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Novel Approach for Improved Assessment of Phenotypic and Functional Characteristics of BKV-Specific T-Cell Immunity

Background. BKV-associated nephropathy represents a serious complication of the posttransplant period in kidney transplant recipients. Monitoring BKV-specific immunity is of a special importance for estimation of clinical course in patients with BKV reactivation. Our recent data demonstrated that all five BKV antigens are immunogenic and elicit T-cell responses varying within patients. Therefore, all five BKV proteins should be evaluated for the assessment of BKV-specific immunity. However, analysis of five proteins performed separately is time- and cost-intensive and requires large amount of blood. Methods. Using novel approach of a mixture of overlapping peptide pools encompassing all five BKV antigens (viral protein [VP] 1, VP2, VP3, large tumor antigen, and small tumor antigen) and multiparameter flow cytometry, we evaluate BKV-specific T cells in patients with a previous/present severe long-lasting or transient BKV reactivation. Patients without BKV reactivation were used as control. Results. In this study, we show that using mixture of overlapping peptide pool results in the magnitude of CD4- and CD8-positive BKV-specific T-cell response, which is significantly higher compared with any frequencies detected by previously used single BKV antigen stimulation. Of interest, patients with a history of rapid BKV clearance had significantly higher frequency of multifunctional interferon gamma-&ggr;/interleukin (IL)-2/tumor necrosis factor-&agr; and IL-2/tumor necrosis factor-&agr; CD4-positive T cells, suggesting protective potential of polyfunctional T cells. Furthermore, we did not find IL-17-producing BKV-specific memory T cells in patients recovered from BKV reactivation. Conclusions. Here, we established a fast and sensitive approach allowing the most comprehensive assessment of the total BKV immunity performed to date and offer a new platform for further prospective studies.