*Purpose: BK polyomavirus-associated nephropathy (BKVN) after kidney transplantation is associated with a high morbidity and higher risk of graft loss. In this study, the relationship between BKVN post-kidney transplantation and HLA, and between killer immunoglobulin-like receptor (KIR) compatibility of recipients and donors was evaluated.

*Methods: We included 228 cases among patients who received a living kidney transplants at Akita University Hospital from December 2004 to November 2016. BKVN replication was evaluated by detection of decoy cells in urine cytology smears and/or immunohistochemical staining by simian virus 40 positive cells in graft biopsy. Using HLA and KIR haplotypes were determined by WAKFlow and LAB type reagents, HLA loci type and HLA match/HLA-KIR match between donor and recipient were evaluated.

*Results: Eleven cases were diagnosed with BKVN infection after renal transplant (4.8% of the total). In the analysis using HLA loci type, BKVN was significantly high frequency in A24 and DR14 carriers compared with each non-carrier (8.4% vs 0.9%; p=0.011 and 12.8% vs 2.8%; p=0.011, respectively). In the analysis using HLA match, the incidence in the 2- or 1-match case group of HLA-DR14 was significantly higher than in the 0-match case group (19.0% vs. 3.4%, p=0.012) while there were no association of BKVN with other HLA match. In Kaplan-Meier analysis, HLA-A24 carrier, HLA-DR14 carrier and HLA-DR14 match were significantly high morbidity compared with non-carrier/match (p=0.009, p=0.005 and p=0.002, respectively). On the other hand, as a result of comparison among KIR haplotypes and of comparison with or without KIR-ligand match between recipient KIR and donor HLA, there were no significant different of BKVN frequency.

*Conclusions: HLA and match/mismatch in kidney transplantation are important not only for suppressing alloresponse but also for predicting BKVN.

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