Torque-Teno virus viral load as a potential endogenous marker of immune function in solid organ transplantation

Solid organ transplantation (SOT) recipients receive immunosuppressive therapy to avoid rejection of the transplanted organ. Immunosuppressive therapy increases the risk of infections. However, no existing marker reliably reveals the status of the immune function in SOT recipients. Torque-Teno virus or Transfusion-transmitted virus (TTV) has gained attention as a possible endogenous marker of the immune function. TTV is a non-enveloped, circular single strand DNA virus, and it may be considered a part of the human virome. In a bidirectional relationship, the immune system detects TTV and TTV may also modulate the activity of immune system. These characteristics have made the virus a possible candidate indicator of immune function. In this systematic review, we describe the role and potential function of TTV viral load as an endogenous marker of the immune function and consequently the level of immune suppression in SOT recipients. •This systematic review includes evidence regarding the ability of TTV to predict infection or rejection in SOT recipients.•The choice of assay to determine TTV viral load impacts the results and in future studies the assay should be standardized.•At present there is not sufficient data to support a role for TTV as an accurate marker of immunesuppression or -activation.•Future prospective studies should focus on the impact of different types of immunosuppressants and include healthy controls.