Peptide vaccines and peptide libraries

Synthetic immunogens, containing built-in adjuvanticity, B cell, T helper cell and CTL epitopes or mimotopes, are ideal and invaluable tools to study the immune response with respect to antigen processing and presentation. This serves as a basis for the development of complete and minimal vaccines which do not need large carrier proteins, further adjuvants, liposome formulations or other delivery systems. Combinatorial peptide libraries, either completely random or characterized by one or several defined positions, are useful tools for the identification of the critical features of B cell epitopes and of MHC class I and class II binding natural and synthetic epitopes. The complete activity pattern of an O/Xn library with hundreds of peptide collections, each made up from billions of different peptides, represents the ranking of amino acid residues mediating contact to the target proteins of the immune system. Combinatorial libraries support the design of peptides applicable in vaccination against infectious agents as well as therapeutic tumour vaccines. Using the principle of lipopeptide vaccines, strong humoral and cellular immune responses could be elicited. The lipopeptide vaccines are heat-stable, non-toxic, fully biodegradable and can be prepared on the basis of minimized epitopes by modern methods of multiple peptide synthesis. The lipopeptides activate the antigen-presenting macrophages and B cells and have been recently shown to stimulate innate immunity by specific interaction with receptors of the Toll family.     

Synthetic Peptide-Based Vaccines Against Influenza

Advances have been made in the development of vaccines based on synthetic peptides representing protective epitopes of the influenza virus. The study reviewed here evaluates the capacity of three epitopes in different delivery systems to induce specific immune response and protect mice against viral challenge infection. Although peptide vaccines are not in use yet, they continue to be explored as is discussed herewith.     

Therapeutic vaccines against infectious diseases

Therapeutic vaccines against chronic infectious diseases aim at eliciting broad humoral and cellular immune responses against multiple target antigens. Importantly, the development of such vaccines will help to establish surrogate markers of protection in humans and thus will augment the subsequent development of efficient prophylactic vaccines. A combination of synthetic small-molecule drugs and immunotherapeutics is likely to represent a powerful means of controlling chronic infections in the future. Challenges faced in developing therapeutic vaccines include the following: first, overcoming the potential impairment of immune responses due to established infection; second, optimizing schedules of vaccine administration in combination with standard of care chemotherapy; and third, defining what biological and immunological read-outs should be used to infer vaccine efficacy.     

Recent Advances in Design and Synthesis of Self-Adjuvanting Lipopeptide Vaccines

Synthetic lipopeptide vaccines are being increasingly investigated mainly because of the advantages they offer over traditional vaccines, including safety of use in humans, high specificity in eliciting immune responses, greater purity and large scale/cost-effective production capacity. Moreover, a number of lipopeptide vaccines designed to possess self-adjuvanting properties have been developed and tested in vitro and in vivo. Producing high levels of serum-specific antibodies against incorporated peptide epitopes, they are showing their potential as effective vaccine candidates without the need for a co-administered adjuvant and/or carrier protein, often associated with undesirable effects in humans. This review presents recent insights on lipopeptide vaccine research and development, particularly on (1) the influence of the orientation of peptide epitopes and lipids on immune responses, (2) the use of carbohydrates for vaccine targeting, adjuvanting or as peptide epitope carriers, and (3) synthetic approaches to highly pure, multi-epitopic vaccine molecules using native chemical ligation techniques. Incorporation of different types of antigens within the same lipopeptide construct could provide a lipopeptide vaccine candidate suitable for safe and effective mucosal administration, which is a comfortable way of drug delivery.     

Defined synthetic vaccines

Although vaccines have proven very successful in preventing certain infectious diseases, progress in the field has been slowed by the tediousness of developing classical vaccines consisting of whole pathogens. Thus, there is great need for improvement in several areas: firstly, the range of diseases which can be treated has to be expanded. Secondly, antigens have to be defined to make the use of whole pathogens as antigen obsolete. And thirdly, new adjuvants have to be developed which show low toxicity, high potency and are also able to drive the immune response in the desired direction. Ideally, a vaccine would only consist of well-characterized, synthetic materials. This review summarizes the different approaches for the development of completely defined synthetic vaccines.     

