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Volume: 21 Issue: 10 October 2023



Effect of Leflunomide on Treatment of Pediatric Renal Transplant Recipients With BK Virus Infection


Objectives: Infection with the BK virus is a significant complication after renal transplant and can progress to BK virus nephropathy and graft dysfunction. There is no consensus on the management of BK virus infection in pediatric renal transplant recipients. The most common therapeutic option is immunosup-pression reduction, which can increase rejection risk. We aimed to examine the effect of leflunomide, an agent with antiviral and immunosuppressive actions, in a case series of pediatric renal transplant recipients with BK virus infection.
Materials and Methods: Routine screening with blood BK virus DNA polymerase chain reaction was performed regularly in all of our renal transplant patients. When BK virus was detected, we reduced tacrolimus levels, discontinued mycophenolate mofetil, and started active treatment with leflunomide. Treatment with leflunomide was continued until BK virus was undetectable by polymerase chain reaction in at least 2 blood samples 2 weeks apart.
xResults: All pediatric patients developed BK virus infection in a mean period of 3.9 months after transplant. Graft dysfunction was evident in all patients with 20% to 100% elevation of creatinine from baseline. After leflunomide initiation, all patients had undetectable levels of BK virus by plasma polymerase chain reaction in at least 2 different samples within a mean period of 3.4 months, and renal function had normalized back to the baseline. None of our patients had evidence of hepatotoxicity or anemia on regular monitoring, with no other adverse events. Renal function remained stable in the follow-up period with no reoccurrence of BK viremia up to the date of this writing.
Conclusions: Treatment with leflunomide resulted in rapid BK virus clearance and preservation of renal function with no adverse effects.

Key words : Graft dysfunction, Immunosuppression, Living related kidney transplant, Renal transplantation


In recent years, optimization of immunosuppressive regimens in renal transplantation has been associated with an increased infection risk, especially with opportunistic organisms like the BK virus (BKV).1 The BK virus is a human polyomavirus that causes usually asymptomatic infection during childhood and remains afterward in a latent phase in the urothelium and renal tubular cells.2 BK virus can be reactivated following kidney transplant and detected with polymerase chain reaction (PCR) in urine (BK viruria) or in blood (BK viremia). BK virus can be also detected in the renal graft parenchyma by causing BKV nephropathy (BKVN).3 BK virus nephropathy manifests as tubulointerstitial nephritis, tubular atrophy, and fibrosis, which lead to deranged graft function and increased risk of graft loss.4

The most common intervention on the mana-gement of BKV infection in renal transplant recipients is reduction of immunosuppression.5 This strategy encounters the risk of rejection, especially in patients with increased rejection risk. With regard to additional therapeutic interventions, leflunomide, intravenous immunoglobulin G (IVIG), sirolimus, and ciprofloxacin have been used as active treatment with nonconclusive results in the literature so far.6

Leflunomide, an agent with immunosuppressive properties, is used widely in patients with rheumatoid arthritis. In vitro studies have shown that leflunomide inhibits BKV DNA replication in renal tubular epithelial cells.7 However, the efficacy of leflunomide in the treatment of BKVN in renal transplant recipients remains unknown.8

Our report aims to describe the safety and efficacy of active treatment of BKV with leflunomide in a small cohort of renal transplant recipients.

Materials and Methods

For the 4-year period 2018-2021, we performed routine screening with blood BKV DNA PCR for all of our renal transplant patients at months 1, 2, 3, 4, 5, 6, 9, 12, 18, and 24 after transplant. We diagnosed BK viremia if patients had a viral load >215 IU/mL in plasma PCR tests performed 2 weeks apart. All of our patients had received transplant induction treatment with basiliximab and maintenance immunosuppression with the triple regimen of tacrolimus, mycophenolate mofetil (MMF), and steroids.

