Polyoma virus in pediatric renal transplantation

A novel treatment regimen for BK viremia

BACKGROUND

BK viremia, a prerequisite for BK virus nephropathy (BKVN), affects 5% to 16% of pediatric renal transplant recipients (PRTR). We evaluated the safety and efficacy of a novel approach to treating BK viremia using fluoroquinolones and leflunomide in PRTR.

METHODS

We studied 230 PRTR at Mattel Children's Hospital, UCLA, who underwent renal transplantation between January 2003 and October 2010. Nineteen patients were found to have BK viremia. Ciprofloxacin was started when the BK viral load was greater than 625 copies/mL, and patients were switched to leflunomide if BK viral load did not decrease after 2 months of ciprofloxacin therapy. All patients underwent transplant kidney biopsy, and their estimated glomerular filtration rate (eGFR) and BK PCR was measured serially. The side effects of ciprofloxacin and leflunomide were recorded in each patient.

RESULTS

There was a significant decrease in BK viral load in patients treated with ciprofloxacin and leflunomide (P<0.001) with only a small reduction in immunosuppression. BK viremia was associated with a significantly decreased eGFR (P<0.001), and treatment with ciprofloxacin and leflunomide was associated with improved eGFR (P<0.001). This approach resulted in a BKVN rate of only 1%.

CONCLUSIONS

This analysis demonstrates for the first time that, used in a stepwise fashion, ciprofloxacin and leflunomide are effective and safe treatments for BK viremia in PRTR.

Polyomavirus BK: possibly associated skin eruption in a patient with hemorrhagic cystitis

A 14-year-old girl with Fanconi anemia was submitted to allogeneic hematopoietic stem cell transplantation. After 17 days she developed hemorrhagic cystitis due to polyoma BK virus (BKV), confirmed by PCR (polymerase chain reaction). Two weeks after the appearance of the urinary symptoms the patient presented numerous papules and vesicles on both hands and feet. PCR of the skin lesions and plasma was positive for BKV. The relationship of BKV with frequent infections in immunocompromised patients is well established. The positive PCR of vesicular fluid suggests that this was the causative agent of the skin lesion in this case. There are no reports of skin lesions with positive PCR for BKV.

Treatment strategies to minimize or prevent chronic allograft dysfunction in pediatric renal transplant recipients: an overview

Long-term allograft survival poses a major problem in pediatric renal transplantation, with allograft nephropathy being the principal cause of graft failure after the first post-transplant year. The mechanisms of nephron loss resulting in graft dysfunction are multiple, comprising both immunologic factors such as acute and chronic antibody- or T-cell-mediated rejection and non-immunologic components. The latter include peri-transplant injuries and renovascular lesions (renal artery stenosis, thrombosis) as well as cardiovascular risk factors such as arterial hypertension and hyperlipidemia. Another relevant issue leading to progressive nephron loss and declining kidney transplant function is acute and chronic nephrotoxicity induced by the calcineurin inhibitors (CNIs) ciclosporin (cyclosporine microemulsion) and tacrolimus. Furthermore, the presence of an abnormal lower urinary tract as well as bacterial (recurrent pyelonephritis) and viral (cytomegalovirus [CMV], polyomavirus [BK virus; BKV]) infections are crucial factors involved in the incidence of chronic allograft dysfunction and graft failure. Renovascular lesions and lower urinary tract obstruction are typical indicators for surgical intervention. The aim of treatment in pediatric patients with renal failure secondary to a dysfunctional lower urinary tract is to create a sterile, continent, and nonrefluxive reservoir. Surgical techniques such as bladder augmentation and the introduction of intermittent catheterization and anticholinergic therapy have significantly improved graft outcome. Arterial hypertension, another factor responsible for graft function deterioration in pediatric renal transplant recipients, is controlled preferably by the use of angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor antagonists, which are known to possess nephroprotective properties in addition to their potent antihypertensive effects. Although treatment of subclinical rejection with augmented immunosuppression has been associated with better graft survival, an increase of the immunosuppressive level to avoid subclinical rejection should be weighed against the risk of infection. The majority of viral infections affecting kidney allografts are caused by CMV and BKV. Antiviral CMV prophylaxis or pre-emptive therapy with ganciclovir has been shown to have beneficial effects in the pediatric renal transplant population. Treatment of BKV-induced nephropathy is based on reduction of the immunosuppressant therapy, although specific antiviral agents such as cidofovir and leflunomide are known to inhibit BKV. However, cidofovir itself is nephrotoxic and should therefore be administered cautiously to pediatric renal transplant patients. Since CNIs are likewise known for their nephrotoxic effects, especially with long-term use, alteration of the immunosuppressant regimen is necessary in case of deteriorating graft function due to CNI-induced histopathologic changes. Complete CNI avoidance seems inappropriate because, in this situation in pediatric renal transplant recipients, other relatively potent immunosuppressant agents such as lymphocyte-depleting antibodies, which are frequently accompanied by a higher incidence of infections, are needed for rejection prophylaxis. CNI withdrawal and switching of the immunosuppressant regimen from CNI therapy to sirolimus may be an option for some pediatric renal transplant patients with less advanced graft function deterioration. Nevertheless, potential adverse events such as aggravation of proteinuria, hyperlipidemia, myelosuppression, and hypergonadotropic hypogonadism have to be considered, and controlled studies are lacking. At present, an immunosuppressant maintenance therapy composed of low-dose tacrolimus or ciclosporin (CNI minimization) and mycophenolate mofetil with low-dose corticosteroids appears to be the most promising strategy to adopt in pediatric renal transplant recipients at low or normal immunologic risk.

