Development of a Standardized Real Time PCR for Torque Teno Viruses (TTV) Viral Load Detection and Quantification: A New Tool for Immune Monitoring

Background: Torque teno viruses (TTV) are small DNA viruses whose replication is closely linked to immune status. A growing number of publications underlined the potential of TTV viral load as an indicator of immunosuppression.

Objectives: To demonstrate the analytical performance of the first standardized RUO (Research Use Only) assay to detect and quantify human TTV DNA in whole blood and plasma.

Study Design: We established analytical performances for TTV load measurement in various populations. The TTV kinetics were followed in kidney recipients. TTV viral load was analyzed on whole blood samples from 42 kidney recipients follow-up, 53 kidney deceased donors and 31 healthy volunteers.

Results: The qPCR TTV assay detects the most prevalent human TTV genotypes and does not cross react with other viruses. Limit of detection was 2.2 log copies/mL in whole blood and plasma, linearity and precision were demonstrated over the range 1.61 to 10.61 log copies/mL in whole blood. Prevalence of TTV DNA in blood differed significantly among groups: 45% in healthy volunteers, 74% in donors and 83% in kidney recipients. In kidney recipients, early TTV kinetics were comparable to those previously observed with in-house assays in other transplant settings: viral load increased from an average of 4.3 log to 7.9 log copies/mL within the first 75 days post transplantation.

Conclusion: This TTV assay showed high analytical sensitivity, specificity, linearity and precision. It is a useful standardized tool to further evaluate TTV load as a biomarker of immune status that could improve individual treatment strategy.