BK virus nephropathy (BKVN) is a recognized cause of graft failure in kidney transplant recipients. There are limited data on the epidemiology of BK virus (BKV) infection after alemtuzumab induction. By clinical protocol, the kidney transplant recipients at our center were screened with BKV plasma PCR monthly for the first 4 months posttransplant then every 2–3 months for 2 years. A single center retrospective cohort study of all kidney transplant recipients from January 2008 to August 2010 was conducted to determine incidence and outcomes of BKV infection. Descriptive statistics and Kaplan–Meier analysis was performed. Of 666 recipients, 250 (37.5%) developed viruria, 80 (12%) developed viremia and 31 (4.7%) developed BKVN at a median of 17, 21 and 30 weeks, respectively. Induction with alemtuzumab did not significantly affect incidence of BKVN. Increased recipient age, African American race, acute graft rejection and CMV infection were significantly associated with the development of BKVN in multivariate analysis. The incidence of BK viruria, viremia and nephropathy was not significantly different among kidney transplant recipients who received alemtuzumab induction compared to patients receiving less potent induction.
BK virus nephropathy (BKVN) is a challenge in the contemporary era of kidney transplantation. Epidemiologic studies estimate that BK viruria, viremia and nephropathy occur in 30%, 13% and 8% of patients at 16, 23 and 28 weeks after renal transplantation, respectively . Only 2 of 21 epidemiologic studies have evaluated BKV infection as a primary endpoint in the setting of alemtuzumab induction and these studies were unable to elucidate specific risk factors for BKVN [2, 3]. As a result, the relative impact of this potent lymphocyte-depleting agent on the epidemiology of BKVN remains poorly defined.
The cellular immune system plays a crucial role in controlling BKV replication. Deficiencies of BK-specific T cell immunity are strongly correlated with the development of BKVN . Induction with alemtuzumab, a humanized monoclonal antibody against CD52, induces pan-T cell depletion, which may persist for 2 years posttransplantation. Given the importance of cellular immune response on BKVN and the prolonged impairment of this response, transplant patients who receive alemtuzumab would be expected to have an increased incidence of BKVN and/or a more late-onset BKVN. However, previous epidemiologic studies evaluating BKVN as a secondary endpoint after alemtuzumab induction have reported conflicting results [5-9]. As our center has one of the largest experiences with alemtuzumab induction for kidney transplantation, we conducted a single center retrospective cohort study to define the incidence and outcomes of BKV infection.
Since 2008, all kidney transplant recipients have been screened for BKVN by plasma polymerase chain reaction (PCR) monthly for the first 4 months posttransplant, every 2 months for the remainder of the first year, then every 3 months in year 2. Plasma BKV PCR was also performed when recipients had an increase in serum creatinine (Cr) and/or when a kidney biopsy was performed. The performance of urine BKV PCR and the management of patients with detectable BK PCR or BKVN, including changes in immunosuppression, were at the discretion of the treating physician.
Transplant surgery specifics
All kidney and simultaneous pancreas-kidney (SPK) transplant patients received one 30 mg dose of alemtuzumab for induction in addition to a rapid steroid taper, unless they were infected with hepatitis C virus (HCV) or human immunodeficiency virus (HIV) or had a history of cancer with a high risk of recurrence . Ureteral stents were used in all of the patients and were removed 6 weeks posttransplant. Patients with allergic reactions to sulfa received atovaquone for 12 months plus ciprofloxacin for urinary tract infection prophylaxis while ureteral stents were in place (see supplement for additional management details).
Protocol kidney biopsies, performed at 3, 12 and 24 months posttransplant and for cause, were routinely stained for the SV40 large-T antigen.
Following Institutional Review Board approval, we conducted a single center retrospective cohort study of all patients over 18 years of age who received a kidney or multiorgan transplant with a kidney from January 2008 through August 2010. Each patient's electronic medical record was reviewed to collect recipient information including demographics, immunosuppressive medication regimens and rejection episodes. Onsets of BK viruria, BK viremia and BKVN were co-primary endpoints. BK viruria was defined as any detectable urine BKV PCR; BK viremia was defined as any detectable plasma BKV PCR; BKVN was defined by biopsy with SV40 staining consistent with BKV infection. Graft loss, defined as return to dialysis, and death were secondary endpoints.
