BK Viremia and Changes in Estimated Glomerular Filtration Rate in Children and Young Adults after Hematopoietic Cell Transplantation

Kidney disease in allogeneic hematopoietic cell transplantation (HCT) recipients is associated with increased mortality rates. BK virus (BKV) viremia has been associated with kidney dysfunction in pediatric HCT recipients; however, few studies have investigated longer-term kidney outcomes in association with BKV in this population. Here we assessed the relationship between BK viremia and changes in estimated glomerular filtration rate (eGFR) in children in the first year post-HCT. We selected 136 patients age ≤26 years who underwent HCT in 2007 to 2018 at a single center and had plasma BK viral load data available at 2 time points, weeks 4 to 7 post-HCT and weeks 10 to 13 post-HCT from prospectively collected stored plasma samples. A total of 272 samples were analyzed for BKV using quantitative PCR. We used multivariate linear models to determine the association of BK viremia and change in eGFR by 1 year post-HCT. Forty percent of the patients (54 of 136) had BKV detection in weeks 4 to 7, 13% of whom (7 of 54) had a BK viral load of ≥10,000 copies/mL, and 46% (62 of 136) had BKV detected in weeks 10 to 13, 34% (21 of 62) of whom had a BK viral load of ≥10,000 copies/mL. The mean decline in eGFR was 25.73 mL/min/1.73 m² by 1 year post-HCT. In multivariate models, a BK viral load of ≥10,000 copies/mL during weeks 4 to 7 was associated with a mean decline in eGFR of 30.6 mL/min/1.73 m² (95% confidence interval, -55.94 to -5.17; P = .019) compared with a BK viral load <10,000 copies/mL. In adjusted analyses, a high BK viral load in the blood (≥10,000 copies/mL) was associated with a significant decline in eGFR by 1 year post-HCT.

BK virus nephropathy in non-renal solid organ transplant recipients: Are we looking hard enough?

We retrospectively examined the clinical characteristics, pathological features, and outcomes of BK viremia and nephropathy in a population of non-renal solid organ transplant patients (NRSOT) referred for outpatient nephrology consultation over a period of 5 years. In the entire cohort of liver, heart, and lung transplant recipients referred to this clinic, 14% percent were found to have BK viremia with a median peak serum BK viral load of 35 500 copies/ml (range 250 to 21 100 000 copies/ml). BK viremia resolved in six of the seventeen patients (35%). Four out of five patients biopsied showed BK virus (BKV) nephropathy. Eleven out of seventeen patients with BK viremia developed advanced (stage 4 or 5) chronic kidney disease. Four patients developed rejection of their solid organ transplant within the first year post detection of BK viremia after immunosuppression reduction. We conclude that a multi-center study is required to evaluate whether implementation of a systematic BK screening program would be effective in early detection and management of this problem in the NRSOT population.

BK virus nephropathy in a heart transplant recipient

BK virus nephropathy in kidney transplantation is widely recognized as an important cause of graft dysfunction and loss. In the case of transplants of organs other than kidney, BK virus nephropathy in native kidneys has been recognized as a cause of chronic kidney disease, which is related with immunosuppression; however, the diagnosis is usually late because the renal dysfunction is attributed to other causes, such as toxicity by anticalcineurinic drugs, interstitial nephritis due to medications, hemodynamic changes, diabetes, hypertension, etc. We report a case of BK virus nephropathy in a patient who underwent heart transplantation due to peripartum cardiomyopathy. The kidney biopsy reported active chronic tubulointerstitial nephritis associated with late stage polyomavirus nephritis and the blood viral load for BK virus was positive (logarithm 4.5). The immunosuppressive treatment was reduced, and after two years of follow-up, the patient had stable renal function with a serum creatinine of 2.5 mg/dL (GFR of 23.4 mL/min/1.73m2). We recommend that the BK virus be considered as a cause of renal dysfunction in heart transplant recipients, with the aim of detecting its replication in time to reduce immunosuppressive therapy before irreversible compromise of renal function may manifest.

Renal Allograft Biopsies with Polyomavirus BK Nephropathy: Turin Transplant Center, 2015-19

Background: In kidney transplant patients, polyomavirus-associated nephropathy (PVAN) represents a serious complication; the key factor for the development of PVAN is immunosuppression level and modulation of anti-rejection treatment represents the first line of intervention. Allograft biopsy and histology remain the criterion standard for diagnosing PVAN. Methods: All consecutive renal biopsies with the diagnosis of PVAN carried out at the University Hospital City of Health and Science of Turin over a five-years period were studied. Renal allograft biopsy was performed due to renal function alterations associated to medium-high polyomavirus BK (BKV)-DNA levels on plasma specimen. Results: A total of 21 patients underwent a first biopsy to diagnose a possible BKV nephropathy, in 18, a second biopsy was made, in eight, a third biopsy, and finally, three underwent the fourth renal biopsy; following the results of each biopsies, immunosuppressant agents dosages were modified in order to reduce the effect of PVAN. Conclusions: In this study, the clinical and histological features of 21 kidney transplant recipients with BKV reactivation and development of PVAN are described. To date, the only treatment for PVAN consists in the reduction of immunosuppressive agents, constantly monitoring viral load.

BK polyoma virus nephropathy in hematopoietic cell transplant recipients

Background:

The epidemiology of BK polyoma virus nephropathy in hematopoietic cell transplant recipients is poorly characterized. Kidney dysfunction after hematopoietic cell transplant is often attributed to treatment toxicities and kidney biopsies are rarely performed.

Methods:

We reviewed pathology-confirmed BK polyoma virus nephropathy cases in adult and pediatric patients who had undergone a hematopoietic cell transplant between 1 January 2015 and 31 December 2017 at our institution. Plasma and urine BK polyoma virus was assessed by a quantitative polymerase chain reaction assay and were obtained at the clinician discretion. Glomerular filtration rate was estimated by the Chronic Kidney Disease Epidemiology Collaboration equation. BK polyoma virus nephropathy was scored by the Banff Working Group Proposal.