All cases of confirmed BK viremia were managed with discontinuation of MMF and commencement of leflunomide. Because there is no clear dose recommendation for children with BKV infection, we followed the dosing scheme recommended for juvenile idiopathic arthritis as follows: 10 mg every second day for patients up to 20 kg; 10 mg/day for 20 to 30 kg; 10 mg/day alternating with 20 mg/day for 30 to 40 kg; and full adult dose of 20 mg/day for patients ≧40 kg.9 Tacrolimus trough levels were maintained at <6 ng/dL. We monitored BK viremia with PCR blood tests every 2 weeks. All patients had regular screening with full blood count and liver enzymes to monitor for adverse events such as liver enzyme elevation, anemia, and thrombocytopenia.

This study was approved by the ethics committee of our institution before it began and conforms to the ethical guidelines of the 1975 Helsinki Declaration. Written informed consent was obtained from our patients’ guardians for this publication.


Case 1

A 15-year-old renal transplant recipient had primary diagnosis of renal dysplasia after birth. She had developed end-stage renal failure at the age of 4 years and started on peritoneal dialysis. At the age of 7 years, she was switched to hemodialysis. She had received a living related transplant at the age of 13 years from her father. The donor tested positive for EBV and CMV, and the recipient’s test was negative for both. The recipient was hypersensitized; therefore, she received rituximab before transplant and induction treatment with basiliximab. She continued on maintenance treatment with tacrolimus, MMF, and methylprednisolone.

Three months after transplant she presented with hemorrhagic cystitis. Ultrasonography of the graft showed irregularly thickened bladder wall and increased transmural vascularity. Bladder mucosa biopsy via cystoscopy showed inflammatory changes, granulomatosis, ulceration, and eosinophilic infiltrates. There was also extended urothelium apoptosis and nuclei edema of the remaining urothelial cells. Immunohistochemistry was positive for BKV. Blood PCR was also positive for BKV (66793 IU/mL) and gradually increased to a highest viral load of 532210 IU/mL. Her creatinine increased from a baseline of 0.8 mg/dL to a maximum 1.6 mg/dL. Decoy cells were present in urine.

The MMF was stopped, and treatment with leflunomide was initiated. Tacrolimus levels were maintained between 4 and 6 ng/mL. After this regimen was initiated, renal function gradually improved and returned to baseline after 3 months; therefore, we did not proceed with a renal biopsy. Titers of BK virus were monitored with PCR every 2 weeks, and 4 months after treatment she had 2 consecutive PCR blood tests that were negative for BKV, which indicated BKV clearance. Leflunomide was stopped, and MMF was restarted. During the time she was treated with leflunomide, she had regular laboratory monitoring including full blood count and transaminase levels, and we observed no evidence of drug-induced adverse events.

Case 2

A 10-year-old boy had steroid-resistant nephrotic syndrome due to homozygous PLCE1 (c.3736C>T) sequence variation. He had started hemodialysis at the age of 2 years, and he had received a deceased donor renal transplant at the age of 8 years. The donor was negative for CMV and positive for EBV, and the recipient was negative for both EBV and CMV. His immunosuppressive regimen consisted of basiliximab for induction and MMF, tacrolimus, and steroids.

Four months after transplant, routine surveillance showed a PCR blood test that was positive for BKV at a titer of 73521 IU/mL, and there were decoy cells in urine. His creatinine increased from baseline level of 0.5 mg/dL to 1.1 mg/dL. The MMF was stopped, and leflunomide was initiated. The BK viral loads gradually decreased, and creatinine levels returned to baseline. At 3 months after treatment, 2 consecutive PCR blood tests were negative for BKV; therefore, leflunomide was stopped, and MMF was restarted. No adverse events of leflunomide treatment were recorded.

Case 3

A 13-year-old patient with renal dysplasia had previously received a preemptive renal transplant from a living related donor at the age of 11 years. The donor and the recipient both tested positive for CMV and EBV. At 3 months after transplant, on routine screening he was found to have BK viremia (6107 IU/mL) with a highest viral load of 31644 IU/mL and mildly increased creatinine from baseline of 0.8 mg/dL to 1 mg/dL. Decoy cells were detected in urine.

