Differential approaches for vaccination from childhood to old age

Primary prevention strategies, such as vaccinations at the age extremes, in neonates and elderly individuals, demonstrate a challenge to health professionals and public health specialists. The aspects of the differentiation and maturation of the adaptive immune system, the functional implications of immunological immaturity or immunosenescence and its impact on vaccine immunogenicity and efficacy will be highlighted in this review. Several approaches have been undertaken to promote Th1 responses in neonates and to enhance immune functions in elderly, such as conjugation to carrier proteins, addition of adjuvants, concomitant vaccination with other vaccines, change in antigen concentrations or dose intervals or use of different administration routes. Also, early protection by maternal vaccination seems to be beneficial in neonates. However, it also appears necessary to think of other end points than antibody concentrations to assess vaccine efficacy in neonates or elderly, as also the cellular immune response may be impaired by the mechanisms of immaturity, underlying health conditions, immunosuppressive treatments or immunosenescence. Thus, lifespan vaccine programs should be implemented to all individuals on a population level not only to improve herd protection and to maintain protective antibody levels and immune memory, but also to cover all age groups, to protect unvaccinated elderly persons and to provide indirect protection for neonates and small infants.

Novel viral vectored vaccines for the prevention of influenza

Influenza represents a substantial global healthcare burden, with annual epidemics resulting in 3-5 million cases of severe illness with a significant associated mortality. In addition, the risk of a virulent and lethal influenza pandemic has generated widespread and warranted concern. Currently licensed influenza vaccines are limited in their ability to induce efficacious and long-lasting herd immunity. In addition, and as evidenced by the H1N1 pandemic in 2009, there can be a significant delay between the emergence of a pandemic influenza and an effective, antibody-inducing vaccine. There is, therefore, a continued need for new, efficacious vaccines conferring cross-clade protection-obviating the need for biannual reformulation of seasonal influenza vaccines. Development of such a vaccine would yield enormous health benefits to society and also greatly reduce the associated global healthcare burden. There are a number of alternative influenza vaccine technologies being assessed both preclinically and clinically. In this review we discuss viral vectored vaccines, either recombinant live-attenuated or replication-deficient viruses, which are current lead candidates for inducing efficacious and long-lasting immunity toward influenza viruses. These alternate influenza vaccines offer real promise to deliver viable alternatives to currently deployed vaccines and more importantly may confer long-lasting and universal protection against influenza viral infection.

Development of a virosomal malaria vaccine candidate: from synthetic peptide design to clinical concept validation

An ideal malaria vaccine would prevent disease and reduce transmission by targeting several developmental stages of human malaria parasites. To be cost-effective, a modular antigen delivery technology is required for the development of such a multivalent subunit vaccine. In this review, we summarize and discuss a strategy to develop synthetic peptidomimetics of key malaria target antigens for inclusion in a multivalent malaria subunit vaccine based on immunopotentiating reconstituted influenza virosomes. Clinical testing of a bivalent virosomal formulation incorporating two structurally optimized peptidomimetics has demonstrated safety, immunogenicity and pilot efficacy. While this clinical validation supports the concept of using peptide-loaded virosomes for vaccination in humans, it is assumed that additional antigens will have to be added to the bivalent formulation to generate a highly effective malaria vaccine.

Recent progress in vaccines against fungal diseases

Diseases caused by fungi are increasingly impacting the health of the human population and now account for a large fraction of infectious disease complications in individuals with impaired immunity or breached tissue defenses. Antifungal therapy is often of limited effectiveness in these patients, resulting into treatment failures, chronic infections and unacceptable rates of mortality, morbidity and their associated costs. Consequently there is a real medical need for new treatments and preventive measures to combat fungal diseases and, toward this goal, safe and efficacious vaccines would constitute major progress. After decades of complacency and neglect of this critically important field of research, remarkable progress has been made in recent years. A number of highly immunogenic and protective vaccine formulations in preclinical setting have been developed, and at least two have undergone Phase 1 clinical trials as preventive and/or therapeutic tools against candidiasis.

A virosomal vaccine against candidal vaginitis: immunogenicity, efficacy and safety profile in animal models

A novel vaccine (PEV7) consisting of a truncated, recombinant aspartyl proteinase-2 of Candida albicans incorporated into influenza virosomes was studied. This vaccine candidate generated a potent serum antibody response in mouse and rat following intramuscular immunization. Anti-Sap2 IgG and IgA were also detected in the vaginal fluid of rats following intravaginal or intramuscular plus intravaginal administration. In a rat model of candidal vaginitis, PEV7 induced significant, long-lasting, likely antibody-mediated, protection following intravaginal route of immunization. PEV7 was also found to be safe in a repeated-dose toxicological study in rats. Overall, these data provide a sound basis to envisage the clinical development of this new candidate vaccine against candidal vaginitis.