Results:

Eight (7 adult and 1 pediatric) cases of BK polyoma virus nephropathy were identified among 685 hematopoietic cell transplant recipients, 14 of whom had undergone a kidney biopsy. Five patients (62.5%) had received a CD34+-selected peripheral blood hematopoietic cell transplant; two had received a cord blood allograft and one an unmodified peripheral blood hematopoietic cell transplant. Two patients developed acute graft-versus-host disease grade II. Early post–hematopoietic cell transplant BK polyoma viruria was documented with onset at a median of 54 days (range, 6–91) post–hematopoietic cell transplant and median urine BK polyoma viral load was 9.6 log10 copies/mL (range, 8.6–10.0). BK polyoma virus nephropathy was diagnosed at a median of 267 days after hematopoietic cell transplant (range, 133–637). At BK polyoma virus nephropathy diagnosis, all patients had decreased renal function with glomerular filtration rate (median 29 mL/min/1.73 m2; range, 9–98 ) and creatinine (median 2.4 mg/dL; range, 0.8–7.5) ; median plasma BK polyoma viral load was 6.3 log10 copies/mL (range, 5.5–7.1) and median CD4+ lymphocyte count was 82 cell/mcL (range, 21–172).

Conclusions:

We report eight biopsy-proven BK polyoma virus nephropathies in hematopoietic cell transplant recipients from a single center. BK polyoma virus nephropathy should be considered in hematopoietic cell transplant recipients with worsening kidney function and high BK polyoma viremia.

Symptomatic BK virus cystitis in non-renal transplant recipients

BACKGROUND

BK virus is implicated most commonly in causing BK virus-associated nephropathy in renal transplant recipients. However, on rare occasions, it can also produce symptomatic cystitis in other solid organ transplant recipients.

METHODS

Retrospective review of 2,149 non-renal solid organ transplant recipients over a 6-year period to evaluate patients for cases of symptomatic BK virus cystitis.

RESULTS

Three patients (two heart transplant recipients and one lung transplant recipient) are reported herein with symptomatic BK virus cystitis. These patients responded to reduced immunosuppressive medication with a reduction in viral load in two instances, and the third patient appeared to have an apparent response to prolonged levofloxacin treatment.

CONCLUSIONS

A high index of suspicion should be exercised in non-renal solid organ transplant recipients (particularly heart and lung transplant recipients) who have symptoms consistent with cystitis but have a negative urine bacterial culture.

Native kidney BK virus nephropathy, a systematic review

BACKGROUND

There is a growing base of literature describing BK nephropathy (BKVN) in patients outside of the setting of kidney transplant. Previous systematic reviews of the literature have been limited by methodology or by the scope of patients included.

STUDY DESIGN AND METHODS

Systematic Review (Prospero # CRD42018088524).

SETTING & POPULATION

Patients without kidney transplant who had biopsy-proven BKVN.

SELECTION CRITERIA FOR STUDIES

Full-text articles that describe native BKVN patient cases.

ANALYTICAL APPROACH

Descriptive synthesis.

RESULTS

The search identified 630 unique articles of which 51 were included in the final review. Sixty-five cases (including two new cases presented in this review) were identified, all but one occurred in the setting of known immunosuppression.

LIMITATIONS

The primary limitation was the exclusion of studies that did not fulfill the stringent review criteria. We excluded reports with only a clinical diagnosis of BKVN, such as those with viruria and/or viremia without biopsy.

CONCLUSIONS

As of May 2018, there are 65 reported cases of BKVN in native kidneys. This represents the most comprehensive description of biopsy-proven BKVN in native kidneys to date. Evaluation for BK nephropathy should be considered in immunocompromised patients who exhibit unexplained renal failure.

BK polyomavirus in solid organ transplantation-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

The present AST-IDCOP guidelines update information on BK polyomavirus (BKPyV) infection, replication, and disease, which impact kidney transplantation (KT), but rarely non-kidney solid organ transplantation (SOT). As pretransplant risk factors in KT donors and recipients presently do not translate into clinically validated measures regarding organ allocation, antiviral prophylaxis, or screening, all KT recipients should be screened for BKPyV-DNAemia monthly until month 9, and then every 3 months until 2 years posttransplant. Extended screening after 2 years may be considered in pediatric KT. Stepwise immunosuppression reduction is recommended for KT patients with plasma BKPyV-DNAemia of >1000 copies/mL sustained for 3 weeks or increasing to >10 000 copies/mL reflecting probable and presumptive BKPyV-associated nephropathy, respectively. Reducing immunosuppression is also the primary intervention for biopsy-proven BKPyV-associated nephropathy. Hence, allograft biopsy is not required for treating BKPyV-DNAemic patients with baseline renal function. Despite virological rationales, proper randomized clinical trials are lacking to generally recommend treatment by switching from tacrolimus to cyclosporine-A, from mycophenolate to mTOR inhibitors or leflunomide or by the adjunct use of intravenous immunoglobulins, leflunomide, or cidofovir. Fluoroquinolones are not recommended for prophylaxis or therapy. Retransplantation after allograft loss due to BKPyV nephropathy can be successful if BKPyV-DNAemia is definitively cleared, independent of failed allograft nephrectomy.

Effect of polyoma viremia on 3-year allograft kidney function

BACKGROUND

Polyoma viremia is associated with damage to renal tubular and urothelial cells. This may imply that a certain level of viremia, even cleared thereafter, could be associated with long-term renal dysfunction.

METHODS

We, retrospectively, analyzed 390 first renal transplants adult recipients (≥18 years) who were monitored for BK viremia in the first 12 months and evaluated estimated GFR (MDRD-4 equation) at 1 month and at the last follow-up (959 ± 392 days).

RESULTS

One hundred and ninety-nine patients (51%) developed at least one positive viremia: 105 (53%) low viremia (<10⁴  copies/mL), 36 (18%) high viremia (4 × 10⁴  > viremia ≥ 10⁴  copies/mL) and 58 (15%) viremia (≥4 × 10⁴  copies/mL) consistent with polyoma virus associated nephropathy (PyVAN). Out of these 58 patients, 24 (6%) developed bx-proven (SV40+) PyVAN and 34(8.7%) presumptive PyVAN (SV40-). Baseline characteristics, immunosuppression, KDRI, rejection episodes, etc., did not differ among groups but there were more deceased donors and ATG induction therapy in the high viremia group. At last follow-up, all patients in the low, high viremia and presumptive PyVAN (except 2) had cleared BK viremia. Bx-proven PyVAN led to 14 graft losses, 10 due to PyVAN. In the presumptive PyVAN there was only one graft loss registered as due to PyVAN. eGFR, at 1 month after KTx, did not differ among groups (51 ± 22 vs 48 ± 24 vs 45 ± 27 vs 43 ± 18 vs 46 ± 22 mL/min/1.73 m² ), for no, low and high viremia as well for presumptive PyVAN and bx-proven PyVAN groups, respectively. At the last follow-up, eGFR did not differ between the no, low, and high viremia compared to baseline and to each other but was statistically lower in the presumptive and bx-proven PyVAN (38 ± 15 and 17 ± 7 mL/min/1.73 m² ) either compared to baseline or to the other groups.