Student's t-test, Fisher's exact or Pearson's chi-square tests were performed where appropriate. Univariate analysis was performed using the Kaplan–Meier method with the log-rank test and multivariate analyses were performed using the Cox proportional hazards model. Variables with a p-value < 0.1 in univariate analysis were included in the multivariate model and the hazard ratio estimates were based on simultaneous analysis of all independent variables. Assumption of proportionality was tested using log-minus-log plot and was met. All analyses were conducted using SAS 9.2 (SAS Inc., Cary, NC, USA). A two-sided p-value of <0.05 was considered statistically significant.
Seven hundred forty-two patients underwent kidney transplantation between January 2008 and August 2010. After excluding patients without any BKV screening performed at the time of the chart review (n = 70), who died within 1 month of transplant (n = 1), and who received a combined stem cell-kidney transplant (n = 5), 666 patients were included (Table 1), 80.6% (537) of whom received alemtuzumab induction. Adherence to our screening protocol was poor, with a median of 3 (range 0–32) of the expected 8 BKV PCR results available per patient. There was no difference in protocol adherence between patients who did and did not receive alemtuzumab (median plasma BKV PCR: 3 [0–28] vs. 3 [0–32]). Thirty-five patients did not have BKV PCR sent until after the first year posttransplant. Recipients adhered to the kidney graft biopsy protocol approximately 70% of the time, without noted difference between risk groups.
Two hundred fifty patients (37.5%) developed BK viruria at a median of 16.7 weeks (range 0.1–115.7 weeks) posttransplant, 80 patients (12%) developed BK viremia at a median of 21.1 weeks (range 4.1–108.7 weeks) and 31 patients (4.7%) developed biopsy-proven BKVN at a median of 29.9 weeks (range 8.9–91 weeks; Table 2). Of the 80 patients who developed viremia, 3 did not have urine assessed for viruria. Of the 31 patients who developed BKVN, 1 did not have BKV detected by urine or plasma PCR. Fifteen (48.4%) of the 31 BKVN cases were diagnosed by protocol biopsy. Twenty-one (67.7%) of the BKVN diagnoses were pathologic stage A.
Table 2. Characteristics of patients by disease state
Sustained viruria (two detectable urine BKV PCR at least one week apart) was associated with BK viremia and BKVN (p < 0.001 when compared to transient viruria). No patient with transient viruria developed viremia or BKVN and only 1 patient with transient viremia developed BKVN. Sustained viremia was also associated with BKVN development when compared to transient viremia (p = 0.002). Sustained viruria had a sensitivity of 90.3%, specificity of 80.2%, positive predictive value of 18.2% and negative predictive value for 99.4% for BKVN. Sustained viremia had a sensitivity of 80.6%, specificity of 95.4%, positive predictive1 value of 46.3% and negative predictive value for 99% for BKVN.
Risk factors for development of BKV disease
Older recipient age (p = 0.006), African American race of the recipient (p = 0.011), deceased donor kidney transplant (p = 0.038), multivisceral transplant (SPK, simultaneous liver-kidney and heart-kidney; p = 0.031), extended criteria donor use (p = 0.009), high degree of HLA mismatch (p = 0.002), use of granulocyte-colony stimulating factor (G-CSF; p = 0.036) and CMV infection (p ≤ 0.001) were all associated with the development of BKVN by univariate analysis (Table 2). Although patients with HIV and HCV received basiliximab induction instead of alemtuzumab, there was not a difference in BKV-related endpoints in patients with and without chronic viral infections (i.e. HIV, hepatitis B virus [HBV], HCV, Epstein–Barr virus [EBV]/posttransplant lymphoproliferative disorder; Table 2).