Synthetic Peptide-Based Vaccines Against Influenza

Summary Advances have been made in the development of vaccines based on synthetic peptides representing protective epitopes of the influenza virus. The study reviewed here evaluates the capacity of three epitopes in different delivery systems to induce specific immune response and protect mice against viral challenge infection. Although peptide vaccines are not in use yet, they continue to be explored as is discussed herewith.     

Bioactive Fragment of Human IL-1β [163-171] Modulates the Immune Response to Synthetic Peptides of HIV

The activation of T helper cells specific for viral antigens is critical for antibody production and the generation of cytotoxic T cells during retroviral infection. In this study, we examined the effect of linking HIV peptides with a bioactive fragment of human interleukin-1β (IL-1β) (163–171) on the induction of immune response to the peptides. A panel of highly purified synthetic peptides representing defined regions of gp41, Gag and gp120 were used as antigens. Mouse spleen cells primed with the peptide conjugates produced greater proliferation on in vitro stimulation than spleen cells primed with peptide alone. In addition, antibody production as assessed by ELISA was observed after immunization with conjugated peptides but not with peptide alone, indicating B-cell activation. We also found that a high level of IgG2a antibody production correlated with a high level of IFN-γ production. These findings favor the notion that IL-1β plays an important role in immune responses. These observations support the formulation and design of synthetic vaccines against HIV using synthetic HIV peptides conjugated with immunomodulators. Such an approach may provide an effective vaccination against other infectious agents.     

SIV vaccine protection of rhesus monkeys.

Rhesus macaques (M. mulatta), immunized with an inactivated whole SIVmac vaccine and muramyl dipeptide or Freund's incomplete adjuvant, were protected against IV challenge infection with 10 animal infectious doses of the homologous virus. The protection in these animals appeared to be complete, with no breakthrough of latent virus infection over a 10-month period. Vaccine protection in this model was correlated generally with a high level of SIVmac envelope antibody by ELISA and immunoblot, high titers of syncytial inhibiting antibody, and, more specifically, with the presence of antibodies binding to a putative V3 loop synthetic peptide of the SIVmac outer envelope. This model can now be used for further identification of the protective epitopes and protective host immune responses as well as for development of novel and better AIDS vaccines.     

Perspectives of creation of vaccines against tick bite for nonspecific prophylaxis of vector borne diseases

Prophylaxis of infectious diseases transferred by ticks is an important problem of contemporary medicine. One of the perspective approaches to solve this problem is the creation of vaccines against tickbite (anti-tickvaccines). Contemporary methods of the control of infectious diseases transferred by ticks are described in the review. Features of naturally and artificially acquired immunity against ticks are examined. Candidate tick antigens for the construction of vaccines against genus Ixodes tick bite are described. Perspectives of use of anti-tick vaccines against tick vector borne diseases are evaluated.     

DNA vaccines: progress and challenges

In the years following the publication of the initial in vivo demonstration of the ability of plasmid DNA to generate protective immune responses, DNA vaccines have entered into a variety of human clinical trials for vaccines against various infectious diseases and for therapies against cancer, and are in development for therapies against autoimmune diseases and allergy. They also have become a widely used laboratory tool for a variety of applications ranging from proteomics to understanding Ag presentation and cross-priming. Despite their rapid and widespread development and the commonplace usage of the term "DNA vaccines," however, the disappointing potency of the DNA vaccines in humans underscores the challenges encountered in the efforts to translate efficacy in preclinical models into clinical realities. This review will provide a brief background of DNA vaccines including the insights gained about the varied immunological mechanisms that play a role in their ability to generate immune responses.     

