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.
The emerging role of humoral immunity in the pathogenesis of chronic allograft damage has prompted research aimed at assessing the role of anti‐HLA antibody (Ab) monitoring as a tool to predict ...allograft outcome. Data on the natural history of allografts in children developing de novo Ab after transplantation are limited. Utilizing sera collected pretransplant, and serially posttransplant, we retrospectively evaluated 82 consecutive primary pediatric kidney recipients, without pretransplant donor‐specific antibodies (DSA), for de novo Ab occurrence, and compared results with clinical–pathologic data. At 4.3‐year follow up, 19 patients (23%) developed de novo DSA whereas 24 had de novo non‐DSA (NDSA, 29%). DSA appeared at a median time of 24 months after transplantation and were mostly directed to HLA‐DQ antigens. Among the 82 patients, eight developed late/chronic active C4d+ antibody‐mediated rejection (AMR), and four C4d‐negative AMR. Late AMR correlated with DSA (p < 0.01), whose development preceded AMR by 1‐year median time. Patients with DSA had a median serum creatinine of 1.44 mg/dL at follow up, significantly higher than NDSA and Ab‐negative patients (p < 0.005). In our pediatric cohort, DSA identify patients at risk of renal dysfunction, AMR and graft loss; treatment started at Ab emergence might prevent AMR occurrence and/or progression to graft failure.
This study of de novo anti‐HLA antibody monitoring in pediatric kidney recipients demonstrates an increased incidence of late humoral rejection and poorer outcome in patients developing donor‐specific antibodies.
Alloantibody‐mediated graft injury is a major cause of kidney dysfunction and loss. The complement‐binding ability of de novo donor‐specific antibodies (dnDSAs) has been suggested as a prognostic ...tool to stratify patients for clinical risk. In this study, we analyzed posttransplant kinetics of complement‐fixing dnDSAs and their role in antibody‐mediated rejection development and graft loss. A total of 114 pediatric nonsensitized recipients of first kidney allograft were periodically monitored for dnDSAs using flow bead assays, followed by C3d and C1q assay in case of positivity. Overall, 39 patients developed dnDSAs, which were C1q+ and C3d+ in 25 and nine patients, respectively. At follow‐up, progressive acquisition over time of dnDSA C1q and C3d binding ability, within the same antigenic specificity, was observed, paralleled by an increase in mean fluorescence intensity that correlated with clinical outcome. C3d‐fixing dnDSAs were better fit to stratify graft loss risk when the different dnDSA categories were evaluated in combined models because the 10‐year graft survival probability was lower in patients with C3d‐binding dnDSA than in those without dnDSAs or with C1q+/C3d− or non‐complement‐binding dnDSAs (40% vs. 94%, 100%, and 100%, respectively). Based on the kinetics profile, we favor dnDSA removal or modulation at first confirmed positivity, with treatment intensification guided by dnDSA biological characteristics.
In this longitudinal study of renal transplant recipients, the authors demonstrate that patients with de novo donor‐specific HLA antibodies capable of C3d binding are more likely to develop antibody‐mediated rejection and graft loss, and describe the dynamic and progressive phenomenon of complement‐binding ability acquisition.
Polyoma BK virus (BKV)‐associated nephropathy (PVAN) is a relevant cause of poor renal allograft survival. In a prospective analysis, we monitored BKV DNA in blood and urine samples from 62 ...consecutive pediatric kidney recipients. In patients with BKV replication, we analyzed the impact of reduction of maintenance immunosuppression on viral load kinetics and PVAN in patients with BKV replication. BKV‐specific immunity was concomitantly evaluated on blood samples of viremic patients, by measuring the frequency of BKV‐specific interferon‐γ‐producing and cytotoxic T cells, and BKV IgG antibody levels. At a median follow‐up of 24 months, BK viruria was observed in 39 of 62 patients, while BK viremia developed in 13 patients (21%). In all viremic patients, immunosuppression reduction resulted in the clearance of viremia, and prevented development of PVAN, without increasing the rate of acute rejection or causing graft dysfunction. As a consequence of immunosuppression adjustment, an expansion of BKV‐specific cellular immunity was observed that coincided with viral clearance. We conclude that treating pediatric kidney transplant patients pre‐emptively with immunosuppression reduction guided by BKV DNA in blood is safe and effective to prevent onset of PVAN. BKV‐specific cellular immunity may be useful to guide this intervention.
This prospective study conducted in 62 pediatric kidney transplant recipients shows that pre‐emptive reduction of immunosuppression in patients with BKV reactivation allows for viral clearance and prevention of BKV‐associated nephropathy through reconstitution of virus specific immunity, without increased incidence of acute rejection.
