A Novel Codon-optimized SIV Gag-pol Immunogen for Gene-based Vaccination.

Simian immunodeficiency virus (SIV) is a robust pathogen used in non-human primates to model HIV vaccines. SIV encodes a number of potential vaccine targets. By far the largest and most conserved protein target in SIV is its gag-pol protein that bears many epitopes to drive multivalent immune T cell responses. While gag-pol is an attractive antigen, it is only translated after a frame shift between gag and pol with the effect that gag and pol are expressed at an approximate 10/1 ratio. The codon bias of native lentiviral genes are also mismatched with the abundance of tRNAs in mammalian cells resulting in poor expression of unmodified SIV genes. To provide a better SIV gag-pol immunogen for gene-based vaccination, we codon-optimized the full gag-pol sequence from SIVmac239. To increase pol expression, we artificially moved the pol sequence in frame to gag to bypass the need for a translational frame shift for its expression. Finally, we inserted four "self-cleaving" picornavirus sequences into gag p24, protease, reverse transcriptase, and into integrase to fragment the proteins for potentially better immune presentation. We demonstrate that these immunogens are well expressed in vitro and drive similar antibody and T cell responses with or without cleavage sequences.