Background

Human T-lymphotrophic virus (HTLV) types 1 and 2 cause lifelong infection whereby most infected individuals are asymptomatic whilst a minority develop infection-related disease. These latter patients invariably have been found to have high proviral load (PVL). Therefore, infected patients are monitored by determining the proportion of lymphocytes that are infected with HTLV-1/2. An increase in PVL has been shown to represent an increasing risk of developing HTLV-associated diseases. Monitoring of PVL requires a reliable and sensitive method. In this study assays based on droplet digital PCR (ddPCR) were established and evaluated for detection and quantification of HTLV-1/2.
Objectives

To develop two parallel assays to detect the tax genes and determine the PVL of HTLV-1 and -2.
Study design

Sixty-seven clinical samples from patients infected with HTLV-1 or HTLV-2 were analysed. The samples had previously been analysed with a qPCR and a comparison between ddPCR and qPCR was performed. The specificity of the assays were determined by analyzing samples from 20 healthy blood donors.
Results

The ddPCR was a stable and sensitive method for detection and quantification of HTLV-1 and -2. When comparing the qPCR and ddPCR the correlation was high (Pearsons correlation coefficient 0.96). The variability of the ddPCR was very low with intra-assay coefficient of variation (CV) of 0.97–3.3% (HTLV-1) and 1.7–8.2% (HTLV-2) and inter-assay CV of 1.8–6.1% (HTLV-1) and 1.2–12.9% (HTLV-2).
Conclusions

The ddPCR reliably quantified HTLV DNA in clinical samples and could be a useful tool for monitoring of PVLs in HTLV-infected individuals.