CONCLUSIONS

This study shows that low and high levels of BK viremia do not lead to GFR changes although very high viremia levels, compatible with presumptive or bx-proven PyVAN, even if cleared thereafter, lead to allograft damage and decreased GFR.

Infections in Heart, Lung, and Heart-Lung Transplantation

Half a century has passed since the first orthotopic heart transplant took place. Surgical innovations allowed for heart, lung, and heart-lung transplantation to save lives of patients with incurable chronic cardiopulmonary conditions. The complexity of the surgical interventions, chronic host health conditions, and antirejection immunosuppressive medications makes infectious complications common. Infections have remained one of the main barriers for successful transplantation and a source of significant morbidity and mortality. Recognition of infections and its management in this setting require outstanding clinical skills since transplant recipients may not exhibit classic signs or symptoms of disease, and laboratory work has some pitfalls. The prevention, identification, and management of infectious diseases complications in this population are a priority to undertake to improve the medical outcomes of transplantation. Herein, we reviewed the historical aspects, epidemiology, and prophylaxis of infections in heart, lung, and heart-lung transplantation. We also discuss the most prevalent organisms affecting the host and the organ systems involved.

The impact of recipient BKV shedding before transplant on BKV viruria, DNAemia, and nephropathy post-transplant: A prospective study

We previously demonstrated that detectable BKV replication in donor urine pretransplant was significantly associated with post-transplant recipient BKV viremia. In this 4-year prospective study, we assessed whether recipient BKV replication pretransplant was associated with post-transplant viremia/BKV nephropathy. We studied 220 primary adult and pediatric organ transplant recipients for 490 person-years and 2100 clinical visits. BKV viruria was detectable in 28 (16%), 26 adults and two children; and viremia in none pretransplant. Post-transplant viruria occurred in all recipients with pretransplant BKV viruria, significantly more than in recipients without pretransplant viruria on univariate (P<.005) and multivariate analysis including type of organ transplanted and immunosuppression type (P .008). Time to post-transplant viruria was significantly shorter in recipients with pretransplant viruria (P .01). By univariate and multivariate analysis, BKV viruria in recipients pretransplant did not impact post-transplant BKV viremia (P=.97 and .97, respectively) even when stratified by type of organ transplant (kidney P=.6; liver P=.5). The peak serum and urine BKV PCR post-transplant were not significantly different in patients with pretransplant BKV viruria and no one developed BK nephropathy. In conclusion, recipient BKV viruria prior to transplant predicts post-transplant viruria but not viremia or BKV nephropathy.

European perspective on human polyomavirus infection, replication and disease in solid organ transplantation

Human polyomaviruses (HPyVs) are a growing challenge in immunocompromised patients in view of the increasing number of now 12 HPyV species and their diverse disease potential. Currently, histological evidence of disease is available for BKPyV causing nephropathy and haemorrhagic cystitis, JCPyV causing progressive multifocal leukoencephalopathy and occasionally nephropathy, MCPyV causing Merkel cell carcinoma and TSPyV causing trichodysplasia spinulosa, the last two being proliferative skin diseases. Here, the current role of HPyV in solid organ transplantation (SOT) was reviewed and recommendations regarding screening, monitoring and intervention were made. Pre-transplant screening of SOT donor or recipient for serostatus or active replication is currently not recommended for any HPyV. Post-transplant, however, regular clinical search for skin lesions, including those associated with MCPyV or TSPyV, is recommended in all SOT recipients. Also, regular screening for BKPyV replication (e.g. by plasma viral load) is recommended in kidney transplant recipients. For SOT patients with probable or proven HPyV disease, reducing immunosuppression should be considered to permit regaining of immune control. Antivirals would be desirable for treating proven HPyV disease, but are solely considered as adjunct local treatment of trichodysplasia spinulosa, whereas surgical resection and chemotherapy are key in Merkel cell carcinoma. Overall, the quality of the clinical evidence and the strength of most recommendations are presently limited, but are expected to improve in the coming years.

Late-Onset BK Viruria in Renal Transplant Recipients

BACKGROUND

Most cases of BK virus (BKV) infections emerge within the 1st years of kidney transplantation. We aimed to determine the prevalence of late-onset BKV infection and whether there are any differences between risk factors in early and late BKV infections.

METHODS

In this single-center retrospective study, we reviewed 300 kidney transplant recipients that were under regular follow-up and selected recipients with BKV infection and recorded associated risk factors, connection with immunosuppression, and responses to modification of treatment.

RESULTS

BKV was detected within the 1st 5 years after transplantation in 20 patients (6.6%, group 1) and after 5 years in 15 patients (5.0%, group 2). There were no significant differences between the 2 groups regarding age, sex, sex mismatches, donor type, BKV elimination time, serum creatinine, and estimated glomerular filtration rate at the times of BKV detection and last follow-up visit. In group 1, 2 recipients had biopsy-proven BKV-associated nephropathy (BKVAN), 3 recipients had BK viruria and viremia without BKVAN (biopsy proven), and 15 recipients (75%) had only BK viruria. In group 2, all of the patients had only BK viruria. In this group, on detection of BK viruria and immediate modification of immunosuppressive regimens prevented BK viremia.

CONCLUSIONS

Routine screening of renal transplant recipients for BKV was indicated not only during the 1st 5 years, but also for the full follow-up period after transplantation.

Review article: BK virus in systemic lupus erythematosus

BK virus (BKV) is a human polyomavirus with a seroprevalence of 60-80 % in the general population. In renal transplant patients, it is known to cause renal failure, ureteric stenosis and hemorrhagic cystitis. In bone marrow transplant patients, it is evident that BKV can also cause hemorrhagic cystitis along with BK virus nephropathy (BKVN) in the native kidneys, with subsequent renal failure. However, little is known about BVKN in non-transplanted immune-compromised patients, such as systemic lupus erythematosus (SLE) who may have underlying nephritis and have a compromised immune system due to therapy and/or systemic illness. Thus, this article will focus on the clinical aspects of BKV and its association in patients with SLE.

Polyomaviruses and disease: is there more to know than viremia and viruria?

Purpose of review

Polyomavirus nephropathy (PVN) mainly caused by BK virus (BKV) remains the most common productive viral infection of the kidney. Over the past decade, clinical interest often focused on BK viremia and viruria as the diagnostic mainstays of patient management. The purpose of this review is to discuss viral nephropathy in the context of BK viremia and viruria and new strategies to optimize diagnostic accuracy and patient management. The emerging roles of polyomaviruses in oncogenesis, salivary gland disease, and post-bone marrow transplantation as well as novel Polyomavirus strains are highlighted.

