Double conjugation strategy to incorporate lipid adjuvants into multiantigenic vaccines

A Comprehensive View of the Cancer-Immunity Cycle (CIC) in HPV-Mediated Cervical Cancer and Prospects for Emerging Therapeutic Opportunities

Cervical cancer (CC) is the fourth most common cancer in women worldwide, with more than 500,000 new cases each year and a mortality rate of around 55%. Over 80% of these deaths occur in developing countries. The most important risk factor for CC is persistent infection by a sexually transmitted virus, the human papillomavirus (HPV). Conventional treatments to eradicate this type of cancer are accompanied by high rates of resistance and a large number of side effects. Hence, it is crucial to devise novel effective therapeutic strategies. In recent years, an increasing number of studies have aimed to develop immunotherapeutic methods for treating cancer. However, these strategies have not proven to be effective enough to combat CC. This means there is a need to investigate immune molecular targets. An adaptive immune response against cancer has been described in seven key stages or steps defined as the cancer-immunity cycle (CIC). The CIC begins with the release of antigens by tumor cells and ends with their destruction by cytotoxic T-cells. In this paper, we discuss several molecular alterations found in each stage of the CIC of CC. In addition, we analyze the evidence discovered, the molecular mechanisms and their relationship with variables such as histological subtype and HPV infection, as well as their potential impact for adopting novel immunotherapeutic approaches.

Liposomal Formulations of a Polyleucine-Antigen Conjugate as Therapeutic Vaccines against Cervical Cancer

Human papilloma virus (HPV) is responsible for all cases of cervical cancer. While prophylactic vaccines are available, the development of peptide-based vaccines as a therapeutic strategy is still under investigation. In comparison with the traditional and currently used treatment strategies of chemotherapy and surgery, vaccination against HPV is a promising therapeutic option with fewer side effects. A peptide derived from the HPV-16 E7 protein, called 8Qm, in combination with adjuvants showed promise as a therapeutic vaccine. Here, the ability of polymerized natural amino acids to act as a self-adjuvating delivery system as a therapeutic vaccine was investigated for the first time. Thus, 8Qm was conjugated to polyleucine by standard solid-phase peptide synthesis and self-assembled into nanoparticles or incorporated in liposomes. The liposome bearing the 8Qm conjugate significantly increased mice survival and decreased tumor growth after a single immunization. Further, these liposomes eradicated seven-day-old well-established tumors in mice. Dendritic cell (DC)-targeting moieties were introduced to further enhance vaccine efficacy, and the newly designed liposomal vaccine was tested in mice bearing 11-day-old tumors. Interestingly, these DCs-targeting moieties did not significantly improve vaccine efficacy, whereas the simple liposomal formulation of 8Qm-polyleucine conjugate was still effective in tumor eradication. In summary, a peptide-based anticancer vaccine was developed that stimulated strong cellular immune responses without the help of a classical adjuvant.

Exploring bioactive peptides as potential therapeutic and biotechnology treasures: A contemporary perspective

In preceding years, bioactive peptides (BAPs) have piqued escalating attention owing to their multitudinous biological features. To date, many potential BAPs exhibiting anti-cancer activities have been documented; yet, obstacles such as their safety profiles and consumer acceptance continue to exist. Moreover, BAPs have been discovered to facilitate the suppression of Coronavirus Disease 2019 (CoVID-19) and maybe ideal for treating the CoVID-19 infection, as stated by published experimental findings, but their widespread knowledge is scarce. Likewise, there is a cornucopia of BAPs possessing neuroprotective effects that mend neurodegenerative diseases (NDs) by regulating gut microbiota, but they remain a subject of research interest. Additionally, a plethora of researchers have attempted next-generation approaches based on BAPs, but they need scientific attention. The text format of this critical review is organized around an overview of BAPs' versatility and diverse bio functionalities with emphasis on recent developments and novelties. The review is alienated into independent sections, which are related to either BAPs based disease management strategies or next-generation BAPs based approaches. BAPs based anti-cancer, anti-CoVID-19, and neuroprotective strategies have been explored, which may offer insights that could help the researchers and industries to find an alternate regimen against the three aforementioned fatal diseases. To the best of our knowledge, this is the first review that has systematically discussed the next-generation approaches in BAP research. Furthermore, it can be concluded that the BAPs may be optimal for the management of cancer, CoVID-19, and NDs; nevertheless, experimental and preclinical studies are crucial to validate their therapeutic benefits.

