Use of molecular beacons for rapid, real-time, quantitative monitoring of cytotoxic T-lymphocyte epitope mutations in simian immunodeficiency virus

Immune pressure on lentiviruses exerted by cytotoxic T lymphocytes (CTL) selects for virus CTL epitope mutations. Currently employed methods for monitoring emerging CTL epitope mutations rely on the labor-intensive and time-consuming techniques of virus population or clonal sequencing. Here we describe the development of a high-throughput quantitative reverse transcription-PCR assay that facilitates large-scale CTL epitope monitoring. This approach utilizes both sequence-specific molecular beacons and the sequence-independent double-stranded DNA binding dye Sybr Green. We show that this assay detects single-nucleotide mutations in an immunodominant CTL epitope in viral RNA isolated from both viral culture supernatants and plasma samples from simian immunodeficiency virus (STV)-infected rhesus monkeys. Furthermore, mutant viruses can be detected even when they represent as few as 500 mutant copies in a sample containing 10,000 total copies. This real-time PCR technique for evaluating CTL epitope mutations may prove to be a useful tool for monitoring the genetic drift of human immunodeficiency virus and SIV in infected individuals.