The genetic predisposition of natural killer cell to BK virus-associated nephropathy in renal transplant patients.

BK virus (BKV) infection represents a serious complication in renal transplant patients resulting in BKV-associated nephropathy and subsequent allograft loss. Natural killer cells are crucial in the antiviral immune response; however, an understanding of the role of natural killer cells in protection against BKV is limited. To elucidate whether killer-cell immunoglobulin-like receptors and their interaction between donor-/recipient-related ligands have a role in BKV infection, we performed genotyping analysis in 48 kidney transplant recipients with a history of severe BKV infection/BKV-associated nephropathy and 110 recipients with stable renal function and no BKV reactivation. Of interest, we found that telomeric gene content motif was significantly associated with severe course of BKV infection/BKV-associated nephropathy and detected significantly higher percentage of patients with BKV-associated nephropathy carrying low numbers of activating receptors compared with the control group. Detailed analysis of each single receptor revealed significantly lower frequencies of the activating receptor KIR3DS1 in patients with BKV infection/nephropathy as compared with the controls. Thus, our study supports protective effects of activating receptors in BKV infection and suggest natural killer-cell-related genetic predisposition to the development of BKV-associated nephropathy.

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-γ/interleukin (IL)-2/tumor necrosis factor-α and IL-2/tumor necrosis factor-α 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.

BK-VP3 as a new target of cellular immunity in BK virus infection.

BACKGROUND: Polyomavirus BK virus (BKV) infection represents a serious complication leading to BKV-associated nephropathy (BKVAN) and subsequent kidney graft loss in up to 10% of transplant patients. Cellular immunity is known to play a crucial role in the control of BKV replication. However, the knowledge on the BKV-T-cell response is limited: only two (VP1 and large T antigen) of six known BKV proteins were evaluated for their antigenicity so far. METHODS: By using 10-color flow cytometry and newly created overlapping peptide pools of five BKV antigens (VP1, VP2, VP3, large T antigen, and small t antigen), we performed cross-sectional phenotypic and functional analysis of BKV-specific T cells in kidney transplant patients with a history of BKVAN. Patients with clinically unapparent BKV infection (history of transient/no BKV reactivation) were used as control group. RESULTS: Our data demonstrate for the first time the antigenic properties of all five evaluated proteins with VP3 as a new important target of cellular immunity. Further, we found a correlation between the severity of the previous BKV infection and the magnitude of memory CD4+ T-cell response. Thus, compared with the control group, patients with a history of BKVAN demonstrated significantly higher frequencies of interferon-γ- and interleukin-2-producing effector memory CD4+ T cells. In the control group, more patients with detectable interferon-γ+/interleukin-2+/tumor necrosis factor+ triple producers were found, suggesting possibly a protective function of these multifunctional T cells. CONCLUSIONS: In conclusion, our study results suggest an implementation of new targets for monitoring of BKV immunity. Further studies are required to evaluate the protective function of the found BKV-specific T-cell subsets.