Surveillance of polyomavirus BK in relation to immunosuppressive therapy in kidney transplantation

Introduction. Reactivation of polyomavirus BK in kidney transplant recipients has been associated to the development of nephropathy (polyomavirus-associated nephropathy, PVAN), possibly leading to the loss of the transplanted organ. Immunosuppression is the condicio sine qua non for the onset of PVAN; however, a lower incidence of BK viremia has been reported with low-level tacrolimus based immunosuppressive protocols in comparison to cyclosporine A.Aim of this study was to compare the two immunosuppressive protocols. Methods. Virological monitoring of BK was performed in 468 consecutive renal transplant patients over a period of 3 years (2370 urine e 2370 serum specimens): in particular, 1780 specimens from 362 patients treated with tacrolimus and 590 from 106 treated with cyclosporine A. Results. BK viremia was evidenced in 124 (7.0%) and 12 (2.0%) specimens from 40 (11.0%) and 11 (10.4%) patients treated with tacrolimus and cyclosporine A, respectively; similarly, BK viruria in 289 (16.2%) and 58 (9.8%) specimens from 67 (18.5%) and 27 (25.5%) patients, being the difference of incidence highly significant (p <0.0001) for both viremia and viruria at comparison between specimens and not significant for patients. No case of PVAN was diagnosed at histophatology evaluation. Conclusions. The incidence of viremia and viruria was similar to that previously reported. Our results evidenced that with low-level tacrolimus-based protocols the overall incidence of reactivation in renal transplant patients is not significantly different and there is no increased risk of PVAN, nevertheless the higher incidence of episodes of reactivation.