Mutations in the BC‐loop of the BKV VP1 region do not influence viral load in renal transplant patients

Abstract

The reactivation and replication of the BK polyomavirus (BKV) leading to BKV-associated nephropathy (BKVAN) is one of the major complications in renal transplantation patients. BKV isolates were classified into four subtypes (I-IV) based on genotype variations within the VP1-coding region. The type-specific amino acid differences cluster within the BC-loop of the major capsid protein VP1. As demonstrated in vitro, mutations in this region also play a role in the infectivity, attachment and stability of viral particles. Therefore, we analyzed the prevalence of BC-loop mutations in isolates of kidney transplant patients and compared their viral load in the urine. The VP1 subtyping regions of BKV isolates obtained from urine samples of 45 renal transplant patients were sequenced. The phylogenetic analysis of these sequences revealed that subtype I (66.67%) is the most prevalent genotype. The remaining isolates belong to subtype IV (33.33%). A high frequency of changes to specific amino acids within the BC-loop was identified among the BKV isolates from renal transplant patients. Patients with BKVAN exhibited a higher viral replication than patients without nephropathy. Although titers of isolates of subtype I were higher than titers of subtype IV isolates, the difference did not reach statistical significance. In addition, amino acid changes in the BC-loop did not influence the viral load and the incidence of BKVAN. These in vivo results demonstrate that high replication rates which serve as a predictive marker for BKVAN are not caused by altered receptor binding or affinity via mutated BC-loops.

BK virus‐associated infection in cerebrospinal fluid of neurological patients and mutation analysis of the complete VP1 gene in different patient groups

“…In a recent study, mutations in the BC-loop of BKV isolates obtained from urine samples of 45 kidney transplant patients were determined (Krautkramer et al, 2009). Two of the mutations (E82D and H139N) reported by these authors were also identified in this study in RTR17 and RTR26, in a BKV isolate in the CSF of one neurological patient (NP4) and in two out of six of our bone marrow transplant patients (BMT31 and BMT32).…”

“…This is exemplified by BKV variants 1, 4, and 11 which were present in several patient groups. A lack of such correlation has earlier been reported in nephropathy and SLE patients (Jin et al, 1995;Bendiksen et al, 2000a;Baksh et al, 2001;Randhawa et al, 2002;Boldorini et al, 2009;Krautkramer et al, 2009;Tremolada et al, 2010a,b). Identical strains (variants 1, 4, and 11) were detected in different patient groups, suggesting that a particular BKV strain is not associated with a specific disease.…”

“…Consequently, BKV subtypes distribution has been evaluated in different groups of immunosuppressed patients such as renal transplant recipients, bone marrow transplant patients, stem cell transplant recipients, AIDS patients, systemic lupus erythematosus (SLE) patients, and pregnant women (Jin et al, 1995; Krumbholz et al, 2006;Gosert et al, 2008;Boldorini et al, 2009;Krautkramer et al, 2009;Tremolada et al, 2010a,b). In addition, the clinical involvement of BKV VP1 amino acid substitutions in the subtyping region has been assessed in patients with PVAN and SLE patients (Bendiksen et al, 2000a;Randhawa et al, 2002;Boldorini et al, 2009;Krautkramer et al, 2009;Tremolada et al, 2010a,b). However, in none of these studies, a specific subtype or pattern of mutations in VP1 was essential for the development of BKV-associated pathology.…”

Limited Variation in BK Virus T-Cell Epitopes Revealed by Next-Generation Sequencing

“…In one study, single base-pair mutations were detected more frequently in samples from patients with BK nephropathy, but amino acid changes were randomly distributed in BK nephropathy patients and controls (28). Other studies have identified amino acid changes in the external loops of VP1, which mediate BKV attachment to target cells but did not find an association with viral load or incidence of BK nephropathy (29,30). Similarly, amplifications, deletions, and rearrangements in the NCCR have not been shown to influence the development of hemorrhagic cystitis or BK nephropathy in either HCT or kidney transplant recipients (27,31).…”

A rapid and efficient method BK polyomavirus genotyping by high‐resolution melting analysis

“…It is this genomic diversity that is responsible for discrepancies in the research on the clinical relevance of BKV and its associations with BKVN. For example, whereas Krautkramer et al [2009] found no correlation between mutations in BKV VP1 genes and BKV viral load, Boldorini et al [2009b] identified a correlation between BKVN and the frequency of single base-pair mutations in BKV DNA. On the other hand, Chan et al [2009] described observing a case of BKVN in which a BKV large-T antigen was unreactive.…”