Abhay Vats

Quantitative viral load monitoring and cidofovir therapy for the management of BK virus-associated nephropathy in children and adults.

Background. BK virus (BKV)-associated nephropathy (BKVAN) has been increasingly recognized as an important cause of renal transplant dysfunction. We report the role of quantitative viral load monitoring in the management of BKVAN. Methods. We developed a real-time quantitative polymerase chain reaction (PCR) assay for BKV detection in urine and plasma. Four renal allograft recipients, including two children, with BKVAN were treated with low-dose cidofovir and followed prospectively. Results. The PCR assay showed a detection limit of 10 viral copies with an intra-assay coefficient of variation of 19%. All four patients with BKVAN demonstrated intranuclear inclusions on allograft biopsy and a progressive rise in serum creatinine; three patients underwent multiple biopsies before the diagnosis of BKVAN was made. Three of the patients experienced a “viral syndrome” before the onset of renal dysfunction. One child also demonstrated an echogenic renal mass. All of the patients demonstrated strongly positive urinary PCR values (>100,000 copies/&mgr;L). BKV DNA was also detected in the plasma of three patients. All the patients were treated with intravenous low-dose cidofovir (0.25–1 mg/kg per dose, every 2–3 weeks, without probenecid). BK viruria resolved within 4 to 12 weeks (after 1–4 doses) of the cidofovir therapy, and all patients remain with stable renal function 6 to 26 months posttherapy. Conclusions. Quantitative PCR for BKV is a sensitive and reliable method for following the course of the infection in renal transplant patients. In addition, cidofovir therapy may be useful in the treatment of some of these patients, and its role needs to be investigated further.

Correlates of Quantitative Measurement of BK Polyomavirus (BKV) DNA with Clinical Course of BKV Infection in Renal Transplant Patients

ABSTRACT BK virus-allograft nephropathy (BKVAN) is an increasingly recognized complication after kidney transplantation. Quantitative tests have been advocated to monitor patients, but data demonstrating their efficacy are relatively limited. We developed a real-time PCR assay to quantitate BK virus loads in the setting of renal transplantation, and we correlated the BK virus load with clinical course and with the presence of BK virus in renal biopsy specimens. BK virus loads were measured in urine, plasma, and kidney biopsy samples in three clinical settings: (i) patients with asymptomatic BK viruria, (ii) patients with active BKVAN, and (iii) patients with resolved BKVAN. Active BKVAN was associated with BK viremia greater than 5 × 103 copies/ml and with BK viruria greater than 107 copies/ml in all cases. Resolution of nephropathy led to resolution of viremia, decreased viruria levels, and disappearance of viral inclusions, but low-level viral DNA persisted in biopsy specimens even for patients whose viruria was cleared. All but one patient in the resolved BKVAN group carried a urinary viral load below 107 copies/ml. Viral loads in patients with asymptomatic viruria were generally lower but in some cases overlapped with levels more typical of BKVAN. One patient with asymptomatic viruria and with a viral load overlapping values seen in BKVAN had developed nephropathy by the time of follow-up. In conclusion, serial measurement of viral loads by quantitative PCR is a useful tool in monitoring the course of BK virus infection. The results should be interpreted in conjunction with the clinical picture and biopsy findings.

Loop-Mediated Isothermal Amplification Assay for Rapid Detection of Common Strains of Escherichia coli

ABSTRACT We developed a highly sensitive and specific LAMP assay for Escherichia coli. It does not require DNA extraction and can detect as few as 10 copies. It detected all 36 of 36 E. coli isolates and all 22 urine samples (out of 89 samples tested) that had E. coli. This assay is rapid, low in cost, and simple to perform.

PRETRANSPLANT DIALYSIS STATUS AND OUTCOME OF RENAL TRANSPLANTATION IN NORTH AMERICAN CHILDREN: A NAPRTC STUDY. NORTH AMERICAN PEDIATRIC RENAL TRANSPLANT COOPERATIVE STUDY

BACKGROUND There are no large studies of the effect of pretransplant dialysis status on the outcome of renal transplantation (Tx) in children. This study evaluated the North American Pediatric Renal Transplant Cooperative Study (NAPRTCS) registry data for the outcome of Tx in pediatric patients who either (1) received their transplants preemptively or (2) were maintained on dialysis before receiving their transplants. METHODS We compared graft survival and patient survival rates, incidence of acute tubular necrosis (ATN), acute rejection episodes, and causes of graft failure in peritoneal dialysis (PD) patients with those maintained on hemodialysis (HD) and those undergoing preemptive Tx (PTx). RESULTS Primary Tx was performed in 2495 children (59% male; 61% Caucasian; 1090 PD, 780 HD, 625 PTx) between 1/1/1992 and 12/31/1996. The overall graft survival rates of the PD and HD groups were similar, but were less than that of the PTx group (3-year: 82% PD and HD, 89% PTx, overall P = 0.0003). Improved graft survival in the PTx group was present only in recipients of grafts from living donors. There was no difference in the overall patient survival rate at 3 years, or in time to first acute-rejection episodes in the three groups. The incidence of ATN in the first 7 days post-Tx was higher in PD and HD patients than in PTx patients (11% PD and 12% HD vs. 2% PTx, P<0.001; HD vs. PD, P = NS). The major single cause of graft failure in each group was: PD, vascular thrombosis (200%); HD, chronic rejection (27%); PTx, acute and chronic rejection (21% each). CONCLUSION NAPRTCS data show that graft survival is improved in patients receiving PTx, compared with those receiving PD and HD. Graft loss resulting from vascular thrombosis is more common in children who receive PD than in those receiving HD.

