Overview of vaccines

This article lists the vaccines current available for the control of both viral and bacterial infections. They may be attenuated live or inactivated whole microorganisms, or subunit preparations. Many more are in the pipeline and increasing attention is being given to establishing their safety before registration. Following the earlier eradication of smallpox, good progress is now being made toward the global eradication of poliomyelitis and a new program to eliminate measles from the Americas has begun. A variety of new approaches to vaccine development is now available. The hepatitis B virus surface antigen, made by DNA-transfected yeast or mammalian cells, is the basis of the first genetically engineered vaccine. Early in the 21st century, new vaccines based on oligopeptides, recombinant live viral or bacterial vectors (often existing live vaccines), or recombinant DNA plasmids are likely to be registered for human use. The efficacy of vaccines depends on the immune responses generated, and the recent substantial increase in our understanding of the mammalian immune system now offers great opportunities for manipulation to best obtain desired responses. These include mixing vaccine formulations to maximize immune responses, and combining vaccines to simplify their administration. Despite these advances, some persisting infections, such as those caused by HIV, plasmodia, and mycobacteria, still pose a great challenge to vaccine developers.     

Subdominant Antigens in Bacterial Vaccines: AM779 Is Subdominant in the Anaplasma marginale Outer Membrane Vaccine but Does Not Associate with Protective Immunity

Identification of specific antigens responsible for the ability of complex immunogens to induce protection is a major goal in development of bacterial vaccines. Much of the investigation has focused on highly abundant and highly immunodominant outer membrane proteins. Recently however, genomic and proteomic approaches have facilitated identification of minor components of the bacterial outer membrane that have previously been missed or ignored in immunological analyses. Immunization with Anaplasma marginale outer membranes or a cross-linked surface complex induces protection against bacteremia, however the components responsible for protection within these complex immunogens are unknown. Using outer membrane protein AM779 as a model, we demonstrated that this highly conserved but minor component of the A. marginale surface was immunologically sub-dominant in the context of the outer membrane or surface complex vaccines. Immunologic sub-dominance could be overcome by targeted vaccination with AM779 for T lymphocyte responses but not for antibody responses, suggesting that both abundance and intrinsic immunogenicity determine relative dominance. Importantly, immunization with AM779 supports that once priming is achieved by specific targeting, recall upon infectious challenge is achieved. While immunization with AM779 alone was not sufficient to induce protection, the ability of targeted immunization to prime the immune response to highly conserved but low abundance proteins supports continued investigation into the role of sub-dominant antigens, individually and collectively, in vaccine development for A. marginale and related bacterial pathogens.     

广谱流感疫苗的研究进展

流行性感冒(简称流感)的频频暴发严重危害人类健康和公共卫生,已引起全球范围内的高度关注。预防流感最有效和经济的措施是接种疫苗,但流感病毒的持续变异可逃逸人群已有的免疫应答,目前使用的季节性流感疫苗仅对亚型内抗原匹配较好的毒株产生免疫保护作用,难以有效应对因抗原漂移或抗原转换而产生的无法预料的流感大流行。因此,研发对流感病毒不同亚型均具有交叉免疫保护作用的广谱流感疫苗具有重要意义。近年来,流感病毒广谱中和抗体的发现、对流感病毒抗原保守区域及细胞免疫机制的深入研究、疫苗免疫策略的优化等都为广谱流感疫苗的研发提供了新思路。本文简述了近几年基于血凝素、基质蛋白、核蛋白等多种流感靶抗原的广谱流感疫苗的研究进展。     

The challenges of eliciting neutralizing antibodies to HIV-1 and to influenza virus

The ability to elicit broadly neutralizing antibody responses against HIV-1 is a crucial goal for a prophylactic HIV-1 vaccine. Here, we discuss the difficulties of achieving broad HIV-1 neutralization in the context of both the effective annual human influenza virus vaccine and the need to develop a pandemic influenza vaccine. Immunogen-design strategies are underway to target functionally conserved regions of the HIV-1 envelope glycoproteins, and similar strategies might be applicable to pandemic influenza virus vaccine development. Efforts to develop broadly neutralizing vaccines against either HIV-1 or influenza virus might establish a paradigm for future vaccines against highly variable pathogens.     

