Herpes viruses and tumours in kidney transplant recipients. The role of immunosuppression

Herpes virus infections are frequent in renal transplant recipients. Some herpes viruses are not only responsible for life-threatening infections and renal graft injury but can also increase the risk of malignancy. Three herpes viruses, namely cytomegalovirus (CMV) or human herpes virus 5, Epstein-Barr virus (EBV) or herpes virus 4 and human herpes virus 8 (HHV8), may play an oncogenic role. The oncogenic role of CMV is controversial. However, there is growing evidence showing that CMV can infect cancer cells and favour their resistance to the immune system and chemotherapy. B cells infected by EBV can have uncontrolled proliferation eventually resulting in polyclonal polymorphic or monomorphic post-transplant lymphoproliferative diseases (PTLD), which are particularly frequent in children and in EBV-negative recipients. In some ethnicities, the carriers of HHV8 are susceptible to develop Kaposi's sarcoma after transplantation. The intensity of immunosuppression therapy plays a critical role in mediating infections from oncogenic herpes viruses. However, the type of immunosuppressive drugs can also influence the risk of virus-mediated neoplasias. An aggressive induction therapy aimed at depleting lymphocytes may favour the reactivation and dissemination of oncogenic herpes viruses, while anti-CD25 monoclonal antibodies have little impact on virus reactivation. Calcineurin inhibitors can increase the risk of viral infections and malignancy. Mycofenolate salts may perhaps protect from EBV-related PTLD. Finally, the inhibitors of the mammalian target of rapamycine may reduce the risk of viral disease by inhibiting the cascade of kinases that govern the proliferation and replication of oncogenic herpes viruses.