Detection of BK polyomavirus after kidney transplantation: a comparison of urine electron microscopy with plasma polymerase chain reaction

Serum and urine nucleic acid screening tests for BK polyomavirus-associated nephropathy in kidney and kidney-pancreas transplant recipients

BACKGROUND

BK polyomavirus-associated nephropathy (BKPyVAN) occurs when BK polyomavirus (BKPyV) affects a transplanted kidney, leading to an initial injury characterised by cytopathic damage, inflammation, and fibrosis. BKPyVAN may cause permanent loss of graft function and premature graft loss. Early detection gives clinicians an opportunity to intervene by timely reduction in immunosuppression to reduce adverse graft outcomes. Quantitative nucleic acid testing (QNAT) for detection of BKPyV DNA in blood and urine is increasingly used as a screening test as diagnosis of BKPyVAN by kidney biopsy is invasive and associated with procedural risks. In this review, we assessed the sensitivity and specificity of QNAT tests in patients with BKPyVAN.

OBJECTIVES

We assessed the diagnostic test accuracy of blood/plasma/serum BKPyV QNAT and urine BKPyV QNAT for the diagnosis of BKPyVAN after transplantation. We also investigated the following sources of heterogeneity: types and quality of studies, era of publication, various thresholds of BKPyV-DNAemia/BKPyV viruria and variability between assays as secondary objectives.

SEARCH METHODS

We searched MEDLINE (OvidSP), EMBASE (OvidSP), and BIOSIS, and requested a search of the Cochrane Register of diagnostic test accuracy studies from inception to 13 June 2023. We also searched ClinicalTrials.com and the WHO International Clinical Trials Registry Platform for ongoing trials.

SELECTION CRITERIA

We included cross-sectional or cohort studies assessing the diagnostic accuracy of two index tests (blood/plasma/serum BKPyV QNAT or urine BKPyV QNAT) for the diagnosis of BKPyVAN, as verified by the reference standard (histopathology). Both retrospective and prospective cohort studies were included. We did not include case reports and case control studies.

DATA COLLECTION AND ANALYSIS

Two authors independently carried out data extraction from each study. We assessed the methodological quality of the included studies by using Quality Assessment of Diagnostic-Accuracy Studies (QUADAS-2) assessment criteria. We used the bivariate random-effects model to obtain summary estimates of sensitivity and specificity for the QNAT test with one positivity threshold. In cases where meta-analyses were not possible due to the small number of studies available, we detailed the descriptive evidence and used a summative approach. We explored possible sources of heterogeneity by adding covariates to meta-regression models.

MAIN RESULTS

We included 31 relevant studies with a total of 6559 participants in this review. Twenty-six studies included kidney transplant recipients, four studies included kidney and kidney-pancreas transplant recipients, and one study included kidney, kidney-pancreas and kidney-liver transplant recipients. Studies were carried out in South Asia and the Asia-Pacific region (12 studies), North America (9 studies), Europe (8 studies), and South America (2 studies).

INDEX TEST

blood/serum/plasma BKPyV QNAT The diagnostic performance of blood BKPyV QNAT using a common viral load threshold of 10,000 copies/mL was reported in 18 studies (3434 participants). Summary estimates at 10,000 copies/mL as a cut-off indicated that the pooled sensitivity was 0.86 (95% confidence interval (CI) 0.78 to 0.93) while the pooled specificity was 0.95 (95% CI 0.91 to 0.97). A limited number of studies were available to analyse the summary estimates for individual viral load thresholds other than 10,000 copies/mL. Indirect comparison of thresholds of the three different cut-off values of 1000 copies/mL (9 studies), 5000 copies/mL (6 studies), and 10,000 copies/mL (18 studies), the higher cut-off value at 10,000 copies/mL corresponded to higher specificity with lower sensitivity. The summary estimates of indirect comparison of thresholds above 10,000 copies/mL were uncertain, primarily due to a limited number of studies with wide CIs contributed to the analysis. Nonetheless, these indirect comparisons should be interpreted cautiously since differences in study design, patient populations, and methodological variations among the included studies can introduce biases. Analysis of all blood BKPyV QNAT studies, including various blood viral load thresholds (30 studies, 5658 participants, 7 thresholds), indicated that test performance remains robust, pooled sensitivity 0.90 (95% CI 0.85 to 0.94) and specificity 0.93 (95% CI 0.91 to 0.95). In the multiple cut-off model, including the various thresholds generating a single curve, the optimal cut-off was around 2000 copies/mL, sensitivity of 0.89 (95% CI 0.66 to 0.97) and specificity of 0.88 (95% CI 0.80 to 0.93). However, as most of the included studies were retrospective, and not all participants underwent the reference standard tests, this may result in a high risk of selection and verification bias.

INDEX TEST

urine BKPyV QNAT There was insufficient data to thoroughly investigate both accuracy and thresholds of urine BKPyV QNAT resulting in an imprecise estimation of its accuracy based on the available evidence.

AUTHORS' CONCLUSIONS

There is insufficient evidence to suggest the use of urine BKPyV QNAT as the primary screening tool for BKPyVAN. The summary estimates of the test sensitivity and specificity of blood/serum/plasma BKPyV QNAT test at a threshold of 10,000 copies/mL for BKPyVAN were 0.86 (95% CI 0.78 to 0.93) and 0.95 (95% CI 0.91 to 0.97), respectively. The multiple cut-off model showed that the optimal cut-off was around 2000 copies/mL, with test sensitivity of 0.89 (95% CI 0.66 to 0.97) and specificity of 0.88 (95% CI 0.80 to 0.93). While 10,000 copies/mL is the most commonly used cut-off, with good test performance characteristics and supports the current recommendations, it is important to interpret the results with caution because of low-certainty evidence.

