Introduction: BK polyomavirus (BKV) replication can be detected in up to 60% of kidney transplant recipients, with an incidence of nephropathy of 5-10%, leading to graft loss in as many as 70% of cases. An early therapeutic intervention, reducing immunosuppression, is key in these cases. mTOR inhibitors (mTOR-I) can play an important role due to their antiviral effect.
Material and Methods: This retrospective study with a longitudinal follow-up included 20 recipients of a kidney transplant between February 2014 and September 2016. After detecting BKV replication the MMF was replaced by an mTOR-I with minimization of tacrolimus. The course of their clinical and laboratory variables was analysed during the follow-up period.
Results: The mean age of the patients was 55±14 years (80% male) and that of the donors was 58±13 years (50% male); 30% had had a previous transplant. All had received triple therapy with tacrolimus, MMF and prednisone; 85% received induction (six patients with anti-CD25 and 11 thymoglobulin). At the time of conversion (17±6 weeks post-transplant), all had BK viruria and 17 also had viremia. A kidney biopsy was done in 14 patients due to suspected nephropathy (BKVN), confirming the diagnosis in 11. The median postconversion follow-up period was 22±6  months. During this period two patients with BKVN lost graft function. The others conserved stable kidney function at 12 months  postconversion  (baseline MDRDa: 37±12 vs 1 year: 36±18 ml/min; p=0.7). During follow-up the viremia had become negative in 76% of the patients and the viruria in 50%. No adverse effects attributable to the mTOR-I were noted, except  for one patient who required withdrawal due to diarrhea. There were one episode of acute rejection.
Conclusions: Early conversion to treatment based on low doses of tacrolimus and a mTOR-I in patients who develop BKV replication is an efficient and safe strategy, providing adequate control of the infection and very good graft survival, even in patients who develop BKVN.