#3944 Natural killer subpopulations in kidney transplant patients with BK viruria

Abstract Background and Aims Infection in kidney transplant recipients (KTR) is, with cardiovascular disease, an important cause of morbidity and mortality. During last two decades, polyomavirus BK incidence has increased notably, being nowadays the most important virus targeting kidney tissue. As there is no directed treatment proved efficient, reduction in immunosuppression is the standard of care to control BK replication. Owing that this measure suppose a rise in rejection risk, identify patients at risk of BK nephropathy is crucial. Immune response study has raised interest during last years. Although virus-specific T cells plays a main role in elimination of reactivated BK, natural killer (NK) cells also are a central component of innate immune system against virus, so that their response in KTR has been studied in other viral infection as cytomegalovirus and herpesvirus. Method In our centre we perform screening for BK viruria by urine PCR in KTR monthly after transplantation until month 6, and afterwards at month 9 and 12 post-transplantation. We conduct a descriptive, observational and transversal study, to assess lymphocyte subpopulations in KTR who present viruria (defined by urine BK PCR >10x106 copies/ml) compared to KTR without viruria. Using flow cytometry we assessed lymphocyte subpopulations in blood at diagnosis of viruria in cases and at reclutation time in controls. In cases, we determined subpopulations for a follow up period of 2 months. Data were analyzed with SPPS 20.0; Chi square, Student-t and Wilcoxon tests are applied. Results 24 patients were studied, 14 cases and 10 controls. Clinical characteristics are presented in Table 1, with no statistical difference between groups. Number of NK cells in blood is higher in patients with BK viruria at the moment of diagnosis (110 [SD 95.2] vs 66.2 [SD 36.4], p=0.18). Assessing NK subpopulations, number of CD56+ and CD56+CD27- cells are higher in KTR with viruria (99.76 [89.41] vs 59.85 [34.62], p=0.19; 93.68 [85.27] vs. 55.74 [33.8], p=0.19) (Fig. 1). In the follow-up period for BK viruria KTR, we observed decreased number of CD56++ cells (p=0.22), a rise in CD56+ CD27+ cells (p=0.15), and steady number of CD56+ cells and CD56+ CD27- cells (p=0.51, and p=0.47; respectively). The same trend is observed at month 2 (no statistical significance). Conclusion NK cells respond early during viral infection, a rapid activation could explain a rised number in patients with viral BK replication detected in urine. The majority of NK cells in circulating blood are CD56+, and most do not express CD27. NK CD27- contains higher levels of perforin and granzyme, meaning a cytotoxic activity, as expected in patients at earlier stages of viral replication. Although the results did not reach statistical significance, due in part to small sample, we can elucidate how the assessment of innate immunity can play a role in the evaluation of KTR with BK virus reactivation, and settled basis for further research.