, facilitate anti-tumor immunity by efficient CTL priming via DCs and effective recognition of tumors through enhanced presentation of antigens.

Development of an epitope-based HIV-1 vaccine strategy from HIV-1 lipopeptide to dendritic-based vaccines

INTRODUCTION

Development of a safe, effective and globally affordable Human Immunodeficiency Virus strain 1 (HIV-1) vaccine offers the best hope for future control of the HIV-1 pandemic. However, with the exception of the recent RV144 trial, which elicited a modest level of protection against infection, no vaccine candidate has shown efficacy in preventing HIV-1 infection or in controlling virus replication in humans. There is also a great need for a successful immunotherapeutic vaccine since combination antiretroviral therapy (cART) does not eliminate the reservoir of HIV-infected cells. But to date, no vaccine candidate has proven to significantly alter the natural history of an individual with HIV-1 infection. Areas covered: For over 25 years, the ANRS (France Recherche Nord&Sud Sida-HIV hépatites) has been committed to an original program combining basic science and clinical research developing an epitope-based vaccine strategy to induce a multiepitopic cellular response against HIV-1. This review describes the evolution of concepts, based on strategies using HIV-1 lipopeptides towards the use of dendritic cell (DC) manipulation. Expert commentary: Understanding the crucial role of DCs in immune responses allowed moving from the non-specific administration of HIV-1 sequences with lipopeptides to DC-based vaccines. These DC-targeting strategies should improve HIV-1 vaccine efficacy.

Self-adjuvanting vaccine against group A streptococcus: application of fibrillized peptide and immunostimulatory lipid as adjuvant

Peptides are of great interest to be used as vaccine antigens due to their safety, ease of manufacturing and specificity in generating immune response. There have been massive discoveries of peptide antigens over the past decade. However, peptides alone are poorly immunogenic, which demand co-administration with strong adjuvant to enhance their immunogenicity. Recently, fibril-forming peptides such as Q11 and lipoamino acid-based carrier have been identified to induce substantial immune responses when covalently linked to peptide epitope. In this study, we have incorporated either Q11 or lipoamino acids to a peptide epitope (J14) derived from M protein of group A streptococcus to develop self-adjuvanting vaccines. J14, Q11 and lipoamino acids were also conjugated together in a single vaccine construct in an attempt to evaluate the synergy effect of combining multiple adjuvants. Physicochemical characterization demonstrated that the vaccine constructs folded differently and self-assembled into nanoparticles. Significantly, only vaccine constructs containing double copies of lipoamino acids (regardless in conjugation with Q11 or not) were capable to induce significant dendritic cells uptake and subsequent J14-specific antibody responses in non-sizes dependent manners. Q11 had minimal impact in enhancing the immunogenicity of J14 even when it was used in combination with lipoamino acids. These findings highlight the impact of lipoamino acids moiety as a promising immunostimulant carrier and its number of attachment to peptide epitope was found to have a profound effect on the vaccine immunogenicity.

Mucosal herpes immunity and immunopathology to ocular and genital herpes simplex virus infections

Herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) are amongst the most common human infectious viral pathogens capable of causing serious clinical diseases at every stage of life, from fatal disseminated disease in newborns to cold sores genital ulcerations and blinding eye disease. Primary mucocutaneous infection with HSV-1 & HSV-2 is followed by a lifelong viral latency in the sensory ganglia. In the majority of cases, herpes infections are clinically asymptomatic. However, in symptomatic individuals, the latent HSV can spontaneously and frequently reactivate, reinfecting the muco-cutaneous surfaces and causing painful recurrent diseases. The innate and adaptive mucosal immunities to herpes infections and disease remain to be fully characterized. The understanding of innate and adaptive immune mechanisms operating at muco-cutaneous surfaces is fundamental to the design of next-generation herpes vaccines. In this paper, the phenotypic and functional properties of innate and adaptive mucosal immune cells, their role in antiherpes immunity, and immunopathology are reviewed. The progress and limitations in developing a safe and efficient mucosal herpes vaccine are discussed.