Antibody responses to recombinant polyomavirus BK large T and VP1 proteins in young kidney transplant patients

BK virus (BKV)-specific immunity is critical for polyomavirus-associated nephropathy, but antibody responses are incompletely defined. We compared the hemagglutination inhibition assay (HIA) with immunoglobulin G enzyme immunoassays (EIA) to BKV proteins expressed in baculovirus-infected insect cells. N-terminal, internal, and C-terminal domains of the BKV large T antigen (BKLT) were fused to glutathione S-transferase (GST), yielding GST-BKLTD1, GST-BKLTD2, and GST-BKLTD3, respectively. The BKV capsid VP1 was expressed as a GST fusion (BKVP1) or as a native VP1 assembled into viruslike particles (BKVLP). We tested 422 sera from 28 healthy donors (HD), 99 dialysis patients (DP; median age, 15 years; range, 3 to 32 years), and 46 age-matched kidney transplant patients (KTP; median age, 15 years; range, 2 to 33 years). In HD, HIA and BKVLP EIA both yielded a 91.7% seroreactivity, whereas all other EIA responses were lower (BKVP1, 83.3%; BKLTD1, 25%; BKLTD2, 29%; BKLTD3, 40%). HIA titers significantly correlated with EIA levels for BKVLP, BKVP1, and BKLTD1 but not for BKLTD2 or BKLTD3, which were barely above the cutoff. In DP, the seroreactivities of HIA, BKVLP, and BKLTD1 were lower than that in HD (63.6%, 86.9%, and 10.1%, respectively) and they had lower titers (P < 0.001). In KTP, seropositivities for BKVLP, BKVP1, and BKLTD1 were 78%, 50%, and 17%, respectively, but anti-BKVLP levels increased significantly in KTP with viruria and viremia, whereas anti-BKLTD1 levels increased after clearing sustained BKV viremia. In conclusion, anti-BKVLP is equivalent to HIA in HD but is more sensitive to determine the BKV serostatus in DP and KTP. In KTP, anti-BKVLP responds to recent BKV viruria and viremia, whereas anti-BKLTD1 may indicate emerging BKV-specific immune control.

