Quantification of the HIV-1 total reservoir in the peripheral blood of naïve and treated patients by a standardised method derived from a commercial HIV-1 RNA quantification assay.

ABSTRACT

OBJECTIVES: HIV-1 DNA can persist in host cells, establishing a latent reservoir. This study was aimed to develop an extraction and amplification protocol for HIV-1 DNA quantification by modifying a quantitative commercial assay. METHODS: HIV-1 DNA was extracted on an Abbott m2000sp instrument, using an open-mode protocol. Two calibrators, spiked with a plasmid containing HIV-1 genome (103 and 105 cps/mL), were extracted and amplified to generate a master calibration curve. Precision, accuracy, linear dynamic range, limit of quantification (LOQ) and limit of detection (LOD) were determined. A cohort of patients, naïve or chronically infected, was analysed. RESULTS: Calibration curve was obtained from 42 replicates of standards (stds); precision was calculated (coefficients of variability [CVs] below 10%); accuracy was higher than 90%. Linearity covered the entire range tested (10-104 copies per reaction), and LOD (95%) was 12 copies per reaction. HIV-1 DNA was significantly higher (p < 0.0001) in drug-naïve (62) than in chronically treated patients (50), and proviral loads correlated with lymphocytes (p = 0.0002) and CD4+ (p < 0.0001) counts only in naïve patients. Both groups displayed a significant inverse correlation between CD4+ nadir and proviral loads. A significant correlation (p < 0.0001) between viraemia and HIV-1 reservoir was disclosed. No significant difference was obtained from the comparison between proviral loads on whole blood and peripheral blood mononuclear cells (PBMCs) from the same patient. CONCLUSIONS: The novelty of our approach relies on the selection of appropriate reference standard extracted and amplified as clinical specimens avoiding any underestimation of the reservoir. Results confirm HIV-1 DNA as a marker of disease progression, supporting the relationship between the width of latent reservoir and the immunological status of the patient.