Route of uptake of palmitoylated encephalitogenic peptides of myelin proteolipid protein by antigen-presenting cells: importance of the type of bond between lipid chain and peptide and relevance to autoimmunity

Previously, we have shown that thiopalmitoylation of peptides of myelin proteolipid protein, as occurs naturally in vivo, increases their ability to induce experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis, and skews the autoimmune response toward a CD4(+)-mediated response. In contrast, the same peptide, when synthesized with a stable amide bond between peptide and lipid, inhibits experimental autoimmune encephalomyelitis and skews the response toward a CD8(+) response. The aim of the current study was to determine the mechanisms responsible for these observations. We show that proteolipid protein lipopeptides, when synthesized with a thioester bond between the lipid and the peptide, are taken up into APCs via an actin-independent endocytic route, the thioester bond is cleaved in the endosome, and the peptide is subsequently displayed on the surface of the APC in the context of MHC class II. The same peptide, when synthesized with the lipid attached via a stable amide bond, rapidly enters into the cytoplasm of the APC and forms micelles; however, the bond between peptide and lipid is not cleaved, and the micelles travel via the endoplasmic reticulum to complex with MHC class I. These findings have implications for vaccine development and for the development of MHC class II-restricted autoimmune diseases, as many human autoantigens thus far identified are thioacylated.

Cytotoxic T lymphocyte response induced by an improved synthetic lipopeptide vaccine against cervical cancer

AIM

To explore cytotoxic T lymphocyte (CTL) response induced by the lipopeptide vaccine against cervical cancer.

METHODS

The immunological effect inducing CD8+ T cell-mediated cytotoxicity was investigated in human leukocyte antigen (HLA)-A2 transgenic mice and peripheral blood mononuclear cells (PBMC) of healthy HLA-A2.1+blood donor. The activity of specific CTL was measured by using a standard 4 h( 51)Cr release assay. The content of major histocompatibility complex (MHC) I on T2 cells and the expression of immune molecules on dendritic cells (DC) were detected by flow cytometry, and the concentrations of interleukin (IL)-12 and interferon-gamma were determined by ELISA.

RESULTS

The lipopeptide induced a strong epitope-specific CTL response both in vivo (transgenic mice) and in vitro (human PBMC). This CTL induction was critically dependent on the presence of the helper T lymphocyte epitope in transgenic mice, and the presence of a lipid tail bypassed the need for an adjuvant. The stability and persistence of the antigenic complex formed with the lipopeptide increased in comparison with the CTL parental peptide. The lipopeptide could induce the production of IL-12 in DC, but not the maturation of DC directly.

CONCLUSION

The combination of CTL and the T helper epitope and lipid molecule can remarkably improve the immunogenicity of the CTL peptide, the mechanism of which is associated with an increase in the stability and persistence of the antigenic complex formed with the lipopeptide and in the production of IL-12 in DC induced by the lipopeptide. The lipopeptide can be considered a more effective vaccine type for human being.

Method for the synthesis of highly pure vaccines using the lipid core peptide system