Recipients with graft rejection episodes had a 17.7% higher rate of BK viruria (p < 0.001), 22.7% higher rate of BK viremia (p < 0.001) and 39% higher rate of BKVN (p < 0.001) (Table 2). When cellular and humoral rejection were evaluated separately, cellular rejection remained significantly associated with BKV endpoints, but humoral rejection was only significantly correlated with viruria (Table 2). Rejection occurred before viruria in 37/100 (37%) cases at a median of 14 (0–66) weeks before. Rejection preceded viremia in 12/36 (33%) cases at a median of 12 (0–50) weeks before. Rejection preceded BKVN in 6/19 (32%) cases at a median of 11 (0–51).
Of the 57 patients with sulfa allergies who received ciprofloxacin prophylaxis for the first 6 weeks after transplant, 33.3% developed BK viruria, 3.5% developed BK viremia and no patient developed BKVN. Ciprofloxacin exposure correlated with less BK viremia (p = 0.049). Although no patients on ciprofloxacin prophylaxis developed BKVN, this finding did not reach statisticalicance.
Kaplan–Meier analysis (Figure 1) demonstrates that the 1-year actuarial posttransplant rate of BK viruria, BK viremia and BKVN was 35%, 11% and 4%, respectively. Our Kaplan–Meier estimates of the probability of developing BK viremia and BKVN at 2 years were 16% (95% CI: 12–20%) and 7% (95% CI: 4–10%), respectively, which yielded no statistical difference than what was reported by Hirsch et al. [13% (95% CI: 5–21%) and 8% (95%CI: 1–15%), respectively] . Since viruria was measured using decoy cells in the Hirsch study, but measured with PCR in this study, we did not compare our rates of viruria.
In the univariate survival analysis, older age, African American race, deceased donor, multiorgan transplant, ECD donor, HLA mismatch, rejection and CMV infection were all associated with greater hazard of developing BKVN. However, only increased recipient age (HR 1.04, 95% CI 1.00–1.07, p = 0.048), African American recipient race (HR 2.89, 95% CI 1.36–6.14, p = 0.006), acute graft rejection (HR 3.18, 95% CI 1.42–7.12, p = 0.005) and CMV infection (HR 2.72, 95% CI 1.19–6.24, p = 0.018) remained significantly associated with the development of BKVN in the multivariate Cox regression analysis (Table 3).
Table 3. Univariate and multivariate models assessing association of patient characteristics with BKVN
Only variables with p < 0.1 in the univariate analysis were included in the multivariate analysis.
Abbreviations: AA = African American; BKVN = BK virus nephropathy; CMV = cytomegalovirus; ECD = extended criteria donor; GCSF = granulocyte colony stimulating factor; HLA = human leukocyte antigen.
Cold ischemic time
In patients who developed BK viremia, urine BK viral loads were significantly higher (8.7 ± 2.7 vs. 6.5 ± 2.2 log10 copies/mL, p = <0.001), although Cr at viruria diagnosis was not higher (1.6 ± 0.6 mg/dL vs. 1.5 ± 0.9 mg/dL, p = 0.281; Figure 2). In those who developed BKVN, both plasma BK viral loads (6.3 ± 1.5 vs. 5.2 ± 1.7 log10 copies/mL, p = 0.003) and Cr at viremia diagnosis were notably higher (2.0 ± 0.7 mg/dL vs. 1.5 ± 0.6 mg/dL, p = 0.001) than those who did not develop BKVN (Figure 3). Mean urine and plasma BK viral loads at histologic BKVN diagnosis were 9.6 ± 2.6 and 5.1 ± 3.1 log10 copies/mL, respectively. Mean urine and plasma viral loads in patients who developed BKVN are depicted in Figure 4.
The mean peak plasma viral load was similar in both the alemtuzumab and nonalemtuzumab induced groups (6.2 ± 1.9 vs. 6.9 ± 2.1 log10 copies/mL). Furthermore, the time from peak plasma BK viral load to clearance of viremia was not statistically different in these two groups (12.1 ± 12.2 weeks vs. 19.5±20.5 weeks, p > 0.5).
Details about BKV treatment can be found in the supplemental materials.
