Torque teno virus as a marker of immune status in immunocompromised patients: A systematic review

Torque teno virus (TTV) is not known to cause disease in humans; however, chronic inflammatory conditions and immunosuppression states can favour TTV replication. This study aimed to verify the effectiveness of TTV as an immune biomarker.

The protocol of this review was registered in PROSPERO (CRD42022331049) and performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

Thirty-three articles were selected and different groups of patients were assessed. In the solid organ and hematopoietic stem cell transplant groups, most studies reported that TTV viral load (VL) was highly detectable after transplantation and compared to controls, but the association with immune parameters showed conflicting results. In melanoma patients, no statistical difference in TTV VL was identified between susceptible and treatment-resistant patients. In lung cancer patients, viral load increases significantly with disease progression but decreases after chemotherapy. HIV-positive patients showed a higher VL than controls, but an inverse correlation with CD4+ was observed in half of the studies. Although 57.14% of all studies presented a low risk of bias, significant differences were observed between studies, particularly in the choice of the analyzed outcome, the parameter used to evaluate the patient's immune status, the presence of a control group, and the sample collection time points.

Although TTV seems to have the potential to be a promising biomarker of immunosuppression, further high-quality prospective clinical studies are still needed.