HIV-1壳体蛋白的结构及其病毒样颗粒疫苗

人类免疫缺陷病毒(HIV)的壳体蛋白(CA)在HIV病毒的组装和成熟过程中起着至关重要的作用。近年来,壳体蛋白的体外表达及其疫苗的研制成了HIV各项研究的焦点。由于壳体蛋白具有较好的的保守性,用其制得的疫苗也会提供比包膜蛋白更为广泛的免疫保护力。另外若将CA在体外表达成一个颗粒状结构,会增强其免疫原性,可以使疫苗发挥出更大的效力。     

活菌疫苗载体的研究与应用

目前在疫苗研究中,要求新型疫苗不仅能够激发高效持久的免疫应答,而且应易于接种、生产费用低。减毒或无毒的活微生物作为疫苗载体能够激起持久的系统和黏膜免疫反应,批量制备成本较低,且具有良好的安全性,近年来已成为疫苗研究领域的热点。本文综述了几种活菌疫苗载体,包括沙门氏菌、卡介苗、耶尔森菌等的研究状况及其在疫苗载体方面的应用。     

Current concepts in cancer vaccine strategies

Cancer vaccines are entering a new phase of popularity, in part because of the recognition of when a therapeutic vaccine is most effective and the identification of appropriate target antigens. New technologies, most notably gene transfection into dendritic cell and DNA vaccination approaches, have spurred further clinical evaluations. While many researchers consider humoral responses as not being viable for large tumors, these responses may play a role in regulating micrometastases (i.e., adjuvant setting). The recent approval of antibodies as therapeutics for cancer treatment has lent to the viability of this therapy concept. The success of carbohydrate-conjugate vaccines in bacterial systems has also renewed interest in developing such vaccines for cancer immunotherapy. Carbohydrates can be further converted into peptide/protein mimetics with several of these mimetics in clinical trials. These mimetic forms can be manipulated into DNA vaccine types that may be combined into DNA cassettes that contain CTL-associated epitopes to further define a novel strategy for future vaccine development.     

Anti-CD25 antibody enhancement of vaccine-induced immunogenicity: increased durable cellular immunity with reduced immunodominance

An efficacious vaccine strategy must be capable of inducing strong responses of an appropriate phenotype that are long lasting and sufficiently broad to prevent pathogen escape mechanisms. In the present study, we use anti-CD25 mAb to augment vaccine-induced immunity in mice. We demonstrate that coformulation of Ab and poxviral- or adenoviral-vectored vaccines induces significantly increased T cell responses to a malaria Ag; prior anti-CD25 Ab administration was not required for this effect. Furthermore, this vaccination approach subverts immunodominant epitope hierarchies by enhancing responses to subdominant epitopes induced by recombinant modified vaccinia virus Ankara immunization. Administration of anti-CD25 with a vaccine also induces more durable immunity compared with vaccine alone; significantly higher T cell responses were observed 100 days after the primary immunization. Enhanced immunogenicity is observed for multiple vaccine types with enhanced CD4+ and CD8+ T cell responses induced by bacillus Calmette-Guérin and a recombinant subunit protein vaccine to hepatitis B virus and with multiple Ags of tumor, viral, bacterial, and parasitic origin. Vaccine strategies incorporating anti-CD25 lead to improved protection against pre-erythrocytic malaria challenge. These data underpin new strategies for the design and development of more efficacious vaccines in clinical settings.     

DNA vaccines

Within the last decade bacterial plasmids encoding foreign antigens have revolutionized vaccine design. Although no DNA vaccine has yet been approved for routine human or veterinary use, the potential of this vaccine modality has been demonstrated in experimental animal models. Plasmid DNA vaccination has shown efficacy against viral, bacterial and parasitic infections, modulated the effects of autoimmune and allergic diseases and induced control over cancer progression. With a better understanding of the basic immune mechanisms that govern induction of protective or curative immune responses, plasmid DNA vaccines and their mode of delivery are continuously being optimized. Because of the simplicity and versatility of these vaccines, various routes and modes of delivery are possible to engage the desired immune responses. These may be T or B effector cell responses able to eliminate infectious agents or transformed cells. DNA vaccines may also induce an immunoregulatory/modulatory or immunosuppressive (tolerizing) response that interferes with the differentiation, expansion or effector functions of B and T cells. In this sense a DNA vaccine may be thought of as a 'negative' vaccine. Pre-clinical and initial small-scale clinical trials have shown DNA vaccines in either of these modes to be safe and well tolerated. Although DNA vaccines induce significant immune responses in small animal trials their efficacy in humans has so far been less promising thus necessitating additional optimizations of this novel vaccine approach.     