Fast BK virus (BKV) replication in renal tubular epithelial cells drives polyomavirus‐BK‐associated nephropathy (PVAN) to premature kidney transplant (KT) failure. BKV also replicates in urothelial ...cells, but remains asymptomatic in two‐thirds of affected KT patients. Comparing 518 day‐matched plasma‐urine samples from 223 KT patients, BKV loads were ∼3000‐fold higher in urine than in plasma (p < 0.000001). Molecular and quantitative parameters indicated that >95% of urine BKV loads resulted from urothelial replication and <5% from tubular epithelial replication. Fast BKV replication dynamics in plasma and urine with half‐lives of <12 h accounted for daily urothelial and tubular epithelial cell loss of 4×107 and 6×107, respectively. BKV dynamics in both sites were only partly linked, with full and partial discordance in 36% and 32%, respectively. Viral expansion was best explained by models where BKV replication started in the kidney followed by urothelial amplification and tubular epithelial cell cross‐feeding reaching a dynamic equilibrium after ∼10 weeks. Curtailing intrarenal replication by 50% was ineffective and >80% was required for clearing viremia within 7 weeks, but viruria persisted for >14 weeks. Reductions >90% cleared viremia and viruria by 3 and 10 weeks, respectively. The model was clinically validated in prospectively monitored KT patients supporting >80% curtailing for optimal interventions.
Assessment of BK virus loads in urine and plasma provides novel insights into the importance of replication in renal tubular epithelium as opposed to urothelial cells, and of the importance of curtailing replication in kidney cells in terminating viremia.
: The human polyomavirus type 1, also called BK virus (BKV), causes polyomavirus‐associated nephropathy (PVAN) in 1–10% of renal transplant recipients, with graft loss in over 50% of cases. The risk ...factors for PVAN are not conclusively defined and likely involve complementing determinants of recipient, graft, and virus. A central element seems to be the failing balance between BKV replication and BKV‐specific immune control, which can result from intense triple immunosuppression, HLA‐mismatches, prior rejection and anti‐rejection treatment, or BKV‐seropositive donor/seronegative recipient pairs. Consistent with this general hypothesis, the timely reduction of immunosuppression in kidney transplant recipients reduced graft loss to less than 10% of cases. However, the BKV‐specific humoral and cellular immune response is not well characterized. Recent work from several groups suggest that changes in antibody titers and BKV‐specific CD4+ and CD8+ T cells may help to better define the risk and the course of PVAN in renal transplant patients.
Donor‐specific HLA antibody (DSA)‐mediated graft injury is the major cause of kidney loss. Among DSA characteristics, graft homing has been suggested as an indicator of severe tissue damage. We ...analyzed the role of de novo DSA (dnDSA) graft homing on kidney transplantation outcome. Graft biopsy specimens and parallel sera from 48 nonsensitized pediatric kidney recipients were analyzed. Serum samples and eluates from graft biopsy specimens were tested for the presence of dnDSAs with flow bead technology. Intragraft dnDSAs (gDSAs) were never detected in the absence of serum dnDSAs (sDSAs), whereas in the presence of sDSAs, gDSAs were demonstrated in 72% of biopsy specimens. A significantly higher homing capability was expressed by class II sDSAs endowed with high mean fluorescence intensity and C3d‐ and/or C1q‐fixing properties. In patients with available sequential biopsy specimens, we detected gDSAs before the appearance of antibody‐mediated rejection. In sDSA‐positive patients, gDSA positivity did not allow stratification for antibody‐mediated graft lesions and graft loss. However, a consistent detection of skewed unique DSA specificities was observed over time within the graft, likely responsible for the damage. Our results indicate that gDSAs could represent an instrumental tool to identify, among sDSAs, clinically relevant antibody specificities requiring monitoring and possibly guiding patient management.
This systematic evaluation of de novo donor‐specific HLA antibodies in kidney biopsies and parallel sera collected longitudinally from a pediatric kidney transplant cohort demonstrates that intragraft donor‐specific antibodies appear before development of antibody‐mediated histological lesions, and, over time, maintain a consistently skewed antibody pattern when compared to the circulating specificity profile.
Although a growing body of literature regarding polyoma BK virus (BKV) infection and associated interstitial nephritis in kidney-allograft recipients is becoming available, the impact of BKV ...infection in the pediatric population has not been fully evaluated.
