# Evaluation of Torquetenovirus (TTV) Particle Integrity Utilizing PMAxx™

## TL;DR

This study evaluates how PMAxx™ improves the accuracy of measuring Torquetenovirus (TTV) DNA by reducing overestimation from non-intact particles.

## Contribution

The study introduces PMAxx™ as a method to enhance the specificity of TTV DNA quantification in clinical samples.

## Key findings

- PMAxx™ treatment significantly reduced TTV DNA levels across all groups, indicating many non-intact viral particles.
- There was no strong correlation between TTV DNA levels and SARS-CoV-2 antibody responses after vaccination.
- PMAxx™ improved TTV quantification specificity but did not enhance its predictive value for vaccine-induced immunity.

## Abstract

Torquetenovirus (TTV) is a ubiquitous, non-pathogenic DNA virus that has been suggested as a biomarker of immune competence, with the viral load correlating with the level of immunosuppression. However, by detecting non-intact viral particles, standard PCR-based quantification may overestimate the TTV viremia. To improve the clinical relevance of TTV quantification, in this study, we investigated the use of PMAxx™, a virion viability dye that selectively blocks the amplification of compromised virions. Serum samples from 10 Hepatitis C Virus-positive (HCV+) individuals, 81 liver transplant recipients (LTRs), and 40 people with HIV (PWH) were treated with PMAxx™ and analyzed for TTV DNA loads by digital droplet PCR (ddPCR). Furthermore, anti-SARS-CoV-2 IgG levels and neutralizing antibody (nAbs) titers were measured post-COVID-19 vaccination. Using ddPCR, the PMAxx™ treatment significantly reduced the TTV DNA levels in all the groups (mean reduction: 0.66 Log copies/mL), indicating the abundant presence of non-intact, circulating viral genomes. However, correlations between TTV DNA and SARS-CoV-2 IgG or nAbs were weak or absent in both PMAxx™-treated and untreated samples. These findings suggest that while PMAxx™ enhanced the specificity of TTV quantification, it did not improve the predictive value of TTV viremia at assessing vaccine-induced humoral responses.