Adjuvants for human vaccines

Rational selection of individual adjuvants can often be made on the basis of innate molecular interactions of the foreign molecules with pattern recognition receptors such as Toll-like receptors. For example, monophosphoryl lipid A, a family of endotoxic TLR4 agonist molecules from bacteria, has recently been formulated with liposomes, oil emulsions, or aluminum salts for several vaccines. Combinations of antigens and adjuvants with particulate lipid or oil components may reveal unique properties of immune potency or efficacy, but these can sometimes be exhibited differently in rodents when compared to nonhuman primates or humans. New adjuvants, formulations, microinjection devices, and skin delivery techniques for transcutaneous immunization demonstrate that adjuvant systems can include combinations of strategies and delivery mechanisms for uniquely formulated antigens and adjuvants.

Chlamydia vaccines: recent developments and the role of adjuvants in future formulations

Bacteria of the genus Chlamydia cause a plethora of ocular, genital and respiratory diseases that continue to pose a considerable public health challenge worldwide. The major diseases are conjunctivitis and blinding trachoma, non-gonococcal urethritis, cervicitis, pelvic inflammatory disease, ectopic pregnancy, tubal factor infertility and interstitial pneumonia. The rampart asymptomatic infections prevent timely and effective antibiotic treatments, and quite often clinical presentation of sequelae is the first evidence of an infection. Besides, significant broad coverage in population screening and treatment is economically and logistically impractical, and mass education for public awareness has been ineffective. The current medical opinion is that an efficacious prophylactic vaccine is the best approach to protect humans from chlamydial infections. Unfortunately, a human vaccine has yet to be realized despite successful veterinary vaccines. Fortunately, recent advances in chlamydial immunobiology, cell biology, molecular pathogenesis, genomics, antigen discovery and animal models of infections are hastening progress toward an efficacious vaccine. Thus, it is established that Chlamydia immunity is mediated by T cells and a complementary antibody response, and several potential vaccine candidates have been identified. However, further advances are needed in effective vaccine delivery systems and safe potent adjuvants to boost and sustain immune responses for long-lasting protective immunity. This article focuses on the current status of human chlamydial vaccine research, specifically how application of new delivery systems and human compatible adjuvants could lead to a timely achievement of efficacious Chlamydia vaccines. The ranking of the candidate vaccine antigens for human vaccine development will await the availability of results from studies in which the antigens are tested by comparable experimental standards, such as antigen-adjuvant combination, route of delivery and possible toxicity.

Towards tailored vaccine delivery: needs, challenges and perspectives

The ideal vaccine is a simple and stable formulation which can be conveniently administered and provides life-long immunity against a given pathogen. The development of such a vaccine, which should trigger broad and strong B-cell and T-cell responses against antigens of the pathogen in question, is highly dependent on tailored vaccine delivery approaches. This review addresses vaccine delivery in its broadest scope. We discuss the needs and challenges in the area of vaccine delivery, including restrictions posed by specific target populations, potentials of dedicated stable formulations and devices, and the use of adjuvants. Moreover, we address the current status and perspectives of vaccine delivery via several routes of administration, including non- or minimally invasive routes. Finally we suggest possible directions for future vaccine delivery research and development.

Targeting nanoparticles to dendritic cells for immunotherapy

Dendritic cells (DCs) are key players in the initiation of adaptive immune responses and are currently exploited in immunotherapy for treatment of cancer and infectious diseases. Development of targeted nanodelivery systems carrying vaccine components, including antigens and adjuvants, to DCs in vivo represents a promising strategy to enhance immune responses. Delivering particulate vaccines specifically to DCs and preventing nonspecific uptake by other endocytotic cells are challenging. Size represents a critical parameter determining whether particulate vaccines can penetrate lymph nodes and reach resident DCs. Specific delivery is further enhanced by actively targeting DC-specific receptors. This chapter discusses the rationale for the use of particle-based vaccines and provides an overview of antigen-delivery vehicles currently under investigation. In addition, we discuss how vaccine delivery systems may be developed, focusing on liposomes, PLGA polymers, and gold nanoparticles, to obtain safe and efficacious vaccines.

New adjuvants in evolving vaccine strategies

Adjuvants are becoming the key players of vaccine formulations to enhance the immunogenicity of subunit (peptides, proteins, virus-like particles (VLPs)) and DNA vaccines, as well as to reach the current new goals of preventing and/or treating chronic infectious diseases and cancers. Induction of humoral response, in particular neutralizing antibodies able to inhibit the binding of pathogens to their cellular receptors, remains a major goal of vaccines targeted to prevent acute lytic infections; induction/modulation of cellular immunity is, however, critical to fight latently/chronically infected cells as well as cancer cells. The new adjuvants, included in vaccine preparations, are currently able to modify the presentation of epitopes to the immune system with a specific T(H)1 versus T(H)2 polarization efficacy. A paradigm of the relevance of these new adjuvants is the immunological result obtained with the inclusion of monophosphoryl lipid A in the formulation of L1-based human papillomavirus (HPV)-naked VLPs. In the May issue of this journal, Garcon and colleagues describe the highly enhanced humoral and memory B cellular immunity of the AS04-adjuvanted HPV vaccine, which results in a long-lasting and broad spectrum immunity.