Post-transplant Replication of Torque Teno Virus in Granulocytes.

Karin Kosulin,Silvia Kernbichler,René Geyeregger,Thomas Lion,Anita Lawitschka,Volker Witt,Herbert Pichler

doi:10.3389/fmicb.2018.02956

Abstract

Torque Teno virus (TTV) in humans is characterized by ubiquitous occurrence in peripheral blood (PB), without any related disease described to date. Several studies reported a significant increase of TTV plasma DNA levels in allogeneic transplant recipients, and suggested a correlation of elevated virus titers with immunosuppression and transplant-related complications. However, the site of viral replication in this setting has remained unclear. We have studied TTV in serial plasma specimens derived from 43 pediatric allogeneic hematopoietic stem cell transplantation (HSCT) recipients by RQ-PCR, and found increasing TTV-DNA levels in all patients post-transplant, with a peak around day +100 and maximum virus copy numbers reaching 4 × 10E9/ml. To assess whether the virus replicates in PB-cells, leukocyte subsets including granulocytes, monocytes, NK-cells, T- and B-lymphocytes were serially isolated by flow-sorting for TTV analysis in 19 patients. The virus was undetectable in most cell types, but was identified in granulocytes in all instances, revealing a median DNA copy number increase of 1.8 logs between days +30–100 post-transplant. Our data therefore provide evidence for TTV replication in granulocytes in this setting. In a control cohort of immunocompetent children and in HSCT recipients before day +30, TTV positivity in granulocytes was less common (33%), and the copy numbers were considerably lower. However, rising TTV replication about 2 weeks after granulocyte engraftment (>500 cells/μl) was observed suggesting that granulocyte recovery might be required for TTV expansion in severely immunosuppressed transplant recipients.

Highlights

Torque Teno Virus (TTV) was first discovered in 1997 in a patient with hepatitis of unknown etiology (Nishizawa et al, 1997), and was assigned to the family of Anelloviridae (Maggi and Bendinelli, 2009; Spandole et al, 2015)
To address the possibility that post-transplant replication of TTV occurs in specific nucleated blood cells, different leukocyte resulted in false-positive test results for individual leukocyte fractions, low-level positivity below 2% of the TTV DNA copy numbers detected in leukocyte subsets other than granulocytes was regarded as a negative result
To assess whether the observed TTV replication in granulocytes of pediatric hematopoietic stem cell transplantation (HSCT) recipients might correlate with transplantindependent persistence of the virus in peripheral blood (PB), targeted testing was performed in a control cohort of 30 hospitalized children with non-malignant diseases who were no candidates for allogeneic stem cell transplantation

Summary

Introduction

Torque Teno Virus (TTV) was first discovered in 1997 in a patient with hepatitis of unknown etiology (Nishizawa et al, 1997), and was assigned to the family of Anelloviridae (Maggi and Bendinelli, 2009; Spandole et al, 2015). 34 of the 43 pediatric HSCT patients investigated (79%) had the virus detectable in plasma already before transplantation, and all patients tested positive for TTV DNA by day +50 post-transplant, as revealed by RQ-PCR analysis.

Results

Conclusion