Large-scale nucleotide optimization of simian immunodeficiency virus reduces its capacity to stimulate type I interferon in vitro.

UNLABELLED: Lentiviral RNA genomes present a strong bias in their nucleotide composition with extremely high frequencies of A nucleotide in human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV). Based on the observation that human optimization of RNA virus gene fragments may abolish their ability to stimulate the type I interferon (IFN-I) response, we identified the most biased sequences along the SIV genome and showed that they are the most potent IFN-I stimulators. With the aim of designing an attenuated SIV genome based on a reduced capacity to activate the IFN-I response, we synthesized artificial SIV genomes whose biased sequences were optimized toward macaque average nucleotide composition without altering their regulatory elements or amino acid sequences. A synthetic SIV optimized with 169 synonymous mutations in gag and pol genes showed a 100-fold decrease in replicative capacity. Interestingly, a synthetic SIV optimized with 70 synonymous mutations in pol had a normal replicative capacity. Its ability to stimulate IFN-I was reduced when infected cells were cocultured with reporter cells. IFN regulatory factor 3 (IRF3) transcription factor was required for IFN-I stimulation, implicating cytosolic sensors in the detection of SIV-biased RNA in infected cells. No reversion of introduced mutations was observed for either of the optimized viruses after 10 serial passages. In conclusion, we have designed large-scale nucleotide-modified SIVs that may display attenuated pathogenic potential. IMPORTANCE: In this study, we synthesized artificial SIV genomes in which the most hyperbiased sequences were optimized to bring them closer to the nucleotide composition of the macaque SIV host. Interestingly, we generated a stable synthetic SIV optimized with 70 synonymous mutations in pol gene, which had a normal replicative capacity but a reduced ability to stimulate type I IFN. This demonstrates the possibility to rationally change viral nucleotide composition to design replicative and genetically stable lentiviruses with attenuated pathogenic potentials.