Measles: immune suppression and immune responses

Measles is a highly contagious viral disease that remains the leading vaccine-preventable cause of child mortality worldwide. Deaths from measles are due largely to an increased susceptibility to secondary bacterial and viral infections, attributed to a prolonged state of immune suppression. Several abnormalities of the immune system have been described, including changes in lymphocyte number and function, shifts in cytokine responses, immunomodulatory effects of interleukin-10, down regulation of interleukin-12, impaired antigen presentation, and altered interferon alpha/beta signaling pathways. Although the current vaccine is very effective, knowledge of the molecular basis of the immune responses to measles virus could contribute to the development of a safer, more immunogenic measles vaccine. However, the safety of new measles vaccines must be carefully investigated, as two measles vaccines have resulted in unintended immunologic consequences: atypical measles following administration of the formalin-inactivated measles vaccine and increased mortality in girls following administration of high-titer measles vaccines.     

Synthetic Long Peptide Influenza Vaccine Containing Conserved T and B Cell Epitopes Reduces Viral Load in Lungs of Mice and Ferrets

Currently licensed influenza vaccines mainly induce antibodies against highly variable epitopes. Due to antigenic drift, protection is subtype or strain-specific and regular vaccine updates are required. In case of antigenic shifts, which have caused several pandemics in the past, completely new vaccines need to be developed. We set out to develop a vaccine that provides protection against a broad range of influenza viruses. Therefore, highly conserved parts of the influenza A virus (IAV) were selected of which we constructed antibody and T cell inducing peptide-based vaccines. The B epitope vaccine consists of the highly conserved HA2 fusion peptide and M2e peptide coupled to a CD4 helper epitope. The T epitope vaccine comprises 25 overlapping synthetic long peptides of 26-34 amino acids, thereby avoiding restriction for a certain MHC haplotype. These peptides are derived from nucleoprotein (NP), polymerase basic protein 1 (PB1) and matrix protein 1 (M1). C57BL/6 mice, BALB/c mice, and ferrets were vaccinated with the B epitopes, 25 SLP or a combination of both. Vaccine-specific antibodies were detected in sera of mice and ferrets and vaccine-specific cellular responses were measured in mice. Following challenge, both mice and ferrets showed a reduction of virus titers in the lungs in response to vaccination. Summarizing, a peptide-based vaccine directed against conserved parts of influenza virus containing B and T cell epitopes shows promising results for further development. Such a vaccine may reduce disease burden and virus transmission during pandemic outbreaks.     

Live bacterial vaccines – a review and identification of potential hazards

The use of live bacteria to induce an immune response to itself or to a carried vaccine component is an attractive vaccine strategy. Advantages of live bacterial vaccines include their mimicry of a natural infection, intrinsic adjuvant properties and their possibility to be administered orally. Derivatives of pathogenic and non-pathogenic food related bacteria are currently being evaluated as live vaccines. However, pathogenic bacteria demands for attenuation to weaken its virulence. The use of bacteria as vaccine delivery vehicles implies construction of recombinant strains that contain the gene cassette encoding the antigen. With the increased knowledge of mucosal immunity and the availability of genetic tools for heterologous gene expression the concept of live vaccine vehicles gains renewed interest. However, administration of live bacterial vaccines poses some risks. In addition, vaccination using recombinant bacteria results in the release of live recombinant organisms into nature. This places these vaccines in the debate on application of genetically modified organisms. In this review we give an overview of live bacterial vaccines on the market and describe the development of new live vaccines with a focus on attenuated bacteria and food-related lactic acid bacteria. Furthermore, we outline the safety concerns and identify the hazards associated with live bacterial vaccines and try to give some suggestions of what to consider during their development.     