Traditional vaccines consisting of whole attenuated microorganisms, killed microorganisms, or microbial components, administered with an adjuvant (e.g. alum), have been proved to be extremely successful. However, to develop new vaccines, or to improve upon current vaccines, new vaccine development techniques are required. Peptide vaccines offer the capacity to administer only the minimal microbial components necessary to elicit appropriate immune responses, minimizing the risk of vaccination associated adverse effects, and focusing the immune response toward important antigens. Peptide vaccines, however, are generally poorly immunogenic, necessitating administration with powerful, and potentially toxic adjuvants. The attachment of lipids to peptide antigens has been demonstrated as a potentially safe method for adjuvanting peptide epitopes. The lipid core peptide (LCP) system, which incorporates a lipidic adjuvant, carrier, and peptide epitopes into a single molecular entity, has been demonstrated to boost immunogenicity of attached peptide epitopes without the need for additional adjuvants. The synthesis of LCP systems normally yields a product that cannot be purified to homogeneity. The current study describes the development of methods for the synthesis of highly pure LCP analogs using native chemical ligation. Because of the highly lipophilic nature of the LCP lipid adjuvant, difficulties (e.g. poor solubility) were experienced with the ligation reactions. The addition of organic solvents to the ligation buffer solubilized lipidic species, but did not result in successful ligation reactions. In comparison, the addition of approximately 1% (w/v) sodium dodecyl sulfate (SDS) proved successful, enabling the synthesis of two highly pure, tri-epitopic Streptococcus pyogenes LCP analogs. Subcutaneous immunization of B10.BR (H-2(k)) mice with one of these vaccines, without the addition of any adjuvant, elicited high levels of systemic IgG antibodies against each of the incorporated peptides.

Structure-based design of peptides that self-assemble into regular polyhedral nanoparticles

Artificial particulate systems such as polymeric beads and liposomes are being applied in drug delivery, drug targeting, antigen display, vaccination, and other technologies. Here we used computer modeling to design a novel type of nanoparticles composed of peptides as building blocks. We verified the computer models via solid-phase peptide synthesis and biophysical analyses. We describe the structure-based design of a novel type of nanoparticles with regular polyhedral symmetry and a diameter of about 16 nm, which self-assembles from single polypeptide chains. Each peptide chain is composed of two coiled coil oligomerization domains with different oligomerization states joined by a short linker segment. In aqueous solution the peptides form nanoparticles of about 16 nm diameter. Such peptide nanoparticles are ideally suited for medical applications such as drug targeting and drug delivery systems, such as imaging devices, or they may be used for repetitive antigen display.

An insect antibacterial peptide-based drug delivery system

The ability of the short, proline-rich native antibacterial peptides to penetrate bacterial and host cells suggests the utility of these transport systems in delivering peptidic cargo into cells. We studied the uptake of pyrrhocoricin and its most potent dimeric analogue by bacteria as well as human dendritic cells and fibroblasts. Native pyrrhocoricin entered the susceptible organism Escherichia coli very efficiently and the nonsusceptible bacterium Staphylococcus aureus to a significant degree. The antibacterial peptide also penetrated human monocyte-derived dendritic cells. It failed, however, to enter fibroblasts, whereas the designer analogue Pip-pyrr-MeArg dimer penetrated all the cell types that were studied. When glucoincretin hormone Glp-1 fragment 7-36 was cosynthesized with the dimer, the antibacterial peptide derivative lost its ability to cross the bacterial membrane layer. In contrast, a chimera of the Pip-pyrr-MeArg dimer and two copies of a shorter (nine residues) class I major histocompatibility complex epitope successfully entered bacterial and mammalian cells. While the Pip-pyrr-MeArg dimer was not immunogenic when inoculated into mice, the chimera elicited a strong cytotoxic T-cell response, indicating the maintenance of the antigenic integrity of the cargo in the peptide conjugate. The chimera when tested for its immunological properties activated human dendritic cells significantly more strongly than any of the two independent fragments alone, yet lacked mammalian cell toxicity. These results confirm the utility of designed pyrrhocoricin analogues for delivery of peptidic cargo across cell membranes in general, and their potential as carriers for epitope-based vaccines in particular.

