Switching from tacrolimus(Tac) to low-dose cyclosporine A(CsA) is recommended for preventing BK virus-associated nephropathy(BKVAN) and preserving allograft function in BKVAN patients, but systematic evaluations were not performed in previous studies.

Between 2006 and 2014, we routinely screen for decoy cells by quantitative assay, BKV DNA load in urine and plasma, and transplant biopsies by simian virus 40 staining in renal transplant patients received graft biopsy. Based on allograft biopsy results and BKV-viremia or viuria, patients(n=84)who were received switching from Tac to CsA, were assigned to three groups: (i) definitive BKVAN(n=19), (ii) presumptive BKVAN defined by plasma BKV-loads of ≥1×10⁴copy/ml(n=17) and (iii) high viruria(urine BKV-loads of ≥1×10⁷copy/ml (n=48). These patients were monitored for BKV every 1-4 weeks during the follow-up.

At diagnosis, the median level of decoy cells, viruria, viremia were 10/10HPF, 2.7 ×10⁸copy/ml, and 1.2×10⁴copy/ml, respectively. Patients with definitive BKVAN had higher plasma BKV-loads(median: 1.5×10⁵copy/ml vs. 2.5×10⁴copy/ml vs. 3.2×10³copy/ml), larger number of decoy cells(20/10HPF vs. 9/10HPF vs. 5/10HPF), and higher serum creatinine level (188.9±39.5 vs. 139.6±23.3 vs.130.6±16.7¯o;mol/L) than patients with presumptive BKVAN and high viruria( All P <0.05). After switching from Tac to low-dose CsA (mean time of follow-up: 30.5±15.2 months), clearance of decoy cells, viruria, and viremia were achieved in 67/74(90%), 67/84(80%), and 39/41(95%) patients. No subsequent clinical rejection occurred. Patients with definitive BKVAN required longer time for viremia clearance (6.1 vs. 4.6 vs. 1.9 months; all p <0.05) and decoy cells clearance (9.8 vs. 4.9 vs. 3.3 months; all p <0.05). However, allograft function remained stable from baseline to last follow-up in group ii and iii with mean serum creatinine of 127.6±13.7 and 115.6± 12.8¯o;mol/L, respectively. In group i, except 4 graft were lost, allograft function was 203.9± 86.5¯o;mol/L. The mean CsA trough level at last follow-up in the three groups were 85.3±36.6, 92.6±38.6, and 100.2±35.7 ng/ml, respectively.

It is concluded that screening for BKVand switching from Tac to low-dose CsA is an effective and safe strategy to preserve allograft function in presumptive BKVAN patients even in definitive BKVAN.

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