In vitro characterization of a simian immunodeficiency virus-human immunodeficiency virus (HIV) chimera expressing HIV type 1 reverse transcriptase to study antiviral resistance in pigtail macaques

Antiviral resistance is a significant obstacle in the treatment of human immunodeficiency virus type 1 (HIV-I)-infected individuals. Because nonnucleoside reverse transcriptase inhibitors (NNRTIs) specifically target HIV-1 reverse transcriptase (RT) and do not effectively inhibit simian immunodeficiency virus (SIV) RT, the development of animal models to study the evolution of antiviral resistance has been problematic. To facilitate in vivo studies of NNRTI resistance, we examined whether a SIV that causes immunopathogenesis in pigtail macaques could be made sensitive to NNRTIs. Two simian-human immunodeficiency viruses (SHIVs) were derived from the genetic background of SIVmne: SIV-RT-YY contains RT substitutions intended to confer NNRTI susceptibility (V181Y and L188Y), and RT-SHIVmne contains the entire HIV-1 RT coding region. Both mutant viruses grew to high titers in vitro but had reduced fitness relative to wild-type SIVmne. Although the HIV-1 RT was properly processed into p66 and p51 subunits in RT-SHIVmne particles, the RT-SHIVmne virions had lower levels of RT per viral genomic RNA than HIV-1. Correspondingly, there was decreased RT activity in RT-SHIVmne and SIV-RT-YY particles. HIV-1 and RT-SHIVmne were similarly susceptible to the NNRTIs efavirenz, nevirapine, and UC781. However, SIV-RT-YY was less sensitive to NNRTIs than HIV-1 or RT-SHIVmne. Classical NNRTI resistance mutations were selected in RT-SHIVmne after in vitro drug treatment and were monitored in a sensitive allele-specific real-time RT-PCR assay. Collectively, these results indicate that RT-SHIVmne may be a useful model in macaques for the preclinical evaluation of NNRTIs and for studies of the development of drug resistance in vivo.