Plasma SIV RNA viral load determination by real-time quantification of product generation in reverse transcriptase-polymerase chain reaction.

Internally controlled RT-PCR methods (QC-RT-PCR) for quantification of SIV RNA are effective, but are relatively cumbersome, expensive, and time and labor intensive. For greater throughput and efficiency, we have developed a method for quantification of plasma SIV RNA levels by real-time RT-PCR using the Applied Biosystems Prism 7700 sequence detection system. This assay format allows real-time kinetic analysis of PCR product generation, providing a broad linear dynamic range and ensuring that quantification is based on analysis during the exponential phase of amplification, regardless of the input template copy number. Simultaneous amplification and analysis eliminates any requirement for handling amplified products, increasing throughput and eliminating a potential source of assay contamination. The assay we have developed for quantification of SIV RNA has a nominal threshold sensitivity of 300 copy Eq/ml of plasma, although as little as 10 copy Eq/reaction of SIV RNA template can be detected. The linear dynamic range is in excess of 5 logs. Interassay reproducibility averages 25% (coefficient of variation), based on studies of extraction and analysis of replicate aliquots of the same plasma specimens. The combination of sensitivity, precision, and broad dynamic range allows reliable quantification of viral load even during dynamic phases of SIV infection, such as through the onset and resolution of primary infection, or during treatment with antiretroviral agents. The primer-probe combinations we have developed allow quantification of SIV isolates most commonly used for experimental studies. Availability of this assay should greatly facilitate studies of basic pathogenesis and evaluation of therapeutic and prophylactic approaches in the SIV-infected macaque.