Quantitation of DNA of polyomaviruses BK and JC in human kidneys

Background. Renal allograft recipients can be monitored for polyomavirus-associated nephropathy ( PVAN) using urine samples. Because virus in urine can be derived from the kidneys, ureter, or urinary bladder, we evaluated whether measurement of intrarenal concentrations of viral DNA might serve as a more reliable monitoring tool. Methods. Real-time quantitative polymerase chain reaction was used to quantitate DNA of polyomaviruses BK (BKV) and JC (JCV) in renal tissue obtained from various clinical settings. Results. Renal biopsy samples from 28 nonimmunosuppressed patients contained very low viral copy numbers. Minimally higher BKV loads (mean +/- SE, 3.4 +/- 1.7 copies/ cell) were observed in 74 renal biopsy samples from renal allograft recipients with BKV viruria. The BKV DNA concentration was similar to 10-fold higher in renal allograft recipients with BKV viruria, but 58 (50.4%) of 115 renal biopsy samples tested negative for BKV DNA, reflecting the focal nature of infection. JCV DNA was found in only 2 renal biopsy samples. Conclusions. The BKV load is better measured in urine than in tissue, because a urine sample represents material from the entire kidney. An increase in the BKV load is usually not accompanied by a proportional increase in the JCV load, which indicates that these 2 related polyomaviruses are subject to different mechanisms regulating viral replication.