Recent findings

Areas of investigation include proposals by the Banff working group on the classification of PVN and studies on PVN progression and resolution, including the role cellular immune responses may play during reconstitution injury. New noninvasive strategies to optimize the diagnosis of PVN, that is, the urinary ‘polyomavirus-haufen’ test and mRNA expression levels for BKV in the urine, hold great promise to accurately identify patients with viral nephropathy. Tools are now available to separate ‘presumptive’ from ‘definitive’ disease in various patient cohorts including individuals post-bone marrow transplantation. Recent observations also point to a currently underrecognized role of polyomaviruses in oncogenesis post-transplantation and salivary gland disease in patients with HIV-AIDS.

Summary

This review summarizes recent studies on PVN and the significance of the BKV strain in disease. Current paradigms for patient management post-(renal) transplantation are discussed in the setting of new observations. Issues that still require clarification and further validation are highlighted.

A Case of BK Nephropathy without Detectable Viremia or Viruria

Patient: Male, 49

Final Diagnosis: BK nephropathy without detectable viremia or viruria

Symptoms: —

Medication: —

Clinical Procedure: Kidney biopsy

Specialty: Nephrology

Different risk factor profiles distinguish early-onset from late-onset BKV-replication

Two of three reactivations of latent BKV-infection occur within the first 6 months after renal transplantation. However, a clear differentiation between early-onset and late-onset BKV-replication is lacking. Here, we studied all kidney transplant recipients (KTRs) at our single transplant center between 2004 and 2012. A total of 103 of 862 KTRs were diagnosed with BK viremia (11.9%), among which 24 KTRs (2.8%) showed progression to BKV-associated nephropathy (BKVN). Sixty-seven KTRs with early-onset BKV-replication (65%) and 36 KTRs with late-onset BKV-replication (35%) were identified. A control group of 598 KTRs without BKV-replication was used for comparison. Lymphocyte-depleting induction, CMV-reactivation, and acute rejection increased the risk of early-onset BKV-replication (P < 0.05). Presensitized KTRs undergoing renal retransplantation were those at increased risk of late-onset BKV-replication (P < 0.05). Among KTRs with BK viremia, higher doses of mycophenolate increased the risk of progression to BKVN (P = 0.004). KTRs with progression to BKVN showed inferior allograft function (P < 0.05). KTRs with late-onset BK viremia were more likely not to recover to baseline creatinine after BKV-replication (P = 0.018). Our data suggest different risk factors in the pathogenesis of early-onset and late-onset BKV-reactivation. While a more intensified immunosuppression is associated with early-onset BKV-replication, a chronic inflammatory state in presensitized KTRs may contribute to late-onset BKV-replication.

BK Virus Nephropathy in Heart Transplant Recipients

Polyomavirus-associated nephropathy (PVAN) has become an important cause of kidney failure in kidney transplant recipients. PVAN is reported to affect 1% to 7% of kidney transplant recipients, leading to premature transplant loss in approximately 30% to 50% of diagnosed cases. PVAN occurring in the native kidneys of solid-organ transplant recipients other than kidney only recently has been noted. We report 2 cases of PVAN in heart transplant recipients, which brings the total of reported cases to 7. We briefly review the literature on the hypothesized causes of PVAN in kidney transplant recipients and comment on whether these same mechanisms also may cause PVAN in other solid-organ transplant recipients. PVAN should be considered in the differential diagnosis when evaluating worsening kidney function. BK viremia surveillance studies of nonkidney solid-organ recipients should be conducted to provide data to assist the transplantation community in deciding whether regular monitoring of nonkidney transplant recipients for BK viremia is indicated.

Brincidofovir for polyomavirus-associated nephropathy after allogeneic hematopoietic stem cell transplantation

Polyomavirus-associated nephropathy (PVAN) is common in patients who have undergone kidney transplantation and has been reported in hematopoietic stem cell (HSC) transplant recipients. Aside from reduction of immunosuppression, few therapeutic options exist for treatment of PVAN. We report a case of PVAN in a severely immunocompromised allogeneic HSC transplant recipient that was treated with brincidofovir without reduction of immunosuppression. We review our institutional experience of PVAN in HSC transplantation and discuss the potential use of brincidofovir for treatment.

The kinetics of urinary shedding of BK virus in children with renal disease

Children with renal diseases are typically treated with immunosuppressive drugs, which place them at high risk of reactivation of the BK virus (BKV). Currently, little is known about the impact of immunosuppressive drugs on the kinetics of urinary shedding of BKV and viral reactivation in pediatric patients with renal diseases. Urine samples were collected monthly for 1 year from 20 children (median age, 9 years; range, 4-15 years) with renal diseases and subjected to real-time PCR. Urinary shedding of BKV was detected in 35% (7/20) of the patients, three of these patients having persistent viral DNA excretion (two cases, twelve times; one case, four times) and four having intermittent viral DNA excretion. Thirty-four of the 240 urine samples contained BKV DNA (median copy numbers, 5.66 log copies/mL; range, 2.45-7.69 log copies/mL). In two of the cases with persistent viral shedding, high copy numbers (range, 4.57-7.69 log copies/mL) of BKV DNA were detected in all 12 urine samples collected. In the other case with persistent viral excretion, a range of 2.45-3.98 log copies/mL of BKV DNA was detected in the four urine samples collected between the 9th and 12th sampling time points. Additionally, high copy numbers (range, 3.12-4.36 log copies/mL) of BKV DNA were detected intermittently in the urine samples of the other four cases. No remarkable correlations were found between the kinetics of BKV DNA loads and urinary findings such as proteinuria and hematuria. The present data demonstrate the kinetics of urinary BKV shedding in pediatric patients with renal diseases. Additionally, no pathogenic role for BKV infection was identified.

Renal pathology associated with hematopoietic stem cell transplantation

The kidney is subject to a large variety of injurious factors before, during, and after hematopoietic stem cell transplantation (HCT), leading to a high incidence of acute kidney injury in the peritransplant period. Chronic kidney disease is estimated to impact 15% to 20% of HCT recipients. Although renal biopsies may be deferred in the setting of thrombotic microangiopathy, acute self-limited impairment, or slowly progressive functional decline, in many patients renal biopsy yields important diagnostic insight to guide treatment. Light microscopic, immunofluorescence, and ultrastructural analysis often reveals a number of concurrent abnormalities in glomeruli, tubules, interstitium, and vessels. Meta-analysis of the literature reveals that membranous nephropathy is the most commonly reported glomerular lesion in the setting of HCT, followed by minimal change disease. Autopsy and biopsy studies show that clinical criteria lack sensitivity and specificity for renal acute and chronic thrombotic microangiopathy. Viral infection and other causes of interstitial nephritis and tubular injury are important findings in HCT renal biopsies, which in many instances may not be clinically suspected. Given the complexity and variability of HCT protocols, clinicopathologic correlation is needed.

