| The live attenuated Oka vaccine is safe and effective for the prevention of primary disease caused by varicella zoster virus (VZV), which causes chickenpox (varicella) and shingles (herpes zoster) in humans. However, several problems concerning the vaccine still exist. The molecular basis of attenuation is unknown, vaccine lots are polygenic, and the vaccine is able to reactivate in humans to cause shingles. Evaluation of candidate second-generation VZV vaccines is hindered by the lack of an appropriate animal model in which to study pathogenesis, immunogenicity, and reactivation of engineered viruses. Simian varicella virus (SVV) is a closely related alphaherpesvirus of nonhuman primates, causing varicella- and zoster-like diseases in animals and offering a model system in which to evaluate potential vaccine strains.; Using molecular cloning techniques, recombinant SVV (rSVV) viruses were engineered by deleting genes potentially involved in pathogenesis, latency and/or reactivation. Viral genes involved in DNA replication and nucleotide metabolism were targeted, specifically the deoxyUTPase (SVV gene 8), the UNG (SVV gene 59), and the ribonucleotide reductase (large subunit, SVV gene 19). Furthermore, viral regulatory genes including the transactivator gene 61 and the latency-associated transcript were targeted in attempts to attenuate the virus, particularly with regard to latency. PCR and RT-PCR analyses confirmed deletion of viral genes, and in vitro characterization of rSVVs confirmed their viability.; The Oka vaccine is an attractive vector for the delivery of antigens from unrelated pathogens, as a strategy to protect against other diseases. Respiratory syncytial virus (RSV) is the most important viral respiratory pathogen of infants, and is also a major pathogen of the elderly and immunocompromised; to date, no successful vaccine exists. rSVV viruses were engineered to express the G glycoprotein and M2 second matrix protein from RSV, in order to form bivalent vaccines. Immunofluorescence and western blot assays confirmed the expression of RSV antigens by rSVV vaccines, and viruses were viable in vitro. Rhesus macaque monkeys were immunized with rSVV-RSV recombinant viruses, and exhibited humoral immune responses to both the SVV vector and to the RSV trans-antigens.; The results of these genetic studies using SVV reveal several potential strategies toward improvement of varicella vaccines. Defined attenuation mutations, clonal vaccine strains, and bivalent vaccines are exciting avenues of research that may lead to the next generation of vaccination against VZV and other pathogens. |
