BrazilianRecombinant Journal viruses of Medical as vaccines and Biological Research (2005) 38: 509-522 509 ISSN 0100-879X Review Recombinant viruses as vaccines against viral diseases A.P.D. Souza1, 1Departamento de Microbiologia e Parasitologia, L. Haut1, Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil A. Reyes-Sandoval2 2Wellcome Trust Centre for Human Genetics, University of Oxford, and A.R. Pinto1 Roosevelt Drive, Oxford, UK Abstract Correspondence Vaccine approaches to infectious diseases are widely applied and Key words A.R. Pinto appreciated. Amongst them, vectors based on recombinant viruses • Vaccine Departamento de Microbiologia e have shown great promise and play an important role in the develop- • Immunity Parasitologia, UFSC ment of new vaccines. Many viruses have been investigated for their • Recombinant viruses 88040-900 Florianópolis, SC ability to express proteins from foreign pathogens and induce specific • Viral vectors Brasil • Infectious disease Fax: +55-48-331-9258 immunological responses against these antigens in vivo. Generally, E-mail: [email protected] gene-based vaccines can stimulate potent humoral and cellular im- mune responses and viral vectors might be an effective strategy for A.R. Pinto is supported by Fundação both the delivery of antigen-encoding genes and the facilitation and de Ciência e Tecnologia do Estado enhancement of antigen presentation. In order to be utilized as a de Santa Catarina (FUNCITEC) and vaccine carrier, the ideal viral vector should be safe and enable Programa Nacional de DST/AIDS, efficient presentation of required pathogen-specific antigens to the Ministério da Saúde, Brasil. immune system. It should also exhibit low intrinsic immunogenicity to allow for its re-administration in order to boost relevant specific immune responses. Furthermore, the vector system must meet criteria Received August 30, 2004 that enable its production on a large-scale basis. Several viral vaccine Accepted February 21, 2005 vectors have thus emerged to date, all of them having relative advan- tages and limits depending on the proposed application, and thus far none of them have proven to be ideal vaccine carriers. In this review we describe the potential, as well as some of the foreseeable obstacles associated with viral vaccine vectors and their use in preventive medicine. Introduction smallpox infections. Since then, smallpox has been eradicated worldwide and other Vaccination has been one of the most diseases such as poliomyelitis have virtually important interventions designed to prevent disappeared in countries of the Western Hemi- disease to be employed on a worldwide ba- sphere and it is expected that some of these sis, second only to the improvement of sani- diseases will become globally eradicated in tation services and the provision of clean the near future. Also, vaccination has effec- drinking water. The concept of vaccinology tively limited the spread of many childhood originated in the 18th century when the En- and adult diseases, including measles, glish physician Edward Jenner used cowpox mumps, rubella, and hepatitis B. However, virus inoculations in an attempt to combat efforts to develop vaccines for remaining or Braz J Med Biol Res 38(4) 2005 510 A.P.D. Souza et al. emerging infectious agents, like malaria, components of the immune system, such as AIDS, herpes, dengue fever, and some viral antigen-presenting cells. A wide range of hepatitis have been futile. Despite consider- viruses have been extensively studied for able efforts, no licensed vaccines have yet their potential as recombinant vaccines and been produced against any parasitic or fun- although each of them has its own unique gal human disease. These difficulties are characteristics, they all have the ability to caused by the failure to clearly define anti- induce not just humoral, but also cellular gen targets that induce specific and broad immune responses. combinations of cellular, humoral and mu- This review provides details on three cosal immune responses that can prevent viral vaccine vector systems (poxvirus, ad- infection and limit progression of the dis- enovirus, and alphavirus) receiving consid- ease, without the risk of using live, attenu- erable attention in the literature and consid- ated vaccines. Consequently, new technolo- ered by the authors as the most advanced. In gies are required to develop better and safer addition, two other promising viral vectors vaccines. (poliovirus and herpesvirus), still in the ini- Novel approaches require a much more tial stages of their development for use as detailed characterization of the genetic or- vaccine vectors, will be discussed briefly. ganization of the pathogen and the genes Some disadvantages of these systems will responsible