BK Virus and Its Role in Hematopoietic Stem Cell Transplantation: Evolution of a Pathogen

We reviewed the literature regarding disease induced by BK virus (BKV) in the hematopoietic stem cell transplant (HSCT) population, particularly hemorrhagic cystitis (HC) and nephritis. The association between BKV and HC has been reported over the past four decades. BKV has been clinically implicated and widely accepted as an etiologic agent of HC and nephritis in HSCT and nephropathy in renal transplant patients. We discuss the potential benefit of early initiation of therapy in patients who fail supportive care alone as well as the different treatment strategies for HC induced by BKV. Treatments that have been used such as cidofovir and leflunomide are accompanied by risks, and the benefits are not as concrete as with other viral illness in the HSCT population.

The polyomavirus puzzle: is host immune response beneficial in controlling BK virus after adult hematopoietic cell transplantion?

BK virus (BKV), a ubiquitous human polyomavirus, usually does not cause disease in healthy individuals. BKV reactivation and disease can occur in immunosuppressed individuals, such as those who have undergone renal transplantation or hematopoietic cell transplantation (HCT). Clinical manifestations of BKV disease include graft dysfunction and failure in renal transplant recipients; HCT recipients frequently experience hematuria, cystitis, hemorrhagic cystitis (HC), and renal dysfunction. Studies of HCT patients have identified several risk factors for the development of BKV disease including myeloablative conditioning, acute graft-versus-host disease, and undergoing an umbilical cord blood (uCB) HCT. Although these risk factors indicate that alterations in the immune system are necessary for BKV pathogenesis in HCT patients, few studies have examined the interactions between host immune responses and viral reactivation in BKV disease. Specifically, having BKV immunoglobulin-G before HCT does not protect against BKV infection and disease after HCT. A limited number of studies have demonstrated BKV-specific cytotoxic T cells in healthy adults as well as in post-HCT patients who had experienced HC. New areas of research are required for a better understanding of this emerging infectious disease post HCT, including prospective studies examining BK viruria, viremia, and their relationship with clinical disease, a detailed analysis of urothelial histopathology, and laboratory evaluation of systemic and local cellular and humoral immune responses to BKV in patients receiving HCT from different sources, including uCB and haploidentical donors.

BK virus disease after allogeneic stem cell transplantation: a cohort analysis

The clinical epidemiology of BK virus (BKV) disease after allogeneic hematopoietic stem cell transplantation (HSCT) is not well defined. We evaluated 491 patients transplanted from January 2010 to December 2011 at a single transplant center to assess incidence, severity, and risk factors for BKV disease after HSCT. BKV disease was defined as BKV detection in urine by PCR testing in association with genitourinary symptoms without other concurrent genitourinary conditions. BKV disease occurred in 78 patients (15.9%), for an incidence rate of .47/1000 patient-days (95% confidence interval [CI], .37 to .59); BKV disease was considered severe in 27 patients (5.5%). In multivariate Cox modeling, time-dependent acute graft-versus-host disease (aGVHD) grades II to IV (adjusted hazard ratio [aHR] 4.25; 95% CI, 2.51 to 7.21), cord blood HSCT (aHR 2.28; 95% CI, 1.01 to 5.15), post-transplant mycophenolate use (aHR 3.31; 95% CI, 1.83 to 5.99), and high-dose cyclophosphamide conditioning (aHR 2.34, 95% CI 1.45 to 3.77) were significant predictors of BKV disease. Time-dependent aGVHD grades III to IV (aHR 10.5; 95% CI, 4.44 to 25.0) and cord blood HSCT (aHR 5.40; 95% CI, 1.94 to 15.0) were independent risk factors for severe BKV disease. BKV disease is common and is associated with significant and prolonged morbidity after HSCT. Prospective studies are needed to better define the morbidity of post-HSCT BKV disease and inform the design of prophylaxis and treatment trials.

Kidney and bladder outcomes in children with hemorrhagic cystitis and BK virus infection after allogeneic hematopoietic stem cell transplantation

BK virus (BKV) infection is associated with hemorrhagic cystitis (HC) in hematopoietic stem cell transplantation (HSCT) recipients and nephropathy after kidney transplantation. We assessed the association between BKV and kidney and bladder complications in children developing HC by retrospectively reviewing 221 consecutive pediatric allogeneic HSCT recipients at the Children's Hospital of Philadelphia from 2005 to 2011. We included all patients with BKV PCR testing performed for clinical indication from day 0 until 1 year post-HSCT (N = 68). We assessed the association of any BKV infection (urine and/or blood) or peak BK viremia ≥ 10,000 copies/mL (high viremia) with severe HC (defined as grade IV-bladder catheterization or surgical intervention); the need for dialysis; serum creatinine-estimated glomerular filtration rate at the time of BKV testing, day 100, and day 365; and death. Children with high viremia more likely developed severe HC compared with those with peak viremia < 10,000 copies/mL (21% versus 2%; P = .02). BKV infection of the blood or urine was not associated with the need for dialysis, change in estimated glomerular filtration rate, or mortality. BKV infection is common after pediatric allogeneic HSCT, and plasma testing in those with HC may predict patients who will develop severe bladder injury.

BK virus nephropathy in a pediatric heart transplant recipient with post-transplant lymphoproliferative disorder: a case report and review of literature

BKV is known to cause allograft failure in kidney transplant recipients. It has been recently recognized to cause native kidney nephropathy in non-kidney transplant recipients. This is a case report BKVN in a 15-yr-old HTx recipient who had PTLD and a review of pediatric cases in the literature. The patient was diagnosed with BKVN +189 months after transplantation and died thirty days after diagnosis of BKVN. We identified five other cases of BKVN in pediatric non-kidney solid organ transplantation, of which all were HTx recipients. Overall, outcome was poor and BKV clearance was not achieved with reduction of immunosuppression and with current therapies. We strongly recommend that pediatric HTx recipients be tested for BKV infection if there is evidence of kidney dysfunction. We also recommend that they have an annual screening for BKV viruria and viremia with the assessment of kidney function.

