Molecular Characterization of BK Polyomavirus Replication in Allogeneic Hematopoietic Cell Transplantation.

BACKGROUND: High-level BK polyomavirus (BKPyV) replication in allogeneic hematopoietic cell transplantation (HCT) predicts failing immune control and BKPyV-associated hemorrhagic cystitis (BKPyV-HC).

METHODS: To identify molecular markers of BKPyV-replication and disease, we scrutinized BKPyV-DNA loads in longitudinal urine and plasma pairs from 20 HCT-patients using quantitative nucleic-acid-testing (QNAT), DNase-I treatment prior to QNAT, next-generation-sequencing (NGS) and tested cell-mediated immunity.

RESULTS: We found that larger QNAT amplicons led to under-quantification and false-negatives results (p < 0.001). DNase-I reduced urine and plasma BKPyV-loads by >90% (p < 0.001) indicating non-encapsidated BKPyV-genomes. DNase-resistant urine BKPyV-loads remained infectious in cell culture. BKPyV-genome fragmentation of ≤250 bp impaired NGS-coverage of genetic variation using 1000 bp and 5000 bp targets. Conversely, 250bp-amplicons captured viral minority variants. We identified genotype-specific and genotype-independent changes in capsid-Vp1 or large T-antigen predicted to escape from antibody neutralization or HLA-presentation to CD8 T-cells, respectively. Genotype-specific changes in immunodominant 9mers were associated with reduced or absent CD8 T-cell responses. Thus, failure to control BKPyV-replication in HCT-patients may involve insufficient genotype-specific cytotoxic CD8 T-cell responses potentially predictable by low neutralizing antibodies as well as genotype-independent immune escape of variants.

CONCLUSION: Our results provide new insights for patient evaluation and for designing immune protection through neutralizing antibodies, adoptive T-cell therapy or vaccines.