Patient and graft outcomes
Of the 666 kidney transplant recipients, 38 (5.7%) had kidney graft failure (6 from BKVN and 11 from rejection) and 27 (4.1%) died from an unrelated cause (59.3% with a functioning graft; see Table 4). Of the 31 patients who developed BKVN during the study period, 6 (19.4%) lost their graft due to BKVN. BK viremia (23.7% vs. 11.3%, p = 0.036), BKVN (21.1% vs. 3.7%, p ≤ 0.001), rejection (68.4% vs. 26.6%, p ≤ 0.001) and CMV infection (34.2% vs. 8.8%, p ≤ 0.001) were more common among patients who lost graft function. The course of the six patients with graft loss due to BKVN is outlined in more detail in Table 5. Kaplan–Meier analysis in Figure 5 illustrates the significantly decreased graft survival in patients with BKVN as compared to patients without BKV replication, and those with BK viruria or viremia alone (χ2 = 12.01, p = 0.0074).
Table 4. Patient and graft outcomes
All patients (n = 666)
No replication (n = 412)
Viruria (n = 250)
Viremia (n = 80)
BKVN (n = 31)
Etiology of graft loss was clinically defined by the transplant team at the time of allograft loss.
Causes of graft failure: sepsis/multi-system organ failure (6), focal segmental glomerulosclerosis (5), acute tubular necrosis (3), other local infection (3), glomerulonephritis (2), amyloidosis (1), hemolytic uremic syndrome (1), unknown (1).
Etiology for graft loss was defined by the transplant team using the patient and graft-specific information; Repeat graft biopsies performed a median of 31 days (0–201 days) before graft loss and 4/6 had residual cytopathic effect consistent with BKVN.
Abbreviations: AA = African American; C = Caucasian; H = Hispanic; ECD = extended criteria donor; LUKT = living unrelated kidney transplant; SPK = simultaneous pancreas kidney transplant; ALM = alemtuzumab; BAS, basiliximab; FK = tacrolimus; MMF = mycophenolate mofetil; Pred = prednisone; Cr = creatinine; CID = cidofovir; IS dec = immunosuppression decreased; LEF = leflunomide.
IS dec, CID
IS dec, CID
IS dec, CID
IS dec, CID, LEF
IS dec, CID
IS dec, CID
This is the largest study to primarily describe the epidemiology of BKVN in alemtuzumab-induced kidney recipients. Among our patients, over a third (37.1%) developed BK viruria after 4 months posttransplant, 12% developed BK viremia after 5 months and 5% developed biopsy-proven BKVN at 7 months. Despite differences in induction, nearly all of our patients received tacrolimus and MMF with similar trough levels for maintenance immune suppression, providing greater homogeneity in our population than in other study cohorts, strengthening the validity of our findings. In the available studies evaluating alemtuzumab induction in adult kidney transplantation, results have been conflicting as to whether alemtuzumab is associated with increased risk of the development of BKVN ([2, 3, 5-9, 11-13]; Table 6). BKVN was usually a secondary endpoint of these studies.
Table 6. Summary of studies including adult alemtuzumab-induced kidney transplant patients
Author, year of publication, (reference)
Study group or Comparison
Abbreviations: ALM = alemtuzumab; AR = acute rejection; ATG = antithymocyte globulin; BAS = baxiliximab; DAC = daclizumab; DCD = donation after cardiac death; SPK = simultaneous pancreas -kidney transplant.
Denotes BKV infection was a secondary endpoint of the study.
Only study to evaluate risk factors for BKV infection: Univariate analysis revealed no significant risk factors associated with BK viremia.
Note: BK viremia increased risk for AR (HR 3.48; 95% CI 1.24–9.76; p = 0.018).
Describe the incidence BKV infection after ALM induction
BK viremia: 6.6% incidence BKVN: 0.2% incidence
We found a similar incidence and onset of BKV disease as previous studies that included no or few patients with alemtuzumab induction [1, 14]. Specifically, our findings are similar to those reported by Hirsch and colleagues in their sentinel paper of BKV epidemiology despite only five patients receiving antithymocyte globulin (ATG) and no patient receiving alemtuzumab in the Hirsch cohort . Therefore, although we hypothesized that alemtuzumab would delay onset of BKV replication, this does not appear to be the case.