BK polyoma virus nephropathy in the native kidney

BACKGROUND

While BK polyoma virus nephropathy (PVN) is a well-recognized cause of renal allograft dysfunction, PVN of native kidneys is likely under-recognized.

METHODS

We present the pathologic features, risk factors and outcomes of eight cases of PVN in native kidneys.

RESULTS

The cohort included eight males aged 16-73 years (mean 47.4) with an immunocompromised state (mean duration 3.15 years) attributable to: hematologic malignancies (n = 6), for which three had undergone bone marrow transplant; lung transplant (n = 1) and combined tuberculosis and diabetes (n = 1). Seven patients were receiving specific immunosuppressive therapies. Patients were biopsied for acute kidney injury (AKI) with rise in mean creatinine levels from baseline 1.6 to 2.8 mg/dL. Pathology showed BK PVN with characteristic intranuclear inclusions staining positive for SV40 T antigen and negative for JC virus (JCV), with positive serum and/or urine PCR for BK virus. One patient had focal medullary JCV co-infection. Two patients also had renal infiltration by chronic lymphocytic leukemia (CLL). Six patients received specific therapy directed to PVN (cidofovir or leflunomide). Follow-up ranged from 2 to 20 (mean 10) months. Despite marked decrease in serum BK viral copy numbers, creatinine continued to rise in six cases (mean 3.7 mg/dL in four, requiring dialysis in two) and three patients died of malignancy, opportunistic infection or renal failure. Advanced histologic stage of PVN, ineffective antiviral therapy, co-morbidities and persistent immunocompromised state likely contributed to the poor outcomes.

CONCLUSION

A high level of suspicion in immunocompromised patients is needed to diagnose PVN in an early stage that may respond more favorably to antiviral therapy.

Polyomavirus JC urinary shedding in kidney and liver transplant recipients associated with reduced creatinine clearance

BACKGROUND

Polyomavirus reactivation can cause significant morbidity in solid organ transplant recipients, particularly BK virus (BKV) in kidney transplant patients. Less is known about dynamics of John Cunningham virus (JCV) in nonkidney organ transplant patients.

METHODS

We examined the frequency of urinary shedding of polyomaviruses BKV and JCV and their relationship to creatinine clearance (CrCl) in a longitudinal study of 41 kidney and 33 liver transplant recipients.

RESULTS

Any polyomavirus urinary shedding was more frequent in liver than kidney recipients (64% vs 39%; P= .03). JCV was excreted more frequently by liver than kidney recipients (71% vs 38%), whereas BKV was shed more often by kidney than liver patients (69% vs 52%). Mean JCV loads were significantly higher than those of BKV in both patient groups (P< .0001). Lower mean CrCl values were significantly associated with JCV shedding in both kidney and liver recipients (P< .001).

CONCLUSIONS

These findings suggest that BKV and JCV display different patterns of reactivation and shedding in kidney and liver transplant patients and that JCV may have a role in renal dysfunction in some solid organ transplant recipients.

Renal dysfunction by BK virus infection is correlated with activated T cell level in renal transplantation

BACKGROUND

BK virus (BKV) is known to be associated with nephropathy. Here, we investigated the relationships between BKV levels, T-cell activation, and kidney function in kidney transplant recipients.

MATERIALS AND METHODS

In renal transplant patients and controls, urine BKV levels were detected by quantitative real-time PCR, and the percentage of activated T lymphocytes in blood was determined by flow cytometry. The correlations between viral load, activated T cell percentage, and renal function were determined.

RESULTS

Urine BKV viral loads and the activated T cell percentage were significantly elevated in transplant recipients. Correlational analysis indicated that transplant recipients that had BKV levels of more than 10(6) copies/mL and an activated T lymphocyte percentage of less than 20% were likely to have poor renal function.

CONCLUSIONS

Urine BKV levels and the percentage of activated T lymphocytes can be used as clinical indices to optimize the dosage of immunosuppressive drugs.

Chronic kidney disease after nonrenal solid organ transplantation: a histological assessment and utility of chronic allograft damage index scoring

BACKGROUND

It is proposed that chronic calcineurin inhibitor (CNI) nephrotoxicity has a central role in chronic kidney disease after nonrenal solid organ transplantation (NRSOT), although there are little data on renal histology in this setting. The aim of this study was to assess the histological features and renal outcomes of a cohort of patients with chronic kidney disease after NRSOT.

METHODS

Renal biopsies of 62 NRSOT recipients were evaluated for histological diagnoses. Biopsies were graded for chronic allograft damage index parameters and for arteriolar hyalinosis. The sum of all chronic allograft damage index parameters and arteriolar hyalinosis scores was called chronic damage index.

RESULTS

The biopsies were performed at a median of 4 (range: 0.3-15.9) years after NRSOT and at serum creatinine of 318±17.7 μmol/L (mean±standard deviation). Twenty-two (35.5%) biopsies showed predominant features of chronic CNI nephrotoxicity, 27 (43.5%) predominant features of hypertensive nephropathy, and 12 (19.3%) an alternative primary renal pathology. Twenty-four (38.7%) patients had progression to end-stage renal disease, at a median of 1.5 (0-10.1) years after biopsy and 6.9 (0.3-19.2) years after NRSOT. The risk of renal progression was associated with in situ damage measured by chronic damage index.

CONCLUSIONS

Although CNI nephrotoxicity is an important cause of renal failure after NRSOT, many patients do not have overt histological evidence of CNI toxicity. Quantitative parameters of chronic damage can stratify renal prognosis.

Assessment of infection with polyomaviruses BKV, JCV and SV40 in different groups of Cuban individuals

We investigated the frequency of BKV, JCV and SV40 reactivation in three groups of Cuban patients by multiplex nested PCR assay of 40 paraffin-embedded colorectal neoplasm tissues, 113 urine samples, and 125 plasma samples from 27 transplant recipients, and cerebrospinal fluid (CSF) from 67 HIV-1-infected individuals with central nervous system (CNS) disorders. None of these polyomaviruses were detected in colorectal neoplasms. JCV DNA was detected in 2 of 67 patients (2.9%) with CNS disorders, but neither BKV nor SV40 was identified. BKV was found in urine from 38.5% and 28.6% of adult and pediatric transplant recipients, respectively. In adult renal transplant recipients, excretion of BKV in urine was significantly associated with episodes of acute rejection (p=0.012) and with excretion of HCMV in urine (p= 0.008). In Cuba, the polyomaviruses studied here could not be related to colorectal neoplasms, and JCV was rarely detected in CSFs of HIV-1-infected individuals, whilst BKV reactivation was found to occur frequently in organ transplant recipients.

