Transient allograft dysfunction from immune reconstitution in a patient with polyoma BK-virus-associated nephropathy.

During the last 10 years, polyoma BK-virus associated nephropathy (PVAN) has emerged as a serious complication in renal transplant recipients [1]. Due to the establishment of an accurate non-invasive screening procedure measuring polyomavirus BK-viraemia, BK-viruria and decoy cells in urine, PVAN can be diagnosed at early stages [2]. This allows for timely therapeutic intervention, which has significantly reduced the incidence of severe PVAN courses including graft loss [3,4]. Management of PVAN is mainly based on a reduction of the immunosuppressive drugs, while the impact of anti-viral therapy is not yet clear [5]. This strategy bears the inherent risk that allograft rejection may arise, which is difficult to differentiate from an immune response to the BK-virus, because both entities can present as morphologically and molecularly indistinguishable, with interstitial infiltrates and tubulitis [1,5–7]. Therefore, more data regarding the natural course of PVAN under reduced immunosuppression might be helpful to illuminate the scope of post-intervention responses.