Effect of leflunomide and cidofovir on replication of BK virus in an in vitro culture system.

Background. Cidofovir and Leflunomide are used empirically in the treatment of BK virus nephropathy. The aim of this study is to quantify the antiviral activity of these drugs. Methods. BK virus was grown in a cell-culture system. The rate of viral replication in the presence or absence of the drug being tested was assessed using a quantitative polymerase chain reaction assay. Results. The inhibitory concentration, effective concentration, and selectivity index for Leflunomide are 39.7±6.9, 11.3±2.8, and 3.8±0.8 &mgr;g/mL, respectively. For Cidofovir, these indices were, respectively, 63.9±17.2, 36.3±11.7, and 2.3±0.8 &mgr;g/mL. Conclusions. The in vitro activity of Cidofovir and Leflunomide is modest, and the selectivity index is low. There is a need to develop more effective and less toxic anti-BK virus drugs for clinical use.

Quantitation of viral DNA in renal allograft tissue from patients with BK virus nephropathy.

Background. BK virus (BKV) allograft nephropathy (BKVAN) is a complication in renal transplantation recipients. Histopathology is the gold standard for diagnosis. Quantitative polymerase chain reaction (PCR) assay for renal biopsy has not been evaluated as a diagnostic test. Determination of renal BKV load may identify patients at risk for disease before histologic nephropathy. Methods. Quantitative PCR assay for BKV DNA was performed in 28 biopsies of patients with BKVAN; 50 biopsies were performed before a diagnosis of BKVAN, and 126 control biopsies were from patients without a history of BKVAN. Results. BKV DNA was present in 19 of 50 (38%) biopsies performed 1 to 164 weeks before diagnosis of BKVAN. The viral load (mean 216 copies/cell) was lower than in biopsies of patients with BKVAN (mean 6063 viral copies/cell, P <0.05). In 10 of 127 (7.8%) control biopsies, a low level of BKV DNA (mean 3.8 copies/cell) was found in three biopsies from chronic allograft nephropathy patients; two biopsies with acute rejection; four biopsies with borderline change; and one biopsy with cytomegalovirus nephritis. Conclusion. BKV load exceeding 59 copies per cell identified all cases of BKVAN. The diagnostic sensitivity, specificity, positive predictive value, and negative predictive value of quantitative PCR were 100%, 92.1%, 73.6%, and 100%, respectively. Lower levels of BKV DNA were identified in biopsies performed before viral nephropathy development. Future research will determine if earlier recognition of at-risk patients allows application of antiviral strategies to improve graft outcome.

Polyomavirus Allograft Nephropathy: Sequential Assessment of Histologic Viral Load, Tubulitis, and Graft Function Following Changes in Immunosuppression

Our initial cases of polyoma virus allograft nephropathy (PVAN) received pulse steroids due to anxiety about concomitant acute rejection triggered by the presence of tubulitis. However, our current policy is to reduce immunosuppression in all cases. The aim of this study was to determine whether clinical follow‐up in these patient categories shows any differences in: (a) histologic viral load, (b) grade of tubulitis, and (c) graft function. Reduced viral load assessed within 8 weeks was seen in 4/20 (20.0%) biopsies treated initially by increased immunosuppression, compared to 15/19 (83.3%) biopsies treated with reduced immunosuppression (p = 0.001, Fishers exact test). Yet, >70% reversal of the rise in serum creatinine occurred in only 3/19 (15.8%) and 1/19 (5.3%) patients, respectively, in these two groups. Improved tubulitis was seen in 11/20 (55%) of biopsies treated with steroids, despite the lack of beneficial effect on serum creatinine in 12/19 (63.1%) instances. In biopsies not treated with any change in immunosuppression, the serum creatinine remained stable in 1/5 (20%) and worsened in 4/5 (80%) biopsies. These data demonstrate that in biopsies with PVAN and tubulitis, reduced immunosuppression is more effective in lowering viral load than steroid therapy. Lack of parallelism between viral load, tubulitis grade, and serum creatinine illustrates a complex interplay of viral and alloimmune factors leading to graft injury.

