BK VIRUS INFECTION

H. Trydzenskaya¹, A. Sattler², K. Mueller², T. Schachtner³, A. Thiel², H. Volk², P. Reinke⁴, N. Babel^4
1Transplantation Research, Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Berlin/GERMANY, ², Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Berlin/GERMANY, ³, Charité-Universitätsmedizin Berlin, Berlin/GERMANY, ⁴Department Of Nephrology And Intensive Care Ccv, Charité-Universitätsmedizin Berlin, Berlin/GERMANY

Body: Introduction: BKV-associated nephropathy (BKVAN) represents a serious complication of the post-transplant period in kidney recipients leading to organ loss in 50 % of all cases. Being widely distributed in the normal population, BK virus (BKV) can reactivate in renal transplant patients leading to BKVAN. Monitoring of BKV-specific immunity is very important in management of patients with BKV infection and BKVAN. Our previous data demonstrated that all five BKV-specific antigens inducing CD4+ T-cell responses with BKV-antigenic immunodominance varying within affected patients. Therefore, BKV-specific T-cell response directed against all five BKV proteins should be analyzed in order to assess the entire BKV-specific immunity. The aim of the present study was to establish a fast/sensitive method for the analysis of BKV-specific CD4- and CD8- positive T cells and apply it for phenotypic and functional T cell analysis in renal transplant patients. Methods: Using mixture of overlapping peptide pools encompassing all 5 BKV antigens (VP1, VP2, VP3, LTAg and stAg) and multiparameter flow cytometry we evaluated BKV-specific CD4- and CD8- positive T cells in renal transplant patients with resolved BKV infection. Frequencies of BKV-specific CD4 and CD8-positive T cell responses were determined according to the expression of Interferon gamma (IFNg), Interleukin-2 (IL-2), Tumor Necrosis Factor alpha (TNFa) and Interleukin-17 (IL-17) alone and in combination to identify polyfunctional T cells. Results: Antigen-specific CD4- positive T cells were detectable in all transplant patients by single IFNg-producing T cells with frequencies ranging from 0.05-0.1% and single IL-2+ T cells ranging from 1.5-2.6%, respectively. Within the CD8-positive compartment IFNg+ cells clearly dominated the BKV-specific T cell response, being detectable in all patients at frequencies from 0.004-0.127% The frequencies of BKV-specific T cells demonstrated with the new protocol were significantly higher as compared to previously used methods. In addition, polyfunctional IFNg+IL-2+ and IFNg+IL-2+TNFa+ BKV-specific CD4+ T cells were found in all patients with resolved BKV infection and BKVAN. At the same time polyfunctional CD8+ T cells were rarely detected within studied patients. Interestingly, neither CD4- nor CD8-positive IL-17- producing cells were found. Conclusions: Here, we demonstrated, that, using mixture of overlapping peptides pools spanning all five BKV proteins enabled us to identify CD4- and CD8- positive T cell responses and their phenotypic/functional characteristics that were not consistently detectable with the previously applied protocol with a single protein stimulation. Thus, our results have significant clinical implication for monitoring of the complete BKV-specific cellular immunity as a predictive risk factor for the progression of BKV infection and BKVAN.

Disclosure: All authors have declared no conflicts of interest.