Attenuated Salmonella enterica serovar Typhi and Shigella flexneri 2a strains mucosally deliver DNA vaccines encoding measles virus hemagglutinin,inducing specific immune responses and protection in cotton rats

Measles remains a leading cause of child mortality in developing countries. Residual maternal measles antibodies and immunologic immaturity dampen immunogenicity of the current vaccine in young infants. Because cotton rat respiratory tract is susceptible to measles virus (MV) replication after intranasal (i.n.) challenge, this model can be used to assess the efficacy of MV vaccines. Pursuing a new measles vaccine strategy that might be effective in young infants, we used attenuated Salmonella enterica serovar Typhi CVD 908-htrA and Shigella flexneri 2a CVD 1208 vaccines to deliver mucosally to cotton rats eukaryotic expression plasmid pGA3-mH and Sindbis virus-based DNA replicon pMSIN-H encoding MV hemagglutinin (H). The initial i.n. dose-response with bacterial vectors alone identified a well-tolerated dosage (1 x 10(9) to 7 x 10(9) CFU) and a volume (20 micro l) that elicited strong antivector immune responses. Animals immunized i.n. on days 0, 28, and 76 with bacterial vectors carrying DNA plasmids encoding MV H or immunized parenterally with these naked DNA vaccine plasmids developed MV plaque reduction neutralizing antibodies and proliferative responses against MV antigens. In a subsequent experiment of identical design, cotton rats were challenged with wild-type MV 1 month after the third dose of vaccine or placebo. MV titers were significantly reduced in lung tissue of animals immunized with MV DNA vaccines delivered either via bacterial live vectors or parenterally. Since attenuated serovar Typhi and S. flexneri can deliver measles DNA vaccines mucosally in cotton rats, inducing measles immune responses (including neutralizing antibodies) and protection, boosting strategies can now be evaluated in animals primed with MV DNA vaccines.     

MHC Class I-Presented T Cell Epitopes Identified by Immunoproteomics Analysis Are Targets for a Cross Reactive Influenza-Specific T Cell Response

Influenza virus infection and the resulting complications are a significant global public health problem. Improving humoral immunity to influenza is the target of current conventional influenza vaccines, however, these are generally not cross-protective. On the contrary, cell-mediated immunity generated by primary influenza infection provides substantial protection against serologically distinct viruses due to recognition of cross-reactive T cell epitopes, often from internal viral proteins conserved between viral subtypes. Efforts are underway to develop a universal flu vaccine that would stimulate both the humoral and cellular immune responses leading to long-lived memory. Such a universal vaccine should target conserved influenza virus antibody and T cell epitopes that do not vary from strain to strain. In the last decade, immunoproteomics, or the direct identification of HLA class I presented epitopes, has emerged as an alternative to the motif prediction method for the identification of T cell epitopes. In this study, we used this method to uncover several cross-specific MHC class I specific T cell epitopes naturally presented by influenza A-infected cells. These conserved T cell epitopes, when combined with a cross-reactive antibody epitope from the ectodomain of influenza M2, generate cross-strain specific cell mediated and humoral immunity. Overall, we have demonstrated that conserved epitope-specific CTLs could recognize multiple influenza strain infected target cells and, when combined with a universal antibody epitope, could generate virus specific humoral and T cell responses, a step toward a universal vaccine concept. These epitopes also have potential as new tools to characterize T cell immunity in influenza infection, and may serve as part of a universal vaccine candidate complementary to current vaccines.     

Flu Universal Vaccines: New Tricks on an Old Virus

Conventional influenza vaccines are based on predicting the circulating viruses year by year, conferring limited effectiveness since the antigenicity of vaccine strains does not always match the circulating viruses. This necessitates development of universal influenza vaccines that provide broader and lasting protection against pan-influenza viruses. The discovery of the highly conserved immunogens(epitopes) of influenza viruses provides attractive targets for universal vaccine design. Here we review the current understanding with broadly protective immunogens(epitopes) and discuss several important considerations to achieve the goal of universal influenza vaccines.     

Utilizing bacterial flagellins against infectious diseases and cancers

The flagellum is the organelle providing motility to bacterial cells and its activity is coupled to the cellular chemotaxis machinery. The flagellar filament is the largest portion of the flagellum, which consists of repeating subunits of the protein flagellin. Receptors of the innate immune system including Toll like receptor 5, ICE protease activating factor, and neuronal apoptosis inhibitory protein 5 signal in response to bacterial flagellins. In addition to inducing innate immune responses, bacterial flagellins mediate the development of adaptive immune responses to both flagellins and coadministered antigens. Therefore, these proteins have intensively been investigated for the vaccine development and the immunotherapy. This review describes the utilization of bacterial flagellins for the construction of vaccines against infectious diseases and cancer immunotherapy. Furthermore, the key factors affecting the performance of these systems are highlighted.     

