Development of calibrated viral load standards for group M subtypes of human immunodeficiency virus type 1 and performance of an improved AMPLICOR HIV-1 MONITOR test with isolates of diverse subtypes

Accurate determination of plasma human immunodeficiency virus type 1 (HIV-1 ) RNA levels is critical for the effective management of HIV-1 disease. The AMPLICOR HIV-1 MONITOR Test, a reverse transcription-PCR-based test for qu antification of HIV-1 RNA in plasma, was developed when little sequence inf ormation on HIV-1 isolates from outside North America was available. It has since become apparent that many non-subtype B isolates, particularly subty pes A and E, are detected inefficiently by the test. We describe here the A MPLICOR HIV-1 MONITOR Test, version 1.5, an upgraded test developed to mini mize subtype-related variation. We also developed a panel of HIV-1 standard s containing 30 HIV-1 isolates of subtypes A through G. The virus particle concentration of each cultured viral stock was standardized by electron mic roscopic virus particle counting. We used this panel to determine the perfo rmance of the original AMPLICOR HIV-1 MONITOR Test and version 1.5 of the t est with HIV-1 subtypes A through G, The original test underestimated the c oncentration of HIV-1 subtype A E, F, and G RNA by 10-fold or more, whereas version of the 1.5 test yielded equivalent quantification of HIV-1 RNA reg ardless of the subtype. In light of the increasing intermixing of HIV-1 sub types worldwide, standardization of PCR-based tests against well-characteri zed viral isolates representing the full range of HIV-1 diversity will be e ssential for the continued utility of these important clinical management t ools,