Recombinant poxviruses as mucosal vaccine vectors

Progress towards an AIDS mucosal vaccine: An overview

The mucosal immune system acts as a first line of defense against infection caused by luminal pathogens. Because HIV is transmitted primarily via mucosal-associated tissues, particularly with sexual transmission, understanding antiviral immunity present at these sites is important. HIV infection results in depletion of gut-associated lymphoid tissue (GALT) and in this sense can be considered to be a disease of the mucosal immune system. A stumbling block for efforts to develop a vaccine against this disease has been the escape of vaccine-induced neutralizing antibodies and cytotoxic T lymphocytes (CTLs) at mucosal compartments and the resulting viral spread. To avoid these problems, the ideal mucosal vaccine would induce HIV-specific secretory IgA (S-IgA) and mucosal CD8(+) CTL as a first line of defense at a very early stage of HIV infection, before the virus can seed into the secondary lymphoid organs in mucosal and systemic tissues. In this review, we provide an overview of mucosal vaccine concepts and vaccination strategies that have been proposed for the development of an HIV mucosal vaccine, including live recombinant vaccines, peptide-based vaccines, virus-like particles (VLP), subunit vaccines and DNA vaccines.

Recent advances in delivery systems for anti-HIV1 therapy

In the last years, different non-biological and biological carrier systems have been developed for anti-HIV1 therapy. Liposomes are excellent potential anti-HIV1 carriers that have been tested with drugs, antisense oligonucleotides, ribozymes and therapeutic genes. Nanoparticles and low-density lipoproteins (LDLs) are cell-specific transporters of drugs against macrophage-specific infections such as HIV1. Through a process of protein transduction, cell-permeable peptides of natural origin or designed artificially allow the delivery of drugs and genetic material inside the cell. Erythrocyte ghosts and bacterial ghosts are a promising delivery system for therapeutic peptides and HIV vaccines. Of interest are the advances made in the field of HIV gene therapy by the use of autologous haematopoietic stem cells and viral vectors for HIV vaccines. Although important milestones have been reached in the development of carrier systems for the treatment of HIV, especially in the field of gene therapy, further clinical trials are required so that the efficiency and safety of these new systems can be guaranteed in HIV patients.

T-Cell epitope discovery for variola and vaccinia viruses

Variola major, the causative agent of smallpox, afflicted mankind throughout history until the worldwide World Health Organisation WHO vaccination campaign successfully eradicated the disease. Unfortunately, recent concerns about bioterrorism have renewed scientific interest in this virus. One essential component of our biodefense and preparedness efforts is an understanding of poxvirus immunity. To this end a number of laboratories have sought to discover T- and B-Cell epitopes from select agents such as variola virus. This review focuses on the efforts to identify CD8(+) T-Cell epitopes from poxviruses as a means to develop new vaccines and therapeutics. A wide variety of techniques have been employed by several research groups to provide complementary information regarding cellular immune responses to poxviruses. In the last several years well over 100 T-Cell epitopes have been identified and the work rapidly continues. The information gleaned from these studies will not only give us a greater understanding of immunity to variola virus and other viruses, but also provide a foundation for next generation vaccines and additional tools with which to study host-pathogen interactions.

Vaccination with recombinant modified vaccinia virus Ankara expressing bovine respiratory syncytial virus (bRSV) proteins protects calves against RSV challenge

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and calves. Bovine RSV (bRSV) is a natural pathogen for cattle, and bRSV infection in calves shares many features with the human infection. Thus, bRSV infection in cattle provides the ideal setting to evaluate the safety and efficacy of novel RSV vaccine strategies. Here, we have evaluated the efficacy and safety of modified vaccinia virus Ankara (rMVA)-based vaccine candidates, expressing the bovine RSV-F protein, either or not in combination with the G protein, in colostrums-deprived SPF calves born by caesarean section. Vaccination induced bRSV-specific IgG and CD8 T cell responses. Importantly, no IgE responses were detected. After bRSV challenge, rMVA vaccinated calves experienced less severe symptoms of lower respiratory tract disease compared to the mock-immunized control group. Immunized animals showed reduced pulmonary virus loads, and no eosinophilic infiltration or enhanced respiratory distress. In conclusion, candidate rMVA/bRSV vaccines induced protective and safe immune responses in calves.

Generation and evaluation of a recombinant modified vaccinia virus Ankara vaccine for rabies

Modified vaccinia virus Ankara (MVA) has become a vaccine vector of choice for recombinant vaccine development. A MVA-based rabies vaccine would be advantageous for use as a vaccine for dogs (and wildlife), particularly if it proves innocuous and efficacious by the oral route. Here, the generation and immunological testing of a recombinant MVA expressing a rabies virus glycoprotein gene is described. In a murine model, higher dosages of recombinant MVA were needed to induce equivocal immune responses as with Vaccinia Copenhagen or Vaccinia Western Reserve recombinants, when administered by a parenteral route. The MVA recombinant was not immunogenic or efficacious when administered per os in naïve mice. The ability of the recombinant MVA to induce anamnestic responses in dogs and raccoons was also investigated. Recombinant MVA boosted humoral immune responses in these animals when administered peripherally, but not when administered orally.

Vaccines for viral and parasitic diseases produced with baculovirus vectors

The baculovirus-insect cell expression system is an approved system for the production of viral antigens with vaccine potential for humans and animals and has been used for production of subunit vaccines against parasitic diseases as well. Many candidate subunit vaccines have been expressed in this system and immunization commonly led to protective immunity against pathogen challenge. The first vaccines produced in insect cells for animal use are now on the market. This chapter deals with the tailoring of the baculovirus-insect cell expression system for vaccine production in terms of expression levels, integrity and immunogenicity of recombinant proteins, and baculovirus genome stability. Various expression strategies are discussed including chimeric, virus-like particles, baculovirus display of foreign antigens on budded virions or in occlusion bodies, and specialized baculovirus vectors with mammalian promoters that express the antigen in the immunized individual. A historical overview shows the wide variety of viral (glyco)proteins that have successfully been expressed in this system for vaccine purposes. The potential of this expression system for antiparasite vaccines is illustrated. The combination of subunit vaccines and marker tests, both based on antigens expressed in insect cells, provides a powerful tool to combat disease and to monitor infectious agents.