Recombinant simian immunodeficiency virus expressing green fluorescent protein identifies infected cells in rhesus monkeys

We engineered recombinant derivatives of simian immunodeficiency virus (SIV ) to express enhanced green fluorescent protein (EGFP). Replacement of vpr sequences with EGFP resulted in a genome that did not produce detectable le vels of replication-competent virus. Replication-competent virus and bright fluorescence of infected cells were obtained with two other constructs, on e in which SIV nef sequences were replaced by EGFP and another in which EGF P was inserted into the SIV nef locus and HIV-1 nef sequences were expresse d by downstream placement of an internal ribosomal entry site. These strain s were infectious in rhesus monkeys and green fluorescing cells were detect ed in the tissues of infected monkeys by FAGS analysis and by direct micros copic visualization. EGFP sequences were absent from recovered virus by 8 w eeks following infection. We conclude that recombinant SIV that is engineer ed to express EGFP can be used to directly detect productively infected cel ls and aid in the immunophenotypic characterization of these cells within t he first 2 weeks of infection of rhesus monkeys.