We stopped MMF and started leflunomide. After 3.5 months, 2 consecutive BKV PCR tests were negative, and MMF was restarted as leflunomide was stopped. Creatinine levels returned to baseline.

Case 4

An 11-year-old patient had steroid-resistant nephrotic syndrome due to a PLCE1 sequence variation. He had tested positive for CMV and EBV before he had received a living related renal transplant from a donor who had tested positive for CMV and EBV. During transplant, he had received rituximab and plasmapheresis to treat hypersen-sitization and our standard immunosuppression protocol with basiliximab, MMF, tacrolimus, and steroids.

At 5.5 months after transplant, he had a positive PCR result for blood BKV (2863 IU/mL). Blood BKV levels gradually increased to a highest viral load of 103657 IU/mL, and decoy cells were present in urine. At the same time, he developed neutropenia (N = 100); therefore, MMF was stopped. He received 2 doses of granulocyte-colony stimulating factor treatment, and neutropenia recovered; hence, leflunomide was initiated with regular full blood count monitoring, and there was no reoccurrence of neutropenia. Creatinine levels increased from baseline of 0.6 mg/dL to 0.8 mg/dL. At 3 months after treatment, results from a PCR blood test showed clearance of BK virus, and MMF was restarted. Creatinine levels returned to baseline.

All 4 patients during the follow-up period to the date of this writing have shown stable renal function and no reoccurrence of BKV infection.


A common complication of kidney transplant is BK viremia, especially in the first year after renal transplant. Indeed, all of our patients developed BKV infection in the first 6 months after transplant. Known risk factors for infection are young age of recipient and transplant from a deceased donor.10 However, in our study, 3 of 4 patients had received a living related transplant, and all 4 of them were older than 10 years. Two of our patients were hypersensitized and had received intensified immunosuppression before transplant with rituximab and plasmapheresis, and this treatment probably increased their risk for infection.

It is interesting to note that one of our patients presented with hemorrhagic cystitis. Although this presentation is common in patients after hemato-poietic stem cell transplant, it is unusual in renal transplant recipients. Very few adult cases have been reported in the literature so far,11-13 and regarding pediatric populations we could find only 1 case,14 a 13-year-old child who developed BKV-related hemorrhagic cystitis after transplant, which is similar to our case. Because of the limited number of cases, it is unknown whether patients who present with this rare complication have predisposing factors or different prognosis regarding the course of the infection.

There is presently no established recom-mendation for the treatment of BKV viremia and BKVN in children. In adults, the guidelines from the Kidney Disease: Improving Global Outcomes project5 recommend reduction of immunosup-pressive medications when BK plasma viral load is persistently greater than 10000 copies/mL. In addition, guidelines from the American Society of Transplantation Infectious Diseases Community of Practice15 recommend reduction of tacrolimus, reduction of the antiproliferative agent, and taper of corticosteroids to ≦10 mg/day, in patients with detectable BK viremia sustained >3 weeks. This strategy encounters the risk of rejection, especially in patients with increased rejection risk. Indeed, the North American Pediatric Renal Trials and Collaborative Studies Registry reported biopsy-proven rejection after immunosuppression reduction in 25% of patients.16

Several active BKV treatments have been used in small case series, including IVIG, mechanistic target of rapamycin inhibitors, ciprofloxacin, and leflunomide, but the benefits of these treatments have not been established. Although both the Kidney Disease: Improving Global Outcomes guidelines and the American Society of Transplantation Infectious Diseases Community of Practice guidelines do not suggest the use of any particular antiviral agent, there is wide heterogenicity on the management of BK nephropathy worldwide. A survey performed by the New England BK Consortium17 showed that, although all the respondents were aware of the uncertain benefits of additional agents, 61.5% of centers reported the use of leflunomide, 30.8% had used cidofovir, and 61.5% had considered using IVIG for persistent viremia or BKVN. On the other hand, an observational study in adults6 that compared the management of BKVN with immunosuppression reduction versus active treatment with a combination of leflunomide, IVIG, and ciprofloxacin concluded that the addition of these agents did not show any benefit on the long-term outcomes of patients with BKVN.