Immunostimulants and Toll-like receptor ligands obtained by screening combinatorial lipopeptide collections*

Synthetic lipopeptides carrying the head group of bacterial lipoproteins are specific ligands of Toll-like receptors (TLR). The three fatty acids containing lipopeptides with the tripalmitoyl-S-glyceryl-cysteinyl N-terminus (Pam(3)Cys) are agonists of TLR2. The structurally related lipopeptides with a head group lacking the fatty acyl residue at the amino-terminus (Pam(2)Cys) stimulate TLR2 and 6. To investigate the influence of the peptide chain of lipohexapeptides with a free N-terminus with regard to their ability to enhance B-cell proliferation, a randomized S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteinyl-pentapeptide amide collection Pam(2)CysXXXXX and 5 x 19 subcollections (Pam(2)CysOXXXX, Pam(2)CysXOXXX, Pam(2)CysXXOXX, Pam(2)CysXXXOX, Pam(2)CysXXXXO, O: all protein amino acids except Cys) were prepared by parallel solid-phase synthesis. The collection represents synthetic lipopeptide analogues of the numerous bacterial lipoproteins and of mycoplasma lipoprotein. Each of the 95 subcollections is characterized by one defined and four degenerated amino acid positions thus comprising 19(4) individual lipopeptides with free N-terminal amino groups. High-performance liquid chromatography electrospray mass spectrometry (HPLC-ESI-MS) was applied for the analytical characterization of the lipohexapeptide amide subcollections and for the individual lipohexapeptide amides. The subcollections were tested for polyclonal activation of murine spleen cells, deconvolution led to highly active single S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteinyl-pentapeptide amides.

Epitope-based vaccines: an update on epitope identification, vaccine design and delivery

The basic premise of the epitope-based approach to vaccine development is that, in certain cases, the responses induced by the natural immunogen are not optimal, and can be improved upon by isolation or optimization of specific components of the response. For example, immunodominance is a key factor limiting the type and breadth of adaptive immunity. Recent advances in understanding the mechanisms of immunodominance thus represent an opportunity to further develop the epitope-based approach.

Coadministration of an interleukin-12 gene and a Trypanosoma cruzi gene improves vaccine efficacy

We tested the immunogenicity of two Trypanosoma cruzi antigens injected into mice in the form of DNA vaccine. Immunization with DNA encoding dihydroorotate dehydrogenase did not confer protective immunity in all mouse strains tested. Immunization with DNA encoding trans-sialidase surface antigen (TSSA) protected C57BL/6 (H-2(b)) mice but not BALB/c (H-2(d)) or C3H/Hej (H-2(k)) mice against lethal T. cruzi infection. In vivo depletion of CD4(+) or CD8(+) T cells abolished the protective immunity elicited by TSSA gene in C57BL/6 mice. Enzyme-linked immunospot assay with splenocytes from T. cruzi-infected mice or TSSA gene-vaccinated mice identified an H-2K(b)-restricted antigenic peptide, ANYNFTLV. The CD8(+)-T-cell line specific for this peptide could recognize T. cruzi-infected cells in vitro and could protect naive mice from lethal infection when adoptively transferred. Coadministration of the interleukin-12 (IL-12) gene with the TSSA gene facilitated the induction of ANYNFTLV-specific CD8(+) T cells and improved the vaccine efficacy against lethal T. cruzi infection. These results reinforced the utility of immunomodulatory adjuvants such as IL-12 gene for eliciting protective immunity against intracellular parasites by DNA vaccination.

Prospects for targeting the Bcl-2 family of proteins to develop novel cytotoxic drugs

Over the last decade the molecular mechanisms controlling programmed cell death (apoptosis) have become clearer. It appears that many physiological and damage signals activate the cell death machinery by inhibiting the pro-survival Bcl-2 proteins. Since many chemotherapeutic drugs used to treat cancers activate the cell death machinery indirectly, there is much interest in developing peptide and non-peptide mimics of the BH3-only proteins, a family of proteins that act as direct antagonists of Bcl-2, as novel anti-cancer agents. This commentary review current progress in our search for such drugs and discusses recent findings in light of our current understanding of the cell death signaling. The potential for discovering novel agents that may form a useful part of the treatment of malignant disease is enormous but we still lack critical understanding of precisely how Bcl-2 function. However, the frequency of mutations affecting proteins that (directly or indirectly) impinge on apoptosis suggests that the approach of targeting Bcl-2 might be a profitable one.

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.