The invention generally relates to recombinant polynucleotides, positive-strand
RNA virus (psRNAV) recombinant expression vectors, and packaging systems. The packaging
systems are based on the expression of helper functions by coinfecting recombinant
poxvirus vectors comprising recombinant polynucleotides. Methods for obtaining
psRNAV replicon particles using these packaging systems are disclosed. Immunogenic
compositions and pharmaceutical formulations are provided that comprise replicon
particles of the invention. Methods for generating an immune response or producing
a pharmaceutical effect are also provided.