BKV-associated nephropathy (BKVAN) causing kidney graft impairment is often difficult to distinguish from acute rejection (AR). A misdiagnosis may be detrimental to the patient, because the treatment strategies are diametrically opposed. Diagnostic markers especially of non-invasive nature allowing differentiation between BKVAN and AR will be important.

In the present study 38 renal transplant patients including BKVAN (n=13), AR (n=13) and transplant patients with stable graft function (n=12) were analysed. Expression of urinary mRNA for cytotoxic T cell markers like granzyme B (GB), programmed cell death-1 (PD1), and regulatory T cell-related markers like FOXP3, GATA3 and GAL1 and also mRNA for CD3 and HPRT were measured by quantitative PCR. Additionally protein expression of PD1, CD3 and GB were analysed by immunohistochemical staining in renal allograft tissue biopsies.

The expression of urinary GB, FOXP3, GATA3 and GAL1 mRNA in urinary cells were significantly higher in AR patients compared to patients with BKVAN (p=0.015, p=0.026, p=0.01, p=0.038, respectively) or stable graft function (p=0.001, p=0.026, p=0.004, p=0.001, respectively). Protein expression of PD1 and GB in biopsies was higher in AR and BKVAN compared to the patients with stable graft function.

In this study we identified non-invasive diagnostic markers including FOXP3, GB, GATA3 and GAL-1 in urine facilitating a distinct delimitation of BKVAN and AR.

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