In a retrospective analysis, we performed polymerase chain reaction (PCR) assays for BKV DNA in serum and urine samples from 100 pediatric kidney-allograft recipients referred to our institution in the last 5 years.
BKV viruria was observed in 26 of 100 patients, whereas BKV viremia was demonstrated in 5 patients. Serum creatinine was significantly higher in recipients with positive BK viremia compared with BKV DNA-negative patients (mean 2.66 vs. 1.14 mg/100 mL). Renal biopsy performed in 3 of 5 patients showed graft damage consistent with interstitial nephropathy. In the univariate analysis, negative antibody status of the recipient and the presence of mycophenolate mofetil in baseline immunosuppression were the two factors predictive of active BKV infection.
Our study shows that BKV-associated nephropathy is a relevant complication in the pediatric kidney transplantation setting also. Identification of patients at risk of developing virus-associated nephropathy, through prospective quantification of viral load, could improve clinical outcome by allowing the use of timely preemptive therapy guided by BKV DNA levels.
Podocin mutations (NPHS2 gene) are responsible for the autosomal recessive form of steroid-resistant nephrotic syndrome. As a result of a screening for these gene alterations in a cohort of Italian ...patients with nonfamilial nephrotic syndrome and histologic focal segmental glomerulosclerosis (FSGS), nine patients with NPHS2 gene homozygous or composite heterozygous mutations were found. In addition to the previously described defects, two novel mutations at exon 4 were identified (frameshift, L169P); four single nucleotide polymorphisms (SNPs) and one dinucleotide repeat were also identified. On the basis of haplotype analysis, a founder effect was suggested for the 419delG mutation, the most frequently observed in the patients studied. Patients carrying NPHS2 mutations and without a family history of nephrotic syndrome were indistinguishable from those with idiopathic FSGS on the basis of the clinical phenotype. Two of the nine patients had normal renal function at 3 and 10 yr of age, despite the presence of the nephrotic syndrome. The other seven had reached end-stage renal failure at a mean age of 9.6 yr (range, 4 to 17 yr) and had received renal allografts. In those presenting with end-stage renal failure, the clinical and laboratory features both before and after transplantation were similar, including the age at onset, the amount of proteinuria, and the absence of any response to steroids and other immunosuppressants. Finally, two children presented recurrence of mild proteinuria after transplantation, which promptly remitted after plasmapheresis combined with cyclophosphamide. These data demonstrate that podocin mutations in nonfamilial cases of steroid-resistant nephrotic syndrome are frequent and may be due in one case to a founder effect. The pretransplantation and posttransplantation outcomes in the group of patients with mutations of the podocin gene are similar to classical idiopathic FSGS, including the possibility of recurrence of proteinuria that is mild and responsive to plasmapheresis. These observations support a role of molecular screening of the podocin gene in patients with nephrotic syndrome before immunosuppressive treatment is started.
The recurrence of focal segmental glomerulosclerosis (FSGS) after renal transplantation has a potentially detrimental course toward the loss of renal function. To identify prognostic markers for ...recurrence and efficacy of treatment, we evaluated the outcome of 32 renal allografts in 29 pediatric patients with FSGS who underwent transplantation from 1987 to 1998 in the North Italy Transplant program. Recurrence was observed in 15 of 29 patients (52%) after the first transplant and in 3 of 3 patients (100%) after the second graft. No significant differences in sex, age at FSGS onset, age at transplantation, or length of dialysis were noted between patients with recurrent and nonrecurrent FSGS. Those with recurrence originally developed end-stage renal failure faster (3.9 years) than those without recurrence (6.2 years). Pretransplantation serum samples from 25 patients were tested in an in vitro assay that evaluates glomerular permeability to albumin. FSGS recurred in 11 of 13 children who tested positive for the permeability factor and in 4 of 12 patients with a negative test result; the odds ratio for developing recurrence was 10.99 (95% confidence limit, 1.6 to 75.47) in the former group. The immediate onset of proteinuria after transplantation was a negative prognostic factor for the outcome; 6 of 9 patients in whom proteinuria appeared within 2 days of transplantation returned to dialysis in less than 24 months. In 9 of 11 patients who were treated with plasmapheresis plus cyclophosphamide after recurrence, proteinuria was successfully reversed and persistent remission was obtained in 7 patients. These data show that the glomerular permeability test has a significant predictive value for the recurrence of proteinuria in children with FSGS who have received a renal allograft. Of the clinical parameters considered, only the duration of disease was significantly different in patients with recurrent versus nonrecurrent FSGS. Treatment with plasmapheresis plus cyclophosphamide can be effective in the control of FSGS relapse after renal transplantation.
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