Dendritic cell‐targeting DNA‐based nasal adjuvants for protective mucosal immunity to Streptococcus pneumoniae

To develop safe vaccines for inducing mucosal immunity to major pulmonary bacterial infections, appropriate vaccine antigens (Ags), delivery systems and nontoxic molecular adjuvants must be considered. Such vaccine constructs can induce Ag‐specific immune responses that protect against mucosal infections. In particular, it has been shown that simply mixing the adjuvant with the bacterial Ag is a relatively easy means of constructing adjuvant‐based mucosal vaccine preparations; the resulting vaccines can elicit protective immunity. DNA‐based nasal adjuvants targeting mucosal DCs have been studied in order to induce Ag‐specific mucosal and systemic immune responses that provide essential protection against microbial pathogens that invade mucosal surfaces. In this review, initially a plasmid encoding the cDNA of Flt3 ligand (pFL), a molecule that is a growth factor for DCs, as an effective adjuvant for mucosal immunity to pneumococcal infections, is introduced. Next, the potential of adding unmethylated CpG oligodeoxynucleotide and pFL together with a pneumococcal Ag to induce protection from pneumococcal infections is discussed. Pneumococcal surface protein A has been used as vaccine for restoring mucosal immunity in older persons. Further, our nasal pFL adjuvant system with phosphorylcholine‐keyhole limpet hemocyanin (PC‐KLH) has also been used in pneumococcal vaccine development to induce complete protection from nasal carriage by Streptococcus pneumoniae . Finally, the possibility that anti‐PC antibodies induced by nasal delivery of pFL plus PC‐KLH may play a protective role in prevention of atherogenesis and thus block subsequent development of cardiovascular disease is discussed.

     

Strategies for cancer therapy using carcinoembryonic antigen vaccines

Advances in molecular biology and immunology have renewed interest in the development of vaccines for the treatment or prevention of cancer. Research over the past 10 years has focused on the identification of suitable tumour antigens to use as targets for a variety of vaccine strategies. Carcinoembryonic antigen (CEA) was one of the first tumour antigens described, and is commonly expressed by a wide range of adenocarcinomas. Recent studies have identified several human-leukocyte-antigen-restricted epitopes (short peptides) within the CEA protein that can be recognised by human T lymphocytes (T cells). Although CEA-expressing tumour cells are generally weakly recognised by the immune system, several new strategies have been used to enhance immune responses against CEA. This includes using antibodies directed against CEA; inserting the CEA gene into recombinant viruses and bacteria as viral and bacterial vaccines; pulsing the CEA protein, peptides, DNA or RNA onto dendritic cells (specialised antigen-presenting cells); and combining CEA vaccines with cytokines or co-stimulatory molecules to increase vaccine effectiveness. Other factors that might be important in establishing systemic immunity against CEA are the dose, route, timing, and choice of vector and adjuvants for vaccine administration. Further research in understanding the fundamental processes involved in tumour-cell recognition by the immune system, better animal models, and improved clinical trial designs will help to define the full potential of CEA as a target for cancer vaccine development.     

Protection from bacterial infection by a single vaccination with replication-deficient mutant herpes simplex virus type 1

Adaptive immune responses in which CD8(+) T cells recognize pathogen-derived peptides in the context of major histocompatibility complex class I molecules play a major role in the host defense against infection with intracellular pathogens. Cells infected with intracellular bacteria such as Listeria monocytogenes, Salmonella enterica serovar Typhimurium, or Mycobacterium tuberculosis are directly lysed by cytotoxic CD8(+) T cells. For this reason, current vaccines for intracellular pathogens, such as subunit vaccines or viable bacterial vaccines, aim to generate robust cytotoxic T-cell responses. In order to investigate the capacity of a herpes simplex virus type 1 (HSV-1) vector to induce strong cytotoxic effector cell responses and protection from infection with intracellular pathogens, we developed a replication-deficient, recombinant HSV-1 (rHSV-1) vaccine. We demonstrate in side-by-side comparison with DNA vaccination that rHSV-1 vaccination induces very strong CD8(+) effector T-cell responses. While both vaccines provided protection from infection with L. monocytogenes at low, but lethal doses, only rHSV-1 vaccines could protect from higher infectious doses; HSV-1 induced potent memory cytotoxic T lymphocytes that, upon challenge by pathogens, efficiently protected the animals. Despite the stimulation of relatively low humoral and CD4-T-cell responses, rHSV-1 vectors are strong candidates for future vaccine strategies that confer efficient protection from subsequent infection with intracellular bacteria.