The invention provides a DNA plasmid comprising: (a) a first transcriptional unit comprising a nucleotide sequence that encodes a first polypeptide operably linked to regulatory elements including a first promoter and a first polyadenylation signal； (b) a second transcriptional unit comprising a nucleotide sequence that encodes a second polypeptide operably linked to regulatory elements including a second promoter and a second polyadenylation signal； (c) a third transcriptional unit comprising a nucleotide sequence that encodes a third polypeptide operably linked to regulatory elements including a third promoter and a third polyadenylation signal； and wherein said first, said second and said third promoters are each derived from different transcriptional units； and wherein said first, said second and said third polyadenylation signals are each derived from different transcriptional units. The invention further relates to immunogenic compositions for inducing an immune response to HIV comprising combinations of two, three, or four plasmids, where each plasmid is expressing a defined antigen, which may be a single antigen or a fusion of two or three antigens.