Peptide-Based Nanovaccines in the Treatment of Cervical Cancer: A Review of Recent Advances

Persistent infection with high-risk human papillomaviruses (HPVs), such as HPV-16 and HPV-18, can induce cervical cancer in humans. The disease carries high morbidity and mortality among females worldwide. Inoculation with prophylactic HPV vaccines, such as Gardasil^® or Cervarix^®, is the predominant method of preventing cervical cancer in females 6 to 26 years of age. However, despite the availability of commercial prophylactic HPV vaccines, no therapeutic HPV vaccines to eliminate existing HPV infections have been approved. Peptide-based vaccines, which form one of the most potent vaccine platforms, have been broadly investigated to overcome this shortcoming. Peptide-based vaccines are especially effective in inducing cellular immune responses and eradicating tumor cells when combined with nanoscale adjuvant particles and delivery systems. This review summarizes progress in the development of peptide-based nanovaccines against HPV infection.

Recent progress in synthetic self-adjuvanting vaccine development

Vaccination is a proven way to protect individuals against many infectious diseases, as currently highlighted in the global COVID-19 pandemic. Peptides- or small molecule antigen-based vaccination offer advantages over the...

Physical mixture of a cyclic lipopeptide vaccine induced high titres of opsonic IgG antibodies against group A streptococcus

Untreated or reoccurring group A Streptococcus (GAS) infection can lead to a number of post-infection complications, including rheumatic heart disease. There is no licenced vaccine for the treatment or prevention of GAS infection. We identified that a cyclic decapeptide plays a significant positive influence on the adjuvant activity of several lipid-antigen mixtures. Here, three synthetic vaccine components were synthesised: (1) J8-PADRE represents the GAS B cell antigen (J8) conjugated to the universal T helper epitope (PADRE); (2) a synthetic toll like receptor 2 (TLR2) ligand based on a C16 alkyl chain lipid moiety; and (3) a cyclic carrier deca-peptide. Previously, through structure-immune activity investigations, it was observed that a physical mixture of these three components had significantly higher IgG immune responses when compared to a fully conjugated vaccine construct. Expanding the scope of this structure-activity investigation, we show that the presence of the cyclic peptide is required for the induction of a strong, balanced Th1/Th2 immune response when compared with lipid and antigen only, and cyclic lipopeptide plus B/T cell antigen physical mixtures.

Poly(hydrophobic amino acid) Conjugates for the Delivery of Multiepitope Vaccine against Group A Streptococcus

Peptide-based vaccines are composed of small, defined, antigenic peptide epitopes. They are designed to induce well-controlled immune responses. Multiple epitopes are often employed in these vaccines to cover strain variability of a pathogen. However, peptide epitopes cannot stimulate adequate immune responses on their own and require an adjuvant (immune stimulant) and/or delivery system. Here, we designed and synthesized a multiepitope vaccine candidate against Group A Streptococcus (GAS) composed of several B-cell epitopes (J8, PL1, and 88/30) derived from GAS M-protein, universal PADRE T-helper cell epitope, and a polyleucine self-adjuvanting unit. The vaccine components were conjugated together (using mercapto-maleimide and azide-alkyne Huisgen cycloaddition reactions) or delivered as a mixture. The conjugated multiepitope vaccine candidate self-assembled into small nanoparticles and chain-like aggregated nanoparticles (CLANs) that were able to induce the production of J8-, PL1-, and 88/30-specific antibodies in mice. The multiepitope conjugate and the physical mixture of conjugates bearing the individual epitopes produced similar nanoparticles and induced comparable immune responses. Hence, simple physical mixing can replace complex chemical conjugation to produce multiepitope nanoparticles with equivalent morphology and immunological efficacy. This greatly simplifies vaccine production.

