Torquetenovirus Dynamics and Immune Marker Properties in Patients Following Allogeneic Hematopoietic Stem Cell Transplantation: A Prospective Longitudinal Study

Abstract Torquetenovirus (TTV) has been proposed as a marker of immune function in patients receiving immunosuppression after solid organ transplantation. This study aimed to define TTV plasma dynamics and investigate clinical associations in patients following allogeneic hematopoietic stem cell transplantation (HSCT). This was a single-center prospective longitudinal study involving 50 consecutive patients treated with HSCT between March 2015 and April 2016. TTV plasma DNA levels were measured with quantitative PCR at 12 consecutive time points during the first year after HSCT. Forty of the 50 patients (80%) had detectable TTV viremia before HSCT (median level, 5.37 log10 copies/mL; interquartile range [IQR], 3.51-6.44 log10 copies/mL). All patients subsequently developed TTV viremia during the follow-up period. Plasma viral loads evolved dynamically over time, with a peak of 8.32 log10 copies/mL (IQR, 7.33-9.35 log10 copies/mL) occurring at 79 days (IQR, 50-117 days) following HSCT and a stable plateau toward the end of the follow-up period. The type of malignancy, the use of antithymocyte globulin during conditioning, and the occurrence of acute graft-versus-host disease requiring systemic therapy had temporary effects on TTV dynamics. TTV levels showed a significant correlation with absolute lymphocyte counts following engraftment ( r s = -.27; P r s = .39; P r s = .45; P  = .02) viral loads during phases of viremia. Immune-related clinical events were not predicted by TTV levels. TTV viremia occurred universally and was sustained throughout the first year after HSCT. Several variables and events before and after HSCT were correlated with TTV levels and hint toward immune marker properties of TTV, but their complex interactions might perturb the capability of TTV to predict immune-related complications in this population.