A novel codon-optimized SIV gag-pol immunogen for gene-based vaccination

Catherine M Crosby,Eric A Weaver,Reeti Khare,Zenaido T Camacho,Michael A Barry

doi:10.1016/j.virep.2015.03.002

Catherine M Crosby, Eric A Weaver + Show 3 more

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https://doi.org/10.1016/j.virep.2015.03.002

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Abstract

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 gag-pol encodes many epitopes with potential to drive multivalent T cell responses. While it is an attractive antigen, pol is only translated after a frame shift from gag so that only 1 in 10 gag proteins include this larger antigen. 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.

Highlights

Vaccines are the most economical medical intervention to control infectious agents, yet traditional vaccine strategies have struggled to control some of the more difficult pathogens (reviewed in (Barry, 1999))
The self-cleaving sequences were inserted into Simian immunodeficiency virus (SIV) gag-pol fusion with two identical restriction sites flanking each as follows: P2A was flanked by AfeI sites, E2A was flanked by BbvCI sites, T2A was flanked by SpeI sites, and F2A was flanked by XhoI sites
The fusion protein without cleavage sequences generated stronger T cell responses than the cleaved construct. This antigen engineering study was motivated by the pragmatic need for a codon-optimized SIV gag-pol expression construct for vaccine testing

Summary

Introduction

Vaccines are the most economical medical intervention to control infectious agents, yet traditional vaccine strategies have struggled to control some of the more difficult pathogens (reviewed in (Barry, 1999)). The host cell becomes a factory to produce the protein vaccine This in situ intracellular production of pathogen proteins from a plasmid produces antibodies, and allows protein display on Major Histocompatibility Complex (MHC) I and II molecules on the host cells. This MHC I display of genetic vaccine proteins drives CD4 and CD8 T cell responses that are important to kill intracellular pathogens. Based on this, genebased vaccines have been extensively applied against human immunodeficiency virus (HIV-1) and against its models simian immunodeficiency virus (SIV), and SIV-HIV chimeras (SHIVs) (reviewed in (Barry, 2012)

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