Torque teno virus loads and leukocyte populations in stable outpatient solid organ transplant recipients

Torque teno virus (TTV) is proposed as a biomarker of immune function, potentially aiding in personalized immunosuppressive dosing after solid organ transplantation. TTV is thought to replicate in leukocytes, particularly immature granulocytes. We primarily aimed to assess the association between immature granulocyte count and TTV load, while also exploring associations between TTV load and other leukocyte populations.

A total of 701 SOTR at 3 months post-transplantation were included from the TransplantLines Study for cross-sectional analyses. TTV load was measured by PCR assay (TTV R-GENE®, bioMérieux) and leukocytes were counted by a Sysmex XN hematology analyzer. Linear regression analyses were performed to assess associations.

The mean age of the cohort was 57.0 ± 13.4 years, and 35.8% were female. In multivariable regression analyses, after adjusting for factors known to potentially influence TTV load, immature granulocyte count was positively associated with TTV load (st.β = 0.45, P < 0.001), while total granulocyte count was negatively associated (st.β=-0.39, P < 0.001).

These results provide evidence to support the theory that TTV replicates in immature granulocytes. The negative association with total granulocyte count suggests possible antiviral effects or altered granulocyte lifespan. These relationships may help clinical interpretation of TTV as a marker of immune function.