Background: BKV encodes two miRNAs from a single precursor: BKV-miR-B1-5p & BKV-JCV-miR-BJ1-3p. These viral miRNAs direct cleavage of large T antigen mRNAs, downregulate viral T antigen expression, target the stress induced ligand ULBP3, inhibit NKG-2D mediated killing of virus infected cells and help evade host immunity. The clinical utility of measuring these miRNAs has not been adequately explored. Potential applications include detection of very early latent infection and generating prognostic information.

Methods: A review of 836 samples sent out for BKV PCR over a course of 1 year, led to identification of (a) BKV positive urine samples with a concurrent plasma sample that was BKV negative (U+P-), and (b) urine samples with BK viruria and concurrent viremia (U+P+). RNA was extracted from plasma using the Qiagen miRNeasy Serum/Plasma Kit, and from urine using Trizol and SuperScript III Reverse Transcriptase. Amplification of BKV miRNAs was performed using RT stem-loop primers.

Results: The assays developed could detect 22 copies miR per ml. U+P- urine samples had a median viral load of 1.6E+09 BKV genomic equivalents/ml (range1.7E+08[mdash]2.8E+10). In the U+P+ group, the median urine BKV load was 4.7E+09 GE/ml (range 1.0E+09[mdash]8.8E+09) and the median plasma load was 1.3E+05 GE/ml (range 4.1E4-4.94E+05). BKV-miRNA was not detected in any plasma sample, even in those where viral DNA was demonstrable. In urine samples, BKV-miR-B1-5p was detected at a median concentration of 7.3E+09 cp/ml (range 1.29E+03[mdash]6.89E+04) in the U+P- group and 1.53E+04 cp/ml (range 1.36E+03-2.9E+04) in the U+P+ group. The concentrations of BKV-JCV-miR-BJ1-3p were always higher with a median

3p:5p ratio of 0.1 in the U+P- group and 0.03 in the U+P+ group. In scatter plots higher miR levels did not correlate with lower urinary or plasma viral load.

Conclusions: Viral miRNA amplification can be used to monitor BKV infection in assays that will not be affected by viral genotype, strain, or quasispecies, since the miRNA sequence is stable. Both miR-B1-5p and miR-BJ1-3p are transcribed in human infection, but their measurement in urine can not distinguish patients with BK viremia from those who only have BK viruria. However, failure to detect miRNA in the plasma suggests that advanced renal parenchymal injury is needed for release of viral miRNAs into the circulation. Thus, plasma miRNA assays could be a potential marker for BKV nephropathy.

CITATION INFORMATION: Randhawa P, Zeng G, Huang Y. Potential Applications of Viral miRNA Assays in the Management of Transplant Patients with Polyomavirus BK Infection. Am J Transplant. 2016;16 (suppl 3).

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