Our data on BKV dynamics support the existing literature, as urine and plasma BK viral loads at BKVN diagnosis were comparable to levels reported in the literature [1, 15]. In addition, patients who developed viremia had higher levels of virus in their urine and urine viral loads were always higher than those in the plasma .
In addition, our data confirms that older recipient age and acute rejection are associated with development of BKVN [1, 14]. We also found African American recipient race to be associated with a higher rate BKVN without an increased risk for viruria and viremia. A recent prospective study found that African American race protected against the development of BK viruria and viremia, therefore,
relationship between race and BKV disease is an important element to be included in future research . Further, although HLA mismatch was significant in our univariate analysis, it did not remain so after controlling for other factors, including acute rejection. Finally, CMV infection was also significantly associated with the development of BKVN in our cohort, which has rarely been reported in the literature. Since both infections will reactivate in the setting of immune suppression , this association may be a marker of the impact that alemtuzumab has on cellular immune responses.
Although graft loss from BKVN ranges widely in the literature (0 to > 50%), aggressive screening combined with reduction of immunosuppression is associated with the best outcomes [14, 18, 19]. The high rate of graft loss attributable to BKVN (6 BKVN-attributed graft loss of 31 (19.4%) patients with BKVN) in this study could be the result of alemtuzumab, compliance with screening, or management choices for patients with BKVN. If alemtuzumab prevented the development of BKV-specific T cell responses, reduction of immunosuppression may fail to control viral replication in our patients. The short interval between detection of BKV in urine or blood and the biopsy-proven diagnosis of BKVN suggests a missed opportunity for early intervention and supports enhancing compliance with our screening protocol (Table 5). Using multiple interventions, we are working to increase compliance with the protocol and will assess the impact this has on detection and outcome of BKVN.
One patient in this cohort was diagnosed with early BKVN by biopsy, but never had a detectable urine or plasma BK viral load despite multiple assays performed. Possible reasons for this anomaly include nephropathy from JC virus, false positive pathology examination of the kidney biopsy or false negative PCR. There was no intervention after the BKVN diagnosis and the patient remained with a stable Cr; therefore, JC virus nephropathy is unlikely.
Our study does have limitations. First, it is a retrospective study, which allows us to only assess associations and not prove causation. As with all retrospective studies, there is the possibility for confounding variables that are not accounted for by our analyses. Second, the comparator group of patients receiving nonlymphocyte depleting induction therapy was small (∼20% of our population); we include our non-alemtuzumab-induced patients in this study as a point-of-reference only. Similarly, since our protocol generally defined which patients would not receive alemtuzumab, bias may have been introduced. We evaluated the effect of chronic viral infection and multiorgan transplantation on BKV endpoints in an effort to address this potential for bias. Third, some of the findings could be center-specific since this is a single center study. Fourth, patients generally had few screening plasma BK viral load measurements suggesting that screening may have been incomplete, which limits our ability to make strong conclusions regarding timing and duration of BK viral replication. BKV PCR was usually performed at our in-hospital laboratory, but sometimes performed at an outside lab. As BKV PCR assays are not standardized, it remains difficult to compare BK viral loads between patients and between studies. Finally, BKV treatment was not standardized, so we cannot make strong assessments about the specific role of any of these interventions in the management of BKVN.
In conclusion, this is the largest study primarily focused on the epidemiology of BKV-related disease in alemtuzumab-induced kidney transplant patients. These data suggest that alemtuzumab does not increase rates of BK viruria, viremia or BKVN and does not delay onset of BKV reactivation. The relatively high rate of graft loss in this study suggests that the optimal management of BKVN in alemtuzumab-induced patients, as in other patient populations, has yet to be defined; more frequent screening may be needed in this population. A prospective study to specifically compare BKV-related outcomes in kidney transplant patients receiving lymphocyte-depleting induction therapy versus nonlymphocyte depleting therapies should be performed. In addition, studies are needed to optimize the management of BKVN to further improve outcomes of patients with this disease.
Nicole Theodoropoulos and Daniela Ladner are funded, in part, through the Northwestern University Transplant Outcomes Research Collaborative (NUTORC). We thank Aimee Mandapat, MD, for her assistance in data collection.
The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.