Improved genetic stability of recombinant yellow fever 17D virus expressing a lentiviral Gag gene fragment

•The YF 17D virus expressing part of the SIV Gag 45-269 protein fragment was genetically unstable.•The viral genetic stability was reached by mutating the IRES element localized in the gag gene fragment.•These genetic changes did not alter the rates of viral growth or immunogenicity in a mouse model.

We have previously designed a method to construct viable recombinant Yellow Fever (YF) 17D viruses expressing heterologous polypeptides including part of the Simian Immunodeficiency Virus (SIV) Gag protein. However, the expressed region, encompassing amino acid residues from 45 to 269, was genetically unstable. In this study, we improved the genetic stability of this recombinant YF 17D virus by introducing mutations in the IRES element localized at the 5' end of the SIV gag gene. The new stable recombinant virus elicited adaptive immune responses similar to those induced by the original recombinant virus. It is, therefore, possible to increase recombinant stability by removing functional motifs from the insert that may have deleterious effects on recombinant YF viral fitness.