A new study demonstrates that the immunosuppressive drug Tacrolimus directly activates the replication of the BK polyomavirus and could be responsible for these complications after kidney transplant. The American Journal of Transplantation has published the study, which was conducted by the research group of Professor Hans H. Hirsch from the Department of Biomedicine at the University of Basel.

Polyomavirus infections are common, but they usually do not cause symptoms in healthy adults. However, the virus becomes much more problematic for patients who have to take immunosuppressive drugs after kidney transplantation. In 10 to 20% of all cases, the BK virus starts to spread within the transplant and causes an inflammation. This can, in the worst case, destroy the new organ entirely and put the patient back on the transplant waiting list.

Drugs affect virus differently

The Transplantation & Clinical Virology research group from the Department of Biomedicine at the University was now able to show, that the BK virus reacts completely different to various immunosuppressive drugs: While the commonly used drug Tacrolimus activates the replication of the virus inside kidney cells, the substance Sirolimus, a mTOR inhibitor, inhibits virus replication.

The results explain why in the past ten years an increasing number of cases of BK polyomavirus complications have occurred after the widespread introduction of Tacrolimus in transplantation clinics. The findings also provide important rationales for clinical trials in order to test the use of mTOR inhibitors like Sirolimus in patients in acute danger of loosing their kidney transplant without simultaneously having to increase the risk of organ rejection, according to the study authors.