Monitoring of Polyomavirus BK Virus Viruria and Viremia in Renal Allograft Recipients by Use of a Quantitative Real-Time PCR Assay: One-Year Prospective Study

Abstract

We have developed a real-time quantitative PCR (rt-QPCR) assay to detect and kinetically monitor BK virus viruria and viremia in renal transplant recipients (RTRs). A total of 607 urine and 223 plasma samples were collected from 203 individuals including those with BK virus-associated nephropathy (BKVAN) (n ‫؍‬ 8), those undergoing routine posttransplant surveillance (SV) (n ‫؍‬ 155), those with nontransplant chronic kidney disease (NT-CKD) (n ‫؍‬ 20), and healthy living kidney donors (LD) (n ‫؍‬ 20). The rt-QPCR assay was found to be highly sensitive and specific, with a wide dynamic range (2.4 to 11 log 10 copies/ml) and very good precision (coefficient of variation, ϳ5.9%). There was a significant difference in the prevalences of viruria and viremia between the BKVAN (100% and 100%) and SV (23% and 3.9%) groups (P < 0.001). No viruria or viremia was detected in LD or in NT-CKD patients. The median (range) peak levels of BK virus viruria and viremia, in log 10 copies/ml, were 10.26 (9.04 to 10.83) and 4.83 (3.65 to 5.86) for the BKVAN group versus 0 (0 to 10.83) and 0 (0 to 5.65) for the SV group, respectively (P < 0.001). When the BK virus load in the urine was <7.0 log 10 copies/ml, no BK virus viremia was detected. When the BK virus load in the urine reached 7.0, 8.0, 9.0, and >10.0 log 10 copies/ml, the corresponding detection of BK virus viremia increased to 20, 33, 50, and 100%, respectively. We propose monitoring of BK virus viruria in RTRs, with plasma BK virus load testing reserved for those with viruria levels of >7.0 log 10 copies/ml. BK virus (BKV) is a polyomavirus with a circular DNA genome of approximately 5,300 bp. BKV causes ubiquitous infection in early childhood, with seroprevalence in adults ranging from 60 to 100% (31). Following primary infection, the virus remains latent in the urogenital tract (30). BKV reactivation with urinary shedding of infected urothelial cells occurs in 10 to 60% of renal transplant recipients (RTR) (19,25). Although early studies found that only sporadic cases of graft dysfunction were associated with viral activation (1, 14, 15), more-recent studies demonstrate BKV-associated nephropathy (BKVAN) in as many as 8% of renal allograft recipients, with as many as 50% of patients experiencing graft loss over the next 2 to 3 years of follow-up (8, 9, 11, 20-24, 27, 28, 29). Accumulated data suggest that prospective monitoring of patients at risk for BKVAN may identify those with active infection before renal function deteriorates (3,8,13,18,22). Early identification provides the opportunity for intervention with reduction of the immunosuppression in an effort to control BKV replication and prevent BKVAN (4, 16).Progression to BKVAN occurs without clinical signs or symptoms except for increasing serum creatinine concentrations. The "gold standard" for diagnosis of BKVAN continues to be renal biopsy with demonstration of viral cytopathic tubulointerstitial changes (7, 23). Sometimes, however, the biopsy result can be falsely negative due to the focal nature of the diseas...

Toward Standardization of BK Virus Monitoring: Evaluation of the BK Virus R-gene Kit for Quantification of BK Viral Load in Urine, Whole-Blood, and Plasma Specimens

“…Monitoring of BKV viruria is noninvasive and can be informative, as a high level of BK viruria usually precedes viremia and potential nephropathy by 4 to 12 weeks (1,27). Even though a cutoff value or a positive predictive value is hard to define, a viruria level of Ͼ7 log 10 should alert clinicians and indicate the need to increase surveillance of viremia (28). Regarding the assessment of BKVL in the blood compartment, validation of WB as an appropriate matrix was recently carried out (29), but no study thus far has endeavored to contrast plasma and WB samples for BKVL determination.…”

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“…24 The high level of creatinine in kidney allograft recipients, reported from different regions, is the first indication of suspicious involvement of this viral infection in nephropathy, which calls for measuring viral loads in urine and plasma of such patients. 9,25,26 The natural history of BK polyomavirus infection and reactivation in kidney transplant patients is poorly understood. However, some evidence indicates that transplant patients with BKVAN had frequent rearrangements in the NCCR genomic region of BK polyomavirus isolated from either circulatory specimens including blood, serum, and plasma or from their urogenital region such as kidney biopsy specimens and urine.…”

“…Recent studies showed that BK polyomavirus is associated with nephropathy in 8% kidney allograft recipients. [7][8][9] Different studies suggest that prospective monitoring of patients who are at risk for BKVAN may help to identify active infection in those who may have borderline deteriorated kidney function. 7,9,10 Control of BK polyomavirus replication and prevention of BKVAN is possible by tapering the dose of immunosuppressive drugs.…”

“…[7][8][9] Different studies suggest that prospective monitoring of patients who are at risk for BKVAN may help to identify active infection in those who may have borderline deteriorated kidney function. 7,9,10 Control of BK polyomavirus replication and prevention of BKVAN is possible by tapering the dose of immunosuppressive drugs. 9,11 Adaptation of BK polyomavirus with infected host cells may lead to rearrangement of the viral genomic region known as noncoding control region (NCCR) or noncoding regulatory region (NCRR).…”

“…7,9,10 Control of BK polyomavirus replication and prevention of BKVAN is possible by tapering the dose of immunosuppressive drugs. 9,11 Adaptation of BK polyomavirus with infected host cells may lead to rearrangement of the viral genomic region known as noncoding control region (NCCR) or noncoding regulatory region (NCRR). 12 The genome of BK polyomavirus consists of the genetically conserved coding region and the hypervariable NCCR (300-500 bp).…”