Traditional and novel approaches to flavivirus vaccines

Yellow fever, dengue, Japanese encephalitis and tick-borne encephalitis viruses are the medically most important members of the Flavivirus genus composed primarily of arboviruses. In this paper, we review the commercially available traditional flavivirus vaccines against yellow fever, Japanese encephalitis, and tick-borne encephalitis, as well as modern approaches to flavivirus vaccines. Formalin inactivation technology has been employed to produce killed vaccines. Flaviviruses have been attenuated by multiple passages in animal tissues and cell cultures to produce empirical live attenuated vaccines. The use of traditional methods is being pursued to develop vaccines against other flavivirus diseases, such as dengue, and to improve existing vaccines, such as for Japanese encephalitis. With the recent development of infectious clones, rational approaches to attenuated flavivirus vaccines have employed the introduction of specific mutations into wild type viruses and chimerisation between different viruses. Novel methods for delivery of live vaccines, such as inoculation of infectious DNA or RNA, have been described. Other approaches, such as the construction of protein subunit, expression vector-based and naked DNA vaccines, have been proposed to create alternate vaccine candidates.     

Synthetic peptides as cancer vaccines

Effective cancer therapy or prevention has been the dream of physicians and scientists for many years. Although we are still very far from our ultimate goal of cancer prevention, significant milestones have been realized in terms of our knowledge base and understanding of the pathogenesis of cancerous cells and the involvement of the immune system against both self- and virus-associated tumor antigens. Immunotherapeutic strategies are now accepted to being superior in terms of the exquisite specificity that they offer in targeting only tumor cells as opposed to the existent chemotherapy or radiation therapy that is more general and invasive with many associated side effects. There are several immunotherapeutic strategies that are currently under investigation. This review primarily focuses on the significant advances made in the use of synthetic peptides in the development of subunit cancer vaccines. We have attempted to highlight some of the fundamental issues regarding antigen processing and presentation, Major Histocompatibility Complex (MHC) restriction, T-cell help, structural determinants in antibody recognition, and the use of these concepts in the rational design and delivery of peptide vaccines to elicit protective humoral and cell mediated immune responses. The recent use of costimulatory molecules and cytokines to augment immune responses also has been discussed along with the contributions of our laboratory to the field of synthetic peptide vaccine development.     

保护性病毒抗原的筛选策略及其在新型疫苗研发中的应用

随着疫苗研发技术的发展,新型疫苗在传染病的预防中得到了广泛应用。由于新型疫苗安全性良好,因此其在烈性病疫苗的应用中有着得天独厚的优势,然而研制新型疫苗的前提是筛选出保护性抗原。随着各种组学研究的发展,针对真核生物的多种生物信息学方法代表着最前沿的技术手段。相对于真核细胞,病毒具有更为简单的结构,对应着相对简单的研究方法,未来的保护性抗原筛选策略,需要结合生物信息学和传统分子生物学方法的优势。本文分别从宿主和病毒入手,论述了病毒保护性抗原的筛选策略,列举了一系列基于真核细胞开发的可能用于保护性抗原筛选的生物信息学方法,并总结了应用保护性抗原进行新型疫苗设计的案例,以便加深对病毒保护性抗原筛选策略的认知,为新型疫苗的研发提供借鉴。     

Plant‐based oral vaccines against zoonotic and non‐zoonotic diseases

The shared diseases between animals and humans are known as zoonotic diseases and spread infectious diseases among humans. Zoonotic diseases are not only a major burden to livestock industry but also threaten humans accounting for >60% cases of human illness. About 75% of emerging infectious diseases in humans have been reported to originate from zoonotic pathogens. Because antibiotics are frequently used to protect livestock from bacterial diseases, the development of antibiotic‐resistant strains of epidemic and zoonotic pathogens is now a major concern. Live attenuated and killed vaccines are the only option to control these infectious diseases and this approach has been used since 1890. However, major problems with this approach include high cost and injectable vaccines is impractical for >20 billion poultry animals or fish in aquaculture. Plants offer an attractive and affordable platform for vaccines against animal diseases because of their low cost, and they are free of attenuated pathogens and cold chain requirement. Therefore, several plant‐based vaccines against human and animals diseases have been developed recently that undergo clinical and regulatory approval. Plant‐based vaccines serve as ideal booster vaccines that could eliminate multiple boosters of attenuated bacteria or viruses, but requirement of injectable priming with adjuvant is a current limitation. So, new approaches like oral vaccines are needed to overcome this challenge. In this review, we discuss the progress made in plant‐based vaccines against zoonotic or other animal diseases and future challenges in advancing this field.     