Evaluation and management of BK virus-associated nephropathy following allogeneic hematopoietic cell transplantation

BK virus nephropathy is a common cause of graft loss in kidney transplant recipients. Cases of BK nephropathy following allogeneic hematopoietic cell transplantation (HCT) are underreported. An increased incidence of BK virus-associated nephropathy is being seen in the setting of more profound and prolonged immunosuppression following solid organ transplantation and HCT. We will review diagnostic and treatment modalities for BK-associated nephropathy following allogeneic HCT.

BK polyomavirus infection and nephropathy: the virus-immune system interplay

Reactivation of latent BK polyomavirus (BKV) infection continues to be a major challenge in renal graft recipients. Progression of BKV infection to BKV-associated nephropathy (BKVAN) leads to graft loss in up to 60% of affected patients. Interestingly, although >80% of healthy adults are seropositive for BKV, BKVAN occurs almost exclusively in transplanted kidneys, which raises questions about its underlying pathogenetic mechanisms. Intragraft inflammation and an insufficient antiviral immune response seem to be the most important risk factors. Early studies revealed an association between the rate of recovery of BKV-specific cellular immunity (which shows high interindividual variation) and BK viral clearance, which determines the clinical course of BKV infection. In patients with prompt recovery of BKV-specific T cells, BKV infection can be controlled at the early reactivation stage and does not progress to BKVAN. By contrast, in patients with persistent BKV reactivation caused by insufficient BKV-specific immunity, continued viral replication and inflammation ultimately lead to graft injury and/or BKVAN. As the chronic course of BKV infection can be prevented in most patients by prompt restoration of BKV-specific immunity, frequent monitoring of BK viral load and targeted, timely modification or reduction of immunosuppression is strongly recommended for affected patients.

Reversible ureteral obstruction due to polyomavirus infection after percutaneous nephrostomy catheter placement

BK virus (BKV) is a human polyomavirus that remains latent in the urinary tract epithelium in most individuals. However, in immunocompromised states, including after hematopoietic stem cell transplantation (HSCT), BKV may reactivate and cause infection predominantly affecting the bladder, commonly manifested as hemorrhagic cystitis. Renal insufficiency, occasionally requiring hemodialysis, is not uncommon and was previously attributed to medications or the development of tubulointestitial nephritis. We report a series of 6 HSCT recipients who developed obstructive uropathy of the upper urinary tract system secondary to inflammation and hemorrhage involving the upper uroepithelium, causing ureteral stenosis. Temporary placement of a percutaneous nephrostomy catheter relieved the obstruction and significantly improved kidney function, successfully preventing progression to more advanced renal disease in these patients.

BK virus nephropathy in a pediatric autologous stem-cell transplant recipient

BK virus (BKV) is an increasingly identified cause of pathology in immunocompromised transplant recipients. BKV is a well-known cause of graft dysfunction following renal transplantation and has also been reported in the native kidneys of other solid organ recipients. Less commonly, BKV nephropathy occurs in allogeneic stem-cell transplant (SCT) recipients. We now describe the first reported case of BKV nephropathy after pediatric autologous SCT.

Renal failure five years after lung transplantation due to polyomavirus BK-associated nephropathy

Polyomavirus-associated nephropathy (PyVAN) is rare in nonrenal solid organ transplantation and only limited information is available from single cases. We describe a 67-year-old female presenting with hypertension and progressive kidney failure due to PyVAN 60 months after lung transplantation. Plasma BK virus (BKV) loads were 4.85 log¹⁰ copies/mL at diagnosis and cleared slowly over 14 months after switching from tacrolimus, mycophenolate and prednisone to low-dose tacrolimus, sirolimus and leflunomide, the latter being discontinued for anemia and diarrhea. BKV- and JC virus-specific immunoglobulins were detectable prior to transplantation. Only BKV-specific IgG and IgM increased during follow-up. BKV-specific T cells were detectable in blood following in vitro expansion, but cleared with reincreased sirolimus, yet BKV viremia remained undetectable. We identified eight other cases of PyVAN in nonrenal solid organ transplantation including lung (n = 1), heart (n = 6) and pancreas (n = 1). Overall, diagnosis was later than commonly seen in kidney transplants (median 18 months, interquartile range 10-29). Seven patients were male, five received triple immunosuppression consisting of tacrolimus, mycophenolate, prednisone. Immunosuppression was reduced in four cases and cidofovir and/or leflunomide administered in five and two cases, respectively. Renal function deteriorated in five requiring hemodialysis in four. We discuss mTOR inhibitors versus cidofovir and leflunomide as potential PyVAN rescue therapy.

A correlation between polyomavirus JC virus quantification and genotypes in renal transplantation

OBJECTIVE

To determine whether the John Cunningham virus (JCV) viral load and the multigenotypes in viruria are correlated with transplant patients.

METHODS

The urine of 60 renal transplant patients and 60 healthy controls were screened. We used quantitative real-time polymerase chain reaction and capillary electrophoresis to assess viral load and genotype respectively.

RESULTS

The incidence of viruria and viral load were higher in transplant patients with P = .0092 and P = .0094, respectively. The incidence of different genotype in transplant patients versus controls was 8.3% versus 13.3% for single genotype, 26.7% versus 5% for 2 genotypes, and 5% versus 0% for multigenotypes (P = .0004). The incidence of more than 2 genotypes was high in people with a high viral load and closely related with the transplant patients (P = .007).

CONCLUSIONS

Not only viral load but also genotypes are important as a screening parameter to understand the immune milieu of the patients to prevent subsequent complications like polyomavirus nephropathy, infection, and malignancy.

Native BK viral nephropathy in a pediatric heart transplant recipient

BK viral nephropathy is a well-documented clinical entity in kidney transplant recipients and a significant cause of morbidity and allograft loss in affected patients. BK viral nephropathy in native kidneys of non-kidney transplant recipients is relatively uncommon, but has been reported in adult patients. We report the occurrence of BK viral nephropathy in a pediatric heart transplant recipient. A 10-yr-old boy with past history of Ewing's sarcoma underwent heart transplantation for dilated cardiomyopathy induced by previous chemotherapy with doxorubicin. Post-transplant course was complicated by grade 3A rejection and CMV colitis. He was diagnosed with native BK viral nephropathy approximately 18 months post-transplant due to mild, but persistent, elevation in serum creatinine associated with proteinuria. BK viral nephropathy affects non-kidney transplant recipients, and a high index of suspicion is necessary for early diagnosis and management of this condition.

