Alphavirus hybrid virion vaccines.

Many members of the alphavirus family are important human or veterinary pathogens. These viruses are extremely similar in molecular architecture yet differ in host range and in the pathological consequences of infection. Despite marked structural conservation, the various species are inefficient in eliciting immunological cross protection. Previously(l) we described a systematic approach for selection of epitope-cassettes of the E2 envelope of the alphavirus family that induce virus species specific protective immunity. This approach was tested and proved successful(2–5) with two viruses - Sindbis (SIN) and Semliki Forest (SF) - which are very remote phylogenetically. Vaccination was performed with recombinant peptide cassettes fused to a bacterial protein carrier (β-galactosidase) formulated with different adjuvants. In order to create a vaccine compatible with human use, we designed several live vector vaccines for presentation of the protective epitope cassette. Attenuated salmonella vaccine vector which can potentially allow presentation of many different cassettes and thus generation of a pan-alphavirus vaccine, proved to be inefficient. On the other hand the live attenuated viral vaccine based on a benign alphavirus such as SIN vector, appears to be promising. The principle of such vaccines is substitution of E2 epitopes of SIN virus vector with parallel protective epitopes from a different alphavirus. This system should have the advantage of presentation of specific virus epitopes in the context of the SIN alphavirus backbone which in turn could provide cross protective immunity on the basis of multiple common antigen determinants.