Quantitative Analysis of Human Herpesvirus 8 Viral Load Using a Real-Time PCR Assay

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Abstract
We have developed a quantitative real-time PCR (TaqMan) assay aimed at measuring the cellular human herpesvirus 8 (HHV-8) DNA load in various clinical samples. Standard curves were obtained by serial dilutions of a control plasmid containing both HHV-8 (ORF73 gene) and the cellular target (human albumin gene). The assay appeared to be very sensitive (100% detection rate for at least 10 copies per well) and specific and was easily reproducible (less than 3% intra-assay variability, 5% interassay variability). This method allowed us to quantify precisely the average HHV-8 copy number per cell in various persistently HHV-8-infected cell lines (BBG-1 cells, n = 200; BC-1 cells, n = 59; BCBL-1 cells, n = 70). A retrospective study was also conducted to assess the HHV-8 DNA load in 12 human immunodeficiency virus-infected patients with either Kaposi's sarcoma (KS; seven patients monitored over a 3-month period) or multicentric Castleman's disease (MCD; five patients). The HHV-8 DNA load ranged from 0 to 9,171 copies/10 6 cells in low-risk KS patients (T0, I0, S0 according to the classification of the AIDS Clinical Trials group). We also measured the viral loads in MCD patients either during symptomatic periods or during remission. The results are in agreement with previously published data, with high viral loads correlating with clinical symptoms (1.3 × 10 6 copies/10 6 cells) and low viral loads correlating with asymptomatic periods (less than 5,000 copies/10 6 cells).