Chemical Conjugation Strategies for the Development of Protein-Based Subunit Nanovaccines

The production of subunit nanovaccines relies heavily on the development of a vaccine delivery system that is safe and efficient at delivering antigens to the target site. Nanoparticles have been extensively investigated for vaccine delivery over the years, as they often possess self-adjuvanting properties. The conjugation of antigens to nanoparticles by covalent bonds ensures co-delivery of these components to the same subset of immune cells in order to trigger the desired immune responses. Herein, we review covalent conjugation strategies for grafting protein or peptide antigens onto other molecules or nanoparticles to obtain subunit nanovaccines. We also discuss the advantages of chemical conjugation in developing these vaccines.

Manganese-Doped Silica-Based Nanoparticles Promote the Efficacy of Antigen-Specific Immunotherapy

Prophylactic human papillomavirus (HPV) vaccines are commercially available for prevention of infection with cancerogenic HPV genotypes but are not able to combat pre-existing HPV-associated disease. In this study, we designed a nanomaterial-based therapeutic HPV vaccine, comprising manganese (Mn⁴⁺)-doped silica nanoparticles (Mn⁴⁺-SNPs) and the viral neoantigen peptide GF001 derived from the HPV16 E7 oncoprotein. We show in mice that Mn⁴⁺-SNPs act as self-adjuvants by activating the inflammatory signaling pathway via generation of reactive oxygen species, resulting in immune cell recruitment to the immunization site and dendritic cell maturation. Mn⁴⁺-SNPs further serve as Ag carriers by facilitating endo/lysosomal escape via depletion of protons in acidic endocytic compartments and subsequent Ag delivery to the cytosol for cross-presentation. The Mn⁴⁺-SNPs+GF001 nanovaccine induced strong E7-specific CD8⁺ T cell responses, leading to remission of established murine HPV16 E7-expressing solid TC-1 tumors and E7-expressing transgenic skin grafts. This vaccine construct offers a simple and general strategy for therapeutic HPV and potentially other cancer vaccines.

Double Conjugation Using Mercapto-Acryloyl and Alkyne-Azide Reactions for the Synthesis of Branched Multiantigenic Vaccine Candidates

Chemical conjugation of peptide epitopes and lipids into a single branched lipopeptide is a promising strategy for the generation of multiantigenic vaccines. We developed a double conjugation strategy that utilizes a mercapto-acryloyl Michael addition reaction between two unprotected peptides, followed by a copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) click reaction. The technique proved capable of producing branched multiantigenic vaccine candidates with an overall yield of 78%.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Lipids as Activators of Innate Immunity in Peptide Vaccine Delivery

BACKGROUND

Innate immune system plays an important role in pathogen detection and the recognition of vaccines, mainly through pattern recognition receptors (PRRs) that identify pathogen components (danger signals). One of the typically recognised bacterial components are lipids in conjugation with peptides, proteins and saccharides. Lipidic compounds are readily recognised by the immune system, and thus are ideal candidates for peptide- based vaccine delivery. Thus, bacterial or synthetic lipids mixed with, or conjugated to, antigens have shown adjuvant properties. These systems have many advantages over traditional adjuvants, including low toxicity and good efficacy for stimulating mucosal and systemic immune responses.

METHODS

The most recent literature on the role of lipids in stimulation of immune responses was selected for this review. The vast majority of reviewed papers were published in the last decade. Older but significant findings are also cited.

RESULTS

This review focuses on the development of lipopeptide vaccine systems including application of palmitic acid, bacterial lipopeptides, glycolipids and the lipid core peptide and their routes of administration. The use of liposomes as a delivery system that incorporates lipopeptides is discussed. The review also includes a brief description of immune system in relation to vaccinology and discussion on vaccine delivery routes.

