Significance, cytomorphology of decoy cells in polyomavirus-associated nephropathy: Review of clinical, histopathological, and virological correlates with commentary

BK polyomavirus: latency, reactivation, diseases and tumorigenesis

The identification of the first human polyomavirus BK (BKV) has been over half century, The previous epidemiological and phylogenetic studies suggest that BKV prevailed and co-evolved with humans, leading to high seroprevalence all over the world. In general, BKV stays latent and symptomless reactivation in healthy individuals. BKV has been mainly interlinked with BKV-associated nephropathy (BKVAN) in kidney-transplant recipients and hemorrhagic cystitis (HC) in hematopoietic stem cell transplant recipients (HSCTRs). However, the mechanisms underlying BKV latency and reactivation are not fully understood and lack of extensive debate. As Merkel cell polyomavirus (MCV) was identified as a pathogenic agent of malignant cutaneous cancer Merkel cell carcinoma (MCC) since 2008, linking BKV to tumorigenesis of urologic tumors raised concerns in the scientific community. In this review, we mainly focus on advances of mechanisms of BKV latency and reactivation, and BKV-associated diseases or tumorigenesis with systematical review of formerly published papers following the PRISMA guidelines. The potential tumorigenesis of BKV in two major types of cancers, head and neck cancer and urologic cancer, was systematically updated and discussed in depth. Besides, BKV may also play an infectious role contributing to HIV-associated salivary gland disease (HIVSGD) presentation. As more evidence indicates the key role of BKV in potential tumorigenesis, it is important to pay more attention on its etiology and pathogenicity in vitro and in vivo.

Presence of decoy cells for 6 months on urine cytology efficiently predicts BK virus nephropathy in renal transplant recipients

OBJECTIVES

To investigate the association between duration of consecutive presence of decoy cells on urine cytology and BK virus nephropathy after kidney transplantation.

METHODS

In total, 121 kidney transplant recipients were retrospectively evaluated. The best duration of consecutive presence of decoy cells that could be used to predict BK virus nephropathy was analyzed using the area under the curve for each duration, and recipients were divided into two groups based on the best predictive performance. The effectiveness of SV40 immunostaining on urinary cytology was also analyzed.

RESULTS

In total, 2534 urine specimens as well as SV40 immunostaining in 2241 urine specimens were analyzed. Six consecutive months of decoy cell positivity had the best predictive performance for BK virus nephropathy (area under the curve = 0.832). The incidence of BK virus nephropathy in recipients with positive decoy cells for 6 months or more consecutive months (5/44) was significantly higher than in those who had positive decoy cells for less than 6 months (0/77; P = 0.005). Decoy cell positivity had a sensitivity, specificity, positive predictive value, and negative predictive value for BK virus nephropathy of 100%, 66%, 11%, and 100% respectively. SV40 immunostaining provided slightly better specificity (68%) and positive predictive value (12%).

CONCLUSIONS

The detection of decoy cells at 6 months or more on urine cytology had high predictive value for BK virus nephropathy in kidney transplant recipients. SV40 immunostaining on urine cytology added minimal diagnostic accuracy.