Of the proposed agents, leflunomide is a weak immunosuppressive drug that prevents lymphocyte expansion by inhibition of pyrimidine synthesis.18 Leflunomide has mainly been used in patients with rheumatoid arthritis; however, because of its antiviral properties, it has occasionally been used in patients with BKV infection. Some case series in adults have reported controversial results, and some others have shown a beneficial effect of leflunomide on BK viremia clearance without increasing the rejection risk.19

A systematic review8 of studies mainly in adult patients reported that a portion of the included studies showed promising results of BKVN treatment with leflunomide. However, due to the wide heterogenicity of the population and treatment protocols among different studies, the authors concluded that the role of leflunomide on BKVN remains unclear.

Recently, a multicenter retrospective study20 examined the effect of leflunomide on the treatment of BKVN in adult renal transplant recipients. In that study, leflunomide was introduced with a mean delay of 5.9 months after BK viremia diagnosis. Noting that pediatric patients were excluded, 76% of patients showed BK clearance in a mean period of 10.1 months after leflunomide commencement. These data are different from our experience, as we observed that all of our patients had complete BKV clearance much earlier, in a mean time of 3.3 months, and this might be attributed to the earlier initiation of the treatment and also the different cohort age.

There are very few pediatric case reports that have evaluated the role of leflunomide on BKV infection. Launay and colleagues21 have reported 7 patients with BK viremia treated with leflunomide along with immunosuppression reduction. They showed BKV clearance in 67% of their patients at various times after leflunomide initiation, from 1 to 31 months. In addition, Araya and colleagues22 have reported 3 patients for whom leflunomide was initiated many months after BKV diagnosis, following failure of initial treatment with cidofovir. These 3 patients had BKV clearance at 42, 12, and 5 months after beginning leflunomide. Our patients, for whom treatment was initiated immediately after diagnosis, showed a more rapid response as aforementioned, and it seems that early initiation of treatment might be a crucial factor that affects the period required for BKV clearance.

Our study had some limitations. First, we did not measure drug levels, because this test was not available in our unit. However, it is well known that data are scarce regarding the optimal drug levels in children, and results are difficult to interpret. Also, the effectiveness and toxicity of a drug can be assessed by measurement of BKV clearance and monitoring for toxicity with laboratory investigations, as we did. In all patients, we regularly monitored for associated toxic effects such as anemia, hepatitis, hemolysis, and thrombotic microangiopathy, and none of the patients showed any drug toxicity. An additional limitation is that we did not perform graft biopsies, because all of our patients showed a gradual decrease in creatinine levels after initiation of leflunomide therapy. Of note, the New England BK Consortium survey17 showed that 15.4% of participating centers intervened on patients with BKV infection by reduction of immunosuppression or initiation of leflunomide therapy without performing a biopsy, but it is widely accepted that a biopsy is mandatory for a persistent creatinine elevation, in order to differentiate between BKVN and rejection and, hence, to guide treatment.


Leflunomide can be a safe and effective treatment for BKV infection in children, especially if initiated early after BKV detection. We observed a rapid clearance of BKV in all of our patients and improvement of renal function without any adverse events. Although our observation must be confirmed by a randomized clinical trial, our experience shows very promising results of leflunomide as treatment for BKV infection in renal transplant recipients, which leads to reduced risk of BKVN and graft dysfunction.


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Volume : 21
Issue : 10
Pages : 826 - 830
DOI : 10.6002/ect.2023.0258

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From the 1 Pediatric Nephrology Department, P. and A. Kyriakou Children’s Hospital; and the 2Department of Nephrology and Kidney Transplantation, National and Kapodistrian University of Athens, Laiko General Hospital, Athens, Greece
Acknowledgements: The authors have not received any funding or grants in support of the presented research or for the preparation of this work and have no declarations of potential conflicts of interest.
Corresponding author: Evangelia Gole, Thivon and Levadeias str, Athens, Greece, 11527
Phone: +30 21 3 200 9343