DNA sequencing of viral capsid protein VP-1 region in patients with BK virus interstitial nephritis

Background. Mutations in the viral capsid protein VP-1 region are associated with increased pathogenicity of polyomavirus in experimental systems. This study sought to determine whether analogous viral genetic changes occur in human BK virus (BKV) interstitial nephritis (ISN). Methods. PCR was used to amplify a 94-bp nucleotide sequence of the viral capsid protein VP-1 region (positions 1740–1833, Dun numbering) in 49 biopsies obtained from 24 patients with BKV-ISN. DNA sequencing was performed by the dideoxy method. Result. The VP-1 region was highly polymorphic and 22 “hot spots” of sequence variability were noted. Genotypes I, II, and IV were assigned to 13, 1, and 5 cases, respectively, but 5 cases could not be unambiguously classified due to sequence heterogeneity at sites used to discriminate between genotypes. Even in cases where genotypes could be assigned, only 5 biopsies showed complete sequence identity with published genotype sequences. Sequential biopsies showed temporal changes in one or more nucleotides in all patients with multiple samples. In one patient, the initial biopsy showed viral genotype 1, although subsequent biopsies showed complex genetic patterns, including a biopsy consistent with viral genotype IV. Conclusions. Many viral strains associated with BKV-ISN are difficult to classify and possibly distinct from those described in kidney transplant recipients without BKV-ISN. VP-1 sequences undergo continual modification as patients are followed in time. This genetic instability could conceivably have implications for evasion of host immunity and development of resistance to antiviral drugs.

Update of PAX2 mutations in renal coloboma syndrome and establishment of a locus-specific database

Renal coloboma syndrome, also known as papillorenal syndrome is an autosomal‐dominant disorder characterized by ocular and renal malformations. Mutations in the paired‐box gene, PAX2, have been identified in approximately half of individuals with classic findings of renal hypoplasia/dysplasia and abnormalities of the optic nerve. Prior to 2011, there was no actively maintained locus‐specific database (LSDB) cataloguing the extent of genetic variation in the PAX2 gene and phenotypic variation in individuals with renal coloboma syndrome. Review of published cases and the collective diagnostic experience of three laboratories in the United States, France, and New Zealand identified 55 unique mutations in 173 individuals from 86 families. The three clinical laboratories participating in this collaboration contributed 28 novel variations in 68 individuals in 33 families, which represent a 50% increase in the number of variations, patients, and families published in the medical literature. An LSDB was created using the Leiden Open Variation Database platform: www.lovd.nl/PAX2. The most common findings reported in this series were abnormal renal structure or function (92% of individuals), ophthalmological abnormalities (77% of individuals), and hearing loss (7% of individuals). Additional clinical findings and genetic counseling implications are discussed. Hum Mutat 33:457–466, 2012.

Long-term antiproteinuric and renoprotective efficacy and safety of losartan in children with proteinuria

BACKGROUND Angiotensin receptor antagonists are effective in reducing proteinuria by an action independent of blood pressure. As a consequence, such agents retard progressive renal dysfunction in adults with chronic proteinuria. Long-term efficacy and tolerability data in children are unavailable. METHODS Efficacy of losartan in reducing proteinuria and in preserving renal function was prospectively assessed in 52 consecutive children under 18 years of age with chronic proteinuric renal disorders, an initial creatinine clearance > or =25 mL/min/1.73 m(2), and a minimum of two or more follow-up visits. Thirty had proteinuria (P), and 22 had proteinuria combined with hypertension (P+H). Adverse effects were also evaluated. RESULTS Proteinuria had persisted or increased during a mean interval of 8.5 months before initiation of losartan at a mean dosage of 0.8 mg/kg/d. Mean protein excretion before starting losartan was 2453 mg/m(2)/d and fell by 34% at a mean follow-up time of six weeks (visit I, P<.05), and between 64% and 67% at mean follow-up periods of 0.38, 0.71, and 2.48 years corresponding to visits II, III, and IV (all P<.001 compared with baseline). The proportion of children with protein excretion exceeding 40 mg/m(2)/h (nephrotic range proteinuria) or nephrotic syndrome (>3500 mg/1.73 m(2)/d) fell from 42% and 40% at the start, to 24% and 8%, respectively, at visit IV (P<.01). Mean creatinine clearance as well as serum potassium and total CO(2) levels remained unchanged during the time of follow-up. Reduction in proteinuria in the P subgroup alone correlated with lowering in diastolic blood pressure at visit II and with both diastolic and systolic blood pressure at visits III and IV (all P<.05); it was largely independent of reduction in blood pressure in the P+H subgroup. The concomitant use of immunosuppressive agents in 28 of the 52 children had an influence on proteinuria only at baseline and at visit I (P<.05). There was no significant change in height or body mass index Z scores. Thirteen children had adverse effects potentially ascribed to losartan; most of these either improved or resolved with dosage adjustment or resulted in its discontinuation in 9 of the 52 children (17%). CONCLUSION Losartan therapy was associated with a marked and sustained reduction in proteinuria and in preservation of GFR in children with chronic proteinuric disorders. The association between proteinuria and systemic blood pressure reduction was complex: it was largely limited to the first year of losartan therapy and was more pronounced in the normotensive subgroup. Losartan was generally well tolerated.