Recombinant, chimeric, live, attenuated vaccines against flaviviruses and alphaviruses

Abstract

Many arthropod-borne flaviviruses are important human pathogens responsible for diverse illnesses, including yellowfever (YF), Japanese encephalitis (JE), and TBE and dengue. Live, attenuated vaccines have afforded the most effective and economical means of prevention and control, as illustrated by YF 17D and JE SA14-14-2 vaccines. Recent advances in recombinant DNA technology have made it possible to explore a novel approach for developing live attenuated flavivirus vaccines against other flaviviruses. Full-length cDNA clones allow construction of infectious virus bearing attenuatingmutations or deletions incorporated in the viral genome. It is also possible to create chimeric flaviviruses in which the structural protein genes for the target antigens of a flavivirus are replaced by the corresponding genes of another flavivirus. By combining these molecular techniques, the DNA sequences of DEN4 containing a deletion in the 30NCR, a DEN2 PDK-53 candidate vaccine and YF 17D vaccine have been used as the genetic backbone to construct chimeric flaviviruseswith the required attenuation phenotype and expression of the target antigens. Encouraging results from preclinical and clinical studies have shown that several chimeric flavivirus vaccines have the safety profile and satisfactory immunogenicity and protective efficacy to warrant development as products for human use. The chimeric flavivirus strategy has led to the rapid development of novel live, attenuated vaccines against DEN, TBE, JE and WN. This chapter reviews an extensive body of work on the development of these vaccine candidates, one of which is licensed and others are in advanced clinical development. A similar approach is being used to create vaccines against alphaviruses. Here the experience is less, but some promising data have been developed, particularly using SIN virus as a vector for structural genes of heterologous alphaviruses. The principal issues for this technology will be to achieve convincing nonclinical data on safety, the proper balance of attenuation and immunogenicity, and proof of concept in large animal models and ultimately humans. © Springer Basel AG 2011.