for virulence or induction of also be discussed, and some potential solu- immunity. As a result of this increased knowl- tions on how to circumvent these shortcom- edge and ability to manipulate the genomes ings are offered. of pathogens, we are in an unprecedented position to develop better live vectored vac- Poxvirus cines that are safe and able to induce a wide range of protective immune responses in- Members of the Poxviridae family are cluding humoral and cellular immunity, as the most commonly used and best character- well as systemic and mucosal immunity. ized viral vectors for vaccine purposes. The Presently, two approaches have been widely success of the World Health Organization investigated: DNA vaccines and recombi- (WHO)’s smallpox eradication program nant viruses. DNA vaccines have been ex- through the use of vaccinia virus, along with tensively reviewed elsewhere (1). Recombi- the development of genetic manipulation nant viruses represent a particularly promis- techniques for these viruses, have led to the ing avenue of vaccine research, both for development of poxviruses as genetic vec- improving existing vaccines and for devel- tors for genes from many pathogenic organ- oping new ones. This process normally in- isms. These vectors were developed in the volves taking a proven safe and efficacious early eighties by cloning a foreign DNA into vaccine virus, such as vaccinia or adenovi- the genome of vaccinia virus, and the poten- rus, and modifying its genome to include tial of recombinant vaccinia viruses as vac- genes coding for immunogenic proteins from cine vectors was recognized immediately other pathogens. Virus-derived vectors offer after their development (2). several potential advantages over traditional Poxviruses are large viruses containing vaccine technologies. These include, most complex DNA genomes ranging in size be- notably, high-level production of protein tween 130 to 300 kb pairs with a hairpin loop antigens directly within cells of the immu- at each end (3). Although they are DNA nized host, potential adjuvant effects of the viruses, their replication occurs in the cyto- viral delivery system itself and the possibil- plasm of the infected cell due to the presence ity of efficient delivery of antigen directly to of a transcription machinery in the virions. Braz J Med Biol Res 38(4) 2005 Recombinant viruses as vaccines 511 The family Poxviridae is divided into two accept less than 5 kb of genetic material (4). subfamilies, one of which, Chordopoxviri- The possibility of introducing large amounts dae, comprises the poxviruses of vertebrates. of DNA without disrupting viral stability Chordopoxviridae consists of eight genera allows for the insertion of several antigens that are able to infect vertebrates; the genera even from different pathogens in the same Orthopoxvirus and Avipoxvirus have been recombinant vector, as has been shown with widely engineered to be used as recombinant the insertion of the hepatitis B virus surface vectors for vaccine purposes. Variola virus, antigen, the herpes simplex virus glycopro- the causative agent of smallpox, and vac- tein D and the influenza virus hemagglutinin cinia virus, used in the smallpox vaccine, in the same vaccinia vector that generated an belong to the genus Orthopoxvirus and immune response to all three transgenic pro- fowlpox and canarypox are two viruses be- teins upon injection in rabbits (5). longing to the genus Avipoxvirus. Recombinant technology utilizing vac- Certain characteristics make poxviruses cinia virus began around the time that the suitable for use as vaccine vectors. Impor- WHO declared smallpox eradicated in 1980 tantly, these vectors are very stable and, and recommended that the use of vaccinia when lyophilized, they can be refrigerated virus for vaccine purposes be discontinued. and used even after 2 months. They are easy Nevertheless, recombinant vaccinia vectors to manufacture at a low cost and, further- became an attractive tool for the study of the more, have the potential to be administered molecular biology of poxvirus for in vitro by different routes, as shown by their safe production of proteins and as a recombinant delivery by the intradermal, intranasal, intra- vaccine. The most useful strategy to make vaginal, and intrarectal routes to generate recombinant vaccinia vectors has been ho- antibody and T-cell responses. Oral admin- mologous DNA recombination within in- istration of vaccinia recombinants has been fected cells, a process that occurs naturally shown to generate both mucosal and sys- during viral replication. The use of plasmid temic immune responses to the recombinant vectors for DNA recombination which con- protein. Finally, preexisting immunity to vac- tain the complete expression