CONCLUSION

Lipids and their conjugates are an ideal frontrunner in the development of safe and efficient vaccines for different immunisation routes.

Protein and Peptide Biomaterials for Engineered Subunit Vaccines and Immunotherapeutic Applications

Although vaccines have been the primary defense against widespread infectious disease for decades, there is a critical need for improvement to combat complex and variable diseases. More control and specificity over the immune response can be achieved by using only subunit components in vaccines. However, these often lack sufficient immunogenicity to fully protect, and conjugation or carrier materials are required. A variety of protein and peptide biomaterials have improved effectiveness and delivery of subunit vaccines for infectious, cancer, and autoimmune diseases. They are biodegradable and have control over both material structure and immune function. Many of these materials are built from naturally occurring self-assembling proteins, which have been engineered for incorporation of vaccine components. In contrast, others are de novo designs of structures with immune function. In this review, protein biomaterial design, engineering, and immune functionality as vaccines or immunotherapies are discussed.

Structure-activity relationship of group A streptococcus lipopeptide vaccine candidates in trimethyl chitosan-based self-adjuvanting delivery system

Synthetic peptide vaccines based on epitopes derived from the conserved region of M-protein are proving to be a realistic option for protection against group A streptococcus (GAS). However, peptide epitopes alone are poorly immunogenic due to lack of pathogen-associated structural patterns. Therefore, we developed a GAS peptide vaccine based on combined lipidic TLR 2 agonist and self-adjuvanting polymers. We synthesized three α-poly-l-glutamic acid (PGA) conjugated lipopeptides composed of 2-amino-d,l-hexadecanoic acid, GAS B-cell peptide epitope J8 (QAEDKVKQSREAKKQVEKALKQLEDKVQ) and universal T-helper epitope PADRE (AKFVAAWTLKAAA) in different spatial arrangements. The anionic lipopeptide conjugates formed nanoparticles via ionic-complexation with a cationic polymer, trimethyl chitosan (TMC). We demonstrated that the spatial arrangement of vaccine components has a significant influence on peptide conformation and particle formation and, as such, contributes to the differential efficacy and opsonin-mediated killing potential of nanovaccines. Nanoparticles carrying branched helical lipopeptide with T-helper epitope on free N-termini (NP3) stimulated the most potent humoral immune responses. Lipopeptides without TMC (LP1-LP3) and TMC nanoparticles of peptide alone (without lipid) NP (P1) were poor inducers of antibody production, indicating that both TMC and lipid are required to induce a strong opsonic immune response.

Liposomal formulation of polyacrylate-peptide conjugate as a new vaccine candidate against cervical cancer

Peptide-based vaccines have been proposed as a therapeutic strategy for many infectious diseases, including human papilloma virus (HPV)-related cervical cancer. Peptide-based vaccines are a better treatment option than traditional chemotherapeutic agents and surgery, as they rely on the use of the body’s immune system to fight cancer cells, resulting in minimal risk of side effects. However, to increase the efficacy of peptide-based vaccines, the application of potent adjuvant and a suitable delivery system is essential. In this study, we developed a self-adjuvanting delivery system based on a combination of polymer and liposomes, for a therapeutic vaccine against cervical cancer. Peptide epitope (8Qm) derived from HPV-16 E7 protein was conjugated to dendritic poly(tert-butyl acrylate) as a primary delivery system and incorporated into cationic liposomes, which served as a secondary delivery system. Our vaccine candidate was able to kill established HPV-16 E7-positive tumor (TC-1) cells in mice following a single immunization. The immunized mice had 80% survival rate after two months. In contrast, both polymer-8Qm conjugate and liposomes bearing 8Qm failed to eradicate TC-1 tumors. The survival rate of mice was only 20% when immunized with 8Qm formulated with standard incomplete Freund’s adjuvant.