Rotavirus Vaccines: New Strategies and Approaches

Rotaviruses cause an infectious disease that is the main cause of severe diarrhea in children all over the world and one of the factors that determine the level of child mortality. Only live attenuated vaccines are currently used against rotavirus infection. These vaccines are efficient, but a range of side effects, including intussusception risk, is characteristic of them. Complications associated with the use of existing vaccines usually occur in the case of oral administration and develop as the attenuated live vaccines start to replicate in the human intestine. Thus, there is a need for development of modern, efficient, and safe preparations for the prevention of rotavirus infection. These preparations should be incapable of reproduction (replication) in the organism after vaccination. Recombinant vaccines represent a new generation of vaccines against rotavirus infection, and the development and testing of such vaccines, including those intended for parenteral administration, has progressed considerably during recent years. The complex antigenic structure of the rotavirus is one of the problems associated with the production of these vaccines. The present review summarizes published data on genetic and antigenic diversity of rotavirus strains and geographic localization of epidemiologically significant virus variants. The role of capsid proteins in the emergence of immune response against the virus and the current state of research on new candidate recombinant vaccines against rotavirus infection are discussed.     

Recombinant viruses as tools to induce protective cellular immunity against infectious diseases.

Infections by intracellular pathogens such as viruses, some bacteria and many parasites, are cleared in most cases after activation of specific T cellular immune responses that recognize foreign antigens and eliminate infected cells. Vaccines against those infectious organisms have been traditionally developed by administration of whole live attenuated or inactivated microorganisms. Nowadays, research is focused on the development of subunit vaccines, containing the most immunogenic antigens from the particular pathogen. However, when purified subunit vaccines are administered using traditional immunization protocols, the levels of cellular immunity induced are mostly low and not capable of eliciting complete protection against diseases caused by intracellular microbes. In this review, we present a promising alternative to those traditional protocols, which is the use of recombinant viruses encoding subunit vaccines as immunization tools. Recombinant viruses have several interesting features that make them extremely efficient at inducing immune responses mediated by T-lymphocytes. This cellular immunity has recently been demonstrated to be of key importance for protection against malaria and AIDS, both of which are major targets of the World Health Organization for vaccine development. Thus, this review will focus in particular on the development of new vaccination protocols against these diseases.     

Predicting antigenic sites on proteins.

The ability to predict antigenic sites on proteins is of major importance for the production of synthetic peptide vaccines and synthetic peptide probes of antibody structure. Many predictive methods, based on various assumptions about the nature of the antigenic response have been proposed and tested. This review will discuss the principles underlying the various approaches to predicting antigenic sites and will attempt to answer the question of how well they work.     

Identification of MHC class II-restricted tumor antigens recognized by CD4+ T cells

CD4+ T cells play a central role in orchestrating host immune responses against cancer as well as autoimmune and infectious diseases. Identification of major histocompatibility complex (MHC) class II-restricted helper T peptides is important for development of effective vaccines. The lack of effective methods to identify such T-cell peptides is a major hurdle in the use of antigen-specific CD4+ T cells in cancer vaccines. Here we describe a genetic targeting expression system for cloning genes encoding for MHC class II-restricted tumor antigens recognized by tumor-reactive CD4+ T cells. Helper T peptides are subsequently identified by using synthetic peptides to test their ability to stimulate CD4+ T cells.     

First peptide vaccine providing protection against viral infection in the target animal: studies of canine parvovirus in dogs.

A synthetic peptide vaccine which protects dogs against challenge with virulent canine parvovirus is described. The amino acid sequence used was discovered in previous studies on the immunogenic properties of previously mapped antigenic sites and represents the amino-terminal region of viral protein VP2. As with marker vaccines, it is possible to discriminate between vaccinated dogs that have not been exposed to the virus and dogs that have been infected with the virus. The protective mechanism can be explained by a humoral response against the peptide aided by T-cell epitopes contained in the carrier protein used for peptide coupling. This is the first example of a synthetic peptide vaccine that induces protection in target animals.