Kinetics of Alphatorquevirus plasma DNAemia at late times after allogeneic hematopoietic stem cell transplantation.

Torque teno virus (TTV) plasma DNA load has been consistently shown to be a surrogate biomarker of immunosuppression in solid organ transplant recipients. It is uncertain whether it may behave similarly in allogeneic hematopoietic stem cell transplant recipients (allo-HSCT). Here, we characterized the dynamics of TTV DNAemia in patients undergoing T-cell replete allo-SCT at late times after transplantation (> day + 100). This retrospective single-center observational study included 33 allo-HSCT patients. Plasma TTV DNA loads were quantified by real-time PCR before initiating the conditioning regimen and at different time points after transplant. Absolute lymphocyte counts (ALC) were measured by flow cytometry. Overall, TTV DNA load increased steadily after engraftment, reaching a peak by day + 90; afterwards, it remained relatively constant until day + 210. TTV DNA loads measured within days + 120 and + 210 correlated inversely with paired ALC, while both parameters did correlate directly within days + 20 and + 60. The median TTV DNA area under a curve between days + 90 and + 210 [(AUC)] was significantly higher in patients who received corticosteroids within this time frame for treatment of graft versus host disease (either acute, chronic or both) than in controls (P = 0.025). In summary, TTV DNA load may mirror the degree of immunosuppression at late times after allo-HSCT.