{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T16:28:20Z","timestamp":1791563300713,"version":"4.3.4"},"reference-count":63,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,7,6]],"date-time":"2026-07-06T00:00:00Z","timestamp":1783296000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Med."],"abstract":"<jats:p>BK polyomavirus\u2013associated nephropathy (BKPyVAN) results from primary infection or reactivation of BK polyomavirus (BKPyV) and remains a significant complication in kidney transplant recipients, contributing to allograft dysfunction and premature allograft loss. Most cases occur within the first 2 years post-transplant, when cell-mediated immunity is most suppressed due to induction immunosuppression. Here, we describe two unusual cases of late-onset BKPyVAN occurring in the absence of intensified immunosuppression and provide a review of potential mechanisms underlying its development in kidney transplant recipients. In the first patient, BKPyVAN developed 9 years after transplantation during maintenance dual immunosuppression with tacrolimus and mycophenolic acid, without prior rejection episodes or exposure to intensified immunosuppression. In the second patient, BKPyVAN first occurred 3 years post-transplant in the setting of concomitant cytomegalovirus colitis, also during dual immunosuppression with tacrolimus and mycophenolic acid. Despite reduction of immunosuppression, BKPyVAN persisted at 1-year follow-up and was associated with a gradual decline in allograft function. These cases highlight that late-onset BKPyVAN may develop even without intensified immunosuppression and can lead to significant allograft injury. Improved strategies are needed to identify patients at risk for late-onset BKPyVAN and to optimize therapeutic management.<\/jats:p>","DOI":"10.3389\/fmed.2026.1799421","type":"journal-article","created":{"date-parts":[[2026,7,6]],"date-time":"2026-07-06T11:10:31Z","timestamp":1783336231000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Case Report: Late-onset BK polyomavirus-associated nephropathy in kidney transplant recipients: two cases and insights into underlying mechanisms"],"prefix":"10.3389","volume":"13","author":[{"given":"Tanja","family":"Bel\u010di\u010d Miki\u010d","sequence":"first","affiliation":[{"name":"Department of Nephology, University Medical Center Ljubljana","place":["Ljubljana, Slovenia"]},{"name":"Faculty of Medicine, University of Ljubljana","place":["Ljubljana, Slovenia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Matic","family":"Bo\u0161njak","sequence":"additional","affiliation":[{"name":"Faculty of Medicine, University of Ljubljana","place":["Ljubljana, Slovenia"]},{"name":"Faculty of Medicine, Institute of Pathology, University of Ljubljana","place":["Ljubljana, Slovenia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Miha","family":"Arnol","sequence":"additional","affiliation":[{"name":"Department of Nephology, University Medical Center Ljubljana","place":["Ljubljana, Slovenia"]},{"name":"Faculty of Medicine, University of Ljubljana","place":["Ljubljana, Slovenia"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,7,6]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"286","DOI":"10.2215\/CJN.15971020","article-title":"Long-term infectious complications of kidney transplantation","volume":"17","author":"Agrawal","year":"2022","journal-title":"Clin J Am Soc Nephrol"},{"key":"B2","doi-asserted-by":"publisher","first-page":"12065","DOI":"10.3389\/ti.2024.12065","article-title":"Beyond the first year: epidemiology and management of late-onset opportunistic infections after kidney transplantation","volume":"37","author":"Esnault","year":"2024","journal-title":"Transpl Int."},{"key":"B3","doi-asserted-by":"publisher","first-page":"19","DOI":"10.1007\/0-387-32957-9_2","article-title":"Discovery and epidemiology of the human polyomaviruses BK virus (BKV) and JC virus (JCV)","volume":"577","author":"Knowles","year":"2006","journal-title":"Adv Exp Med Biol."},{"key":"B4","doi-asserted-by":"publisher","first-page":"1253","DOI":"10.1016\/S0140-6736(71)91776-4","article-title":"New human papovavirus (B. 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