Figure 1: Alphavirus vectors applied in vaccine development. A. Naked RNA vector: In vitro transcribed RNA is directly injected into animals. B. Replication- deficient recombinant particles: Replicon particles are obtained from in vitro transcribed RNA from expression and helper vectors after co-electroporation of BHK-21 cells. C. Layered DNA vectors: Plasmid DNA can be used directly for immunization.