Calcineurin inhibitor sparing in paediatric solid organ transplantation : managing the efficacy/toxicity conundrum

Despite their efficacy, the calcineurin inhibitors (CNIs) ciclosporin and tacrolimus carry a risk of debilitating adverse effects, especially nephrotoxicity, that affect the long-term outcome and survival of children who are given organ transplants. Simple reduction in dosage of CNI has little or no long-term benefit on their adverse effects, and complete withdrawal without threatening graft outcome may only be possible after liver transplantation. Until the last decade, the only option was to increase corticosteroid and/or azathioprine doses, which imposed additional long-term hazards. Considered here are the emerging generation of new agents offering an opportunity for improving long-term graft survival, minimizing CNI-related adverse events and ensuring patient well-being.A holistic, multifaceted strategy may need to be considered - initial selection and optimized use and monitoring of immunosuppressant regimens, early recognition of indicators of patient and graft dysfunction, and, where applicable, early introduction of CNI-sparing regimens facilitating CNI withdrawal. The evidence reviewed here supports these approaches but remains far from definitive in paediatric solid organ transplantation. Because de novo immunosuppression uses CNI in more than 93% of patients, reduction of CNI-related adverse effects has focused on CNI sparing or withdrawal.A recurring theme where sirolimus and mycophenolate mofetil have been used for this purpose is the importance of their early introduction to limit CNI damage and provide long-term benefit: for example, long-term renal function critically reflects that at 1 year post-transplant. While mycophenolic acid shows advantages over sirolimus in preserving renal function because the latter is associated with proteinuria, sirolimus appears the more potent immunosuppressant but also impairs early wound healing. The use of CNI-free immunosuppressant regimens with depleting or non-depleting antibodies plus sirolimus and mycophenolic acid needs much wider investigation to achieve acceptable rejection rates and conserve renal function. The adverse effects of the alternative immunosuppressants, particularly the dyslipidaemia associated with sirolimus, needs to be minimized to avoid replacing one set of adverse effects (from CNIs) with another. While we can only conjecture that judicious combinations with the second generation of novel immunosuppressants currently in development will provide these solutions, a rationale of low-dose therapy with multiple immunosuppressants acting by complementary mechanisms seems to hold the promise for efficacy with minimal toxicity until the vision of tolerance achieves reality.

Kidney transplantation in children and adolescents

Worldwide, specific pediatric allocation schemes successfully try to minimize waiting time for children with end-stage renal disease (ESRD). The article is a review of current issues in pediatric kidney transplantation. The procedure is the treatment of choice for children and adolescents with ESRD, with 1- and 3-year graft survival rates of 95% and 90% and recipient survival after 5 and 10 years of 95% and 90%. Preoperative surgery is often necessary to minimize negative effects of congenital anomalies. No minimum age exists for pediatric transplantation, but most often the recipient body weight is ideally above 10 to 15 kg. Technical concepts should include extravesical anastomosis, stenting of the ureter, and potentially intraperitoneal placement of the graft. Immunosuppression has constantly improved. The aim is a tailored regimen to reduce side effects and improve compliance, which necessitates intense counseling of the child and the parents prior to, during, and after transplantation as many adolescents lose their graft due to noncompliance. Intense follow-up must also exclude infections, especially with herpes and polyoma viruses. For the future, age matching may be only one promising concept to improve results. As only a small number of children require the procedure in each country, multinational studies should be initiated to optimize outcomes in children and adolescents.

BK virus infection, replication, and diseases in pediatric kidney transplantation

Polyomavirus-associated nephropathy is diagnosed in 2-8% of pediatric renal transplants and often precedes renal allograft dysfunction. Without intervention, however, significant graft dysfunction is observed in more than 50% of cases, although progressive early graft loss is reported in only three of 32 (9%) of cases. No specific treatment is available, but early decrease in immunosuppression is followed by declining human polyomavirus type 1 (BK virus) replication and improved outcome. The data suggest differences between pediatric and adult kidney transplantation. Possibly, pediatric patients might be able to mount a more vigorous BK virus-specific immune response than adult patients under similar modulation of immunosuppression. Also the role of cidofovir and leflunomide is still unresolved in pediatric patients. Larger prospective trials are needed to better define the impact of BK virus immunity for replication and disease as well as the role of reducing immunosuppression with or without cidofovir or leflunomide in pediatric transplant patients.