Polyoma BK Virus in Kidney Transplant Recipients: Screening, Monitoring, and Management

Polyomavirus BK virus (BKPyV) infection is an important complication of kidney transplantation and allograft failure. The prevalence of viremia is 10%-15%, compared with BK-associated nephropathy (BKPyVAN) at 3%-5%. Given that there are no effective antiviral prophylaxis or treatment strategies for BKPyVAN, active screening to detect BKPyV viremia is recommended, particularly during the early posttransplant period. Immunosuppression reduction to allow viral clearance may avoid progression to severe and irreversible allograft damage. The frequency and duration of screening are highly variable between transplant centers because the evidence is reliant largely on observational data. While the primary treatment goals center on achieving viral clearance through immunosuppression reduction, prevention of subsequent acute rejection, premature graft loss, and return to dialysis remain as major challenges. Treatment strategies for BKPyV infection should be individualized to the recipient's underlying immunological risk and severity of the allograft infection. Efficacy data for adjuvant therapies including intravenous immunoglobulin and cidofovir are sparse. Future well-powered and high-quality randomized controlled trials are needed to inform evidence-based clinical practice for the management of BKPy infection.

Prophylactic and therapeutic adenoviral vector-based multivirus-specific T-cell immunotherapy for transplant patients

Viral infections including cytomegalovirus, Epstein-Barr virus, adenovirus, and BK virus are a common and predictable problem in transplant recipients. While cellular immune therapies have been successfully used to tackle infectious complications in transplant recipients, manufacturing immunotherapies to address the multitude of possible pathogens can be technically challenging and labor-intensive. Here we describe a novel adenoviral antigen presentation platform (Ad-MvP) as a tool for rapid generation of multivirus-specific T-cells in a single step. Ad-MvP encodes 32 CD8+ T-cell epitopes from cytomegalovirus, Epstein-Barr virus, adenovirus, and BK virus as a contiguous polyepitope. We demonstrate that Ad-MvP vector can be successfully used for rapid in vitro expansion of multivirus-specific T-cells from transplant recipients and in vivo priming of antiviral T-cell immunity. Most importantly, using an in vivo murine model of Epstein-Barr virus-induced lymphoma, we also show that adoptive immunotherapy with Ad-MvP expanded autologous and allogeneic multivirus-specific T-cells is highly effective in controlling Epstein-Barr virus tumor outgrowth and improving overall survival. We propose that Ad-MvP has wide ranging therapeutic applications in greatly facilitating in vivo priming of antiviral T-cells, the generation of third-party T-cell banks as “off-the-shelf” therapeutics as well as autologous T-cell therapies for transplant patients.

Prevalence of polyoma BK virus infection among living-donor renal transplant recipients

BACKGROUND

Polyomavirus nephropathy (PVN) mainly caused by BK polyomavirus (BKPyV) remains the most common productive viral infection of the kidney in immunosuppressed patients. The diagnosis of PVN is based on the detection of BK viruria and BK viremia in conjunction with histological findings in the graft biopsy.

METHODS

Our study was aimed to estimate the prevalence of productive BKPyV infection among renal transplant patients within the first year post-transplant and identify those at risk of developing PVN. Our cross-sectional study was conducted on 134 kidney transplant patients. Evidence of BKPyV replication was assessed by viral quantification of blood and urine samples of studied patients using a quantitative real-time polymerase chain reaction (Q-PCR)PCR), detection of decoy cells in urine cytology smears, histological examination of graft biopsies from Q-PCR BKPyV-positive patients, and immunohistochemical staining by simian virus 40 (SV40) antibody.

RESULTS

Significant BKPyV infection was prevalent in 8% (n = 11) of our patients, with a peak of BKPyV infection about 8 months post transplant. BKPyV viral load by Q-PCR assay in these patients varied from 1350 to 20,000,000 (1.35 × 10(3) to 2 × 10(7) ) copies/mL for urine samples and 935 to 18,920 (9.35 × 10(2) to 1.89 × 10(4) ) copies/mL for blood samples. All the 11 patients were positive for decoy cells but only 3 developed PVN based on histology and positive SV40 staining. BKPyV infection was more prevalent in older patients. All patients responded to reduction in their immunosuppressive regimens, apart from 2 patients who required replacement of calcineurin inhibitors-based regimen with mammalian target of ramapycin inhibitors with an overall good response.

CONCLUSION

Protocol screening programs based on detection of viral replication by viruria, viremia, and decoy cells in urine are necessary to shed light on patients with high virus replication and hence increased risk of developing PVN, and to allow early diagnosis and intervention.

Difference of two dependent sensitivities and specificities: Comparison of various approaches

In diagnostic studies, a new diagnostic test is often compared with a standard test and both tests are applied on the same patients, called paired design. The true disease state is in general given by the so-called gold standard (most reliable method for classification), which has to be known for all patients. The benefit of the new diagnostic test can be evaluated by sensitivity and specificity, which are in fact proportions. This means, for the comparison of two diagnostic tests, confidence intervals for the difference of the dependent estimated sensitivities and specificities are calculated. In the literature, many comparisons of different approaches can be found, but none explicitly for diagnostic studies. For this reason we compare 13 approaches for a set of scenarios that represent data of diagnostic studies (e.g., with sensitivity and specificity ≥0.8). With simulation studies, we show that the nonparametric interval with normal approximation can be recommended for the difference of two dependent sensitivities or specificities without restriction, the Wald interval with the limitation of slightly anti-conservative results for small sample sizes, and the nonparametric intervals with t-approximation, and the Tango interval with the limitation of conservative results for high correlations.