BK virus nephropathy in the native kidneys of a pediatric heart transplant recipient

BK virus is a human polyoma virus that may cause nephropathy in immunosuppressed patients. It is a well-recognized cause of renal allograft dysfunction and allograft loss in renal transplant recipients, but it is an infrequent cause of nephropathy outside this setting. There are a few case reports of BK virus nephropathy in the native kidneys of immunosuppressed adult patients with non-renal transplants, but so far it has not been reported in pediatric non-renal solid organ transplant recipients. We report a case of a seven-yr-old heart transplant patient who was diagnosed with BK virus nephropathy, eight months after his second heart transplant. Despite intervention, his renal dysfunction progressed to renal failure. He is currently receiving maintenance hemodialysis and awaiting renal transplantation. It is important to recognize BK virus infection as a possible cause of renal dysfunction in immunosuppressed children who are non-renal transplant recipients.

Prevalence of polyomavirus viruria (JC virus/BK virus) in children following liver transplantation

BKV infection is a potential cause of renal dysfunction in non-renal organ transplant recipients. JCV is the causative agent of PML. Furthermore, polyomaviruses are tumor inducing viruses and molecular data suggest an association with malignancies among solid organ transplant patients. So far, there are no studies analyzing polyomavirus viruria following Ltx in children. We performed a prospective prevalence study at a mean of 2187 (range 20-5671) days after transplantation in 100 consecutive children admitted for the routine follow-up examination post-Ltx. The urine was screened for BKV and JCV DNA by using PCR in each case. A plasma analysis by PCR was also done if more than 100,000 DNA copies/mL urine were detected. BKV or JCV viruria was found in 19% (n = 19) of our patients. All patients were free of clinical signs of viral infection, PML, or nephropathy. GFR was normal in 97% of patients and we found no statistical difference of kidney function between patients with and without BKV/JCV viruria. The extent of immunosuppressive therapy had no influence on the polyomavirus viruria. Overall, we found a higher prevalence of polyomavirus viruria in our pediatric liver transplant recipients than reported in adult patients.

BK nephropathy in pediatric hematopoietic stem cell transplant recipients

BK nephropathy is a known cause of renal insufficiency in kidney transplant recipients. Activation of the polyoma virus may also occur in the native kidneys of non-renal allograft recipients. BK nephropathy has only been reported in a few patients after HCT, most being adult patients, and the single reported pediatric case had evidence of hemorrhagic cystitis. The response to antiviral therapy also seems to differ widely. Here, we describe two cases of BK nephropathy in the native kidneys of HCT recipients exposed to high levels of immunosuppression because of GVHD. Neither of our patients had any evidence of hemorrhagic cystitis. We present definitive renal pathology and detailed chronological evidence of the rising serum creatinine with simultaneous serum and urine BK PCR titers. In one of our cases, antiviral therapy did not seem beneficial as documented by continued renal dysfunction and elevated serum/urine BK PCR titers. Based on our report, intense immunosuppression in pediatric HCT recipients seems to be involved in the activation of BK virus and BK nephropathy should be suspected even in the absence of hematuria in HCT recipients with unexplained renal dysfunction.

BK virus in liver transplant recipients: a prospective study

BACKGROUND

BK virus (BKV) is a polyomavirus that is associated with nephropathy and graft loss among kidney transplant recipients. The role of BK virus in nonrenal solid organ transplant recipients has not been clearly established; only anecdotal case reports have been published.

METHODS

From August 2005 to September 2007, all liver transplant (OLT) recipients who gave their consent were enrolled in this prospective longitudinal study. BK viral load was measured using real-time quantitative polymerase chain reaction assays of urine and plasma, using samples collected at week 1 and months 1, 3, 6, 9, 12, 15, 18, 21, and 24 posttransplantation. We also collected demographic and clinical data, including serum creatinine and immunosuppressive therapy.

RESULTS

The mean age of the 62 patients was 51.4 years including 14 (22.5%) women. Hepatitis C infection was present in 24 patients (38.7%). BK viruria was detected in 14.5% of 290 samples, corresponding to 13 patients (21%). BK viremia was detected in 5.1% of 317 samples, corresponding to 11 patients (18%). Almost all cases of BK viremia (91%) occurred in the first 3 months after OLT. BKV viremia was more common among patients experiencing a rejection episode (10.6 vs 40%, P = .01). We did not observe a relationship between single episodes of BKV replication and renal function: median plasma creatinine 1.1 mg/dL in patients without versus 1.2 mg/dL with BKV viremia. The three patients with persistent viremia displayed renal insufficiency; one of them died due to multiorgan failure of unknown origin.

CONCLUSIONS

BKV is frequently detected in OLT recipients (viruria 21% and viremia 18%) early after transplantation. It is more common among patients with rejection episodes. Persistent BKV viremia may be related to renal dysfunction in OLT patients.

BK virus infection is associated with hematuria and renal impairment in recipients of allogeneic hematopoetic stem cell transplants

BK virus (BKV) is an important pathogen and cause of nephropathy in renal transplant recipients, but its significance following hematopoetic stem cell transplantation (HSCT) is less well described. We measured blood and urine BKV in 124 allogeneic HSCT patients (67 had undergone prior HSCT [surveillance cohort]; 57 were monitored from transplant day 0 [prospective cohort]). BK viruria was manifest in 64.8% of the patients; 16.9% developed viremia. In the prospective cohort, the median time from transplantation to BK viremia development (128 days) was longer than for viruria (24 days; P < .0001). Among clinical factors (sex, disease, transplant type, alemtuzumab use, cytomegalovirus [CMV] viremia, graft-versus-host disease [GVHD], donor HLA C7 allele), only CMV viremia was more common in patients with BKV infection (P < or = .04). There was a direct relationship between blood and urine BKV levels and the occurrence, and degree, of hematuria (P < or = .03). Finally, BKV infection was analyzed along with other clinical factors in relation to the development of post-HSCT renal impairment. On multivariate analysis, only BK viremia (P=.000002) and alternative-donor transplantation (P=.002) were independent predictors of development of post-HSCT renal impairment, with BK viremia associated with a median 1.62mg/dL rise in creatinine from the pretransplant baseline. Among 8 patients in the surveillance cohort with BK viremia, 2 developed biopsy-proven BKV nephropathy requiring hemodialysis. Investigation of whether prophylaxis against, or treatment of, BKV in the post-HSCT setting mitigates the associated morbidities, especially kidney injury, warrants prospective evaluation.