Induction of high titred, non-neutralising antibodies by self-adjuvanting peptide epitopes derived from the respiratory syncytial virus fusion protein

Respiratory syncytial virus (RSV) causes severe lower respiratory tract illness in infants and young children. The significant morbidity and mortality rates associated with RSV infection make an effective RSV vaccine development a priority. Two neutralising antibody binding sites, Ø and II, located on the pre-fusion RSV F glycoprotein are prime candidates for epitope-focused vaccine design. We report on a vaccine strategy that utilises a lipid core peptide (LCP) delivery system with self-adjuvanting properties in conjunction with either the antigenic site Ø or II (B cell epitopes) along with PADRE as a T helper cell epitope. These LCP constructs adopted the desired helical conformation in solution and were recognised by their cognate antibodies D25 and Motavizumab, specific for site Ø and II on RSV F protein, respectively. The LCP constructs were capable of eliciting higher levels of antigen specific antibodies than those induced by antigens administered with complete Freund's adjuvant, demonstrating the potent adjuvanting properties of LCP delivery. However, the antibodies induced failed to recognise native F protein or neutralise virus infectivity. These results provide a note of caution in assuming that peptide vaccines, successfully designed to structurally mimic minimal linear B cell epitopes, will necessarily elicit the desired immune response.

The application of self-assembled nanostructures in peptide-based subunit vaccine development

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Smaller polymer-peptide conjugates-based nanoparticles are often more immunogenic.

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Lipid-antigen conjugates-based nanoparticles can interact with immune receptors.

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Peptides with β-sheet conformation usually form nanofibers.

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α-Helical and random coil peptides tend to self-assemble into nanoparticles.

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Peptide-based nanostructures are usually poorer inducers of immune responses.

Peptide based-vaccines are becoming one of the most widely investigated prophylactic and therapeutic health care interventions against a variety of diseases, including cancer. However, the lack of a safe and highly efficient adjuvant (immune stimulant) is regarded as the biggest obstacle to vaccine development. The incorporation of a peptide antigen in a nanostructure-based delivery system was recently shown to overcome this obstacle. Nanostructures are often formed from antigens conjugated to molecules such as polymers, lipids, and peptide, with the help of self-assembly phenomenon. This review describes the application of self-assembly process for the production of peptide-based vaccine candidates and the ability of these nanostructures to stimulate humoral and cellular immune responses.

Comparison of Fluorinated and Nonfluorinated Lipids in Self-Adjuvanting Delivery Systems for Peptide-Based Vaccines

Safe immunostimulants (adjuvants) are essential for the development of highly potent peptide-based vaccines. This study examined for the first time whether fluorinated lipids could stimulate humoral immunity in vivo when conjugated to peptide antigen. The impact of fluorination on humoral immunity was tested using a library of peptide-based vaccine candidates against the group A streptococcus (GAS). The fluorinated constructs stimulated similar mouse IgG titers to those elicited by complete Freund's adjuvant (CFA) and were higher than those produced in mice that received the nonfluorinated constructs.

Synthesis of Multicomponent Peptide-Based Vaccine Candidates against Group A Streptococcus

Group A streptococcus (GAS; Streptococcus pyogenes), known as the ‘flesh-eating bacterium’, is a human bacterial pathogen that normally causes benign infections (e.g. sore throat and pyoderma), but is also responsible for severe invasive infections (e.g. ‘flesh-eating’ disease and toxic shock syndrome), heart disease, and kidney failure. A safe commercial GAS vaccine is yet to be developed. Individual GAS antigens demonstrate potential universal expression across all GAS serotypes (>200 known), with dramatically reduced concern for autoimmune complications, and compelling efficacy in preclinical testing in mice. In this study, we developed a stepwise conjugation strategy, copper-catalysed alkyne–azide cycloaddition reaction (CuAAC), followed by mercapto–maleimide conjugation, to synthesise a multiantigenic, self-adjuvanting, peptide-based vaccine candidate against GAS. This multiantigenic vaccine includes two GAS antigens, J8 and NS1, a T-helper epitope, PADRE, and a self-adjuvanting moiety, dipalmitoyl serine.