ASSAYS TO PREDICT ALLOGRAFT REJECTION

F.W.R. Vondran¹, K. Timrott¹, J. Tross¹, S. Kollrich¹, W. Gwinner², F. Lehner¹, J. Klempnauer¹, T. Becker¹, R. Schwinzer^1
1General, Visceral And Transplantation Surgery, Hannover Medical School, Hannover/GERMANY, ²Nephrology, Hannover Medical School, Hannover/GERMANY

Body: Introduction: Development of chronic allograft dysfunction (CAD) remains the most important limiting factor for long-term graft survival following kidney transplantation (Tx). The etiology of CAD is complex and still not fully understood but amongst others acute rejection (AR) has been identified as a major risk factor. Thus, identification of patients at risk for AR who would benefit from closer clinical surveillance to allow individual adaptation of the immunosuppressive protocol is highly desirable. Aim of the present study was to examine the association of pre-transplant T-cell alloreactivity and frequency of regulatory T-cells (T_regs) with acute rejection episodes in the first year after living kidney donor transplantation. Methods: Peripheral blood mononuclear cells (PBMC) were separated from heparinized blood samples obtained prior to Tx. All patients (n = 40) received triple immunosuppression consisting of a calcineurin-inhibitor, mycophenolate mofetil and prednisolone. Protocol biopsies as well as indicated biopsies were graded according to the updated BANFF classification. Proliferative responses in mixed lymphocyte cultures (MLC) were used to assess T-cell alloreactivity: 1x10⁵ PBMCs from kidney recipients were stimulated with the same number of gamma-irradiated (30 Gy) PBMCs from kidney donors and from HLA matched 3^rd party controls (same number of mismatches as for donor/recipient constellation), respectively. The pre-transplant frequency of CD4⁺CD25⁺CD127^lowFoxP3⁺ T_regs was determined by flow cytometry. Experimental data were correlated with the occurrence of acute rejection episodes. Results: MLC was performed in 36 patients (no adequate 3^rd party controls in 4 cases). Individuals with rejection-free Tx-courses (RF, n = 21) showed significantly lower pre-transplant T-cell alloreactivity to donor antigen compared to patients suffering from biopsy-proven borderline findings (BL, n = 9) or AR (n = 6) (8,594 ± 1,131, 16,216 ± 3,307 and 23,137 ± 2,958 counts per minute, respectively). Proliferative T-cell responses to 3^rd-party antigen were higher than for stimulation with donor cells in the RF-group whereas lymphocytes of individuals with AR showed the inverse pattern. Flow cytometry was performed in all patients and revealed comparable frequencies of CD4⁺CD25⁺FoxP3⁺ T_regs for RF (n = 23; 5.0 ± 0.4%), BL (n = 9; 4.7 ± 0.7%) and AR (n = 8; 4.1 ± 0.4% of CD4⁺ cells). However, the proportion of FoxP3⁺ cells within the CD4⁺CD25⁺CD127^low subset was significantly higher in the RF-group compared to patients with AR (52.3 ± 3.2% vs. 40.2 ± 3.3%, p = 0.038). Conclusions: Pre-transplant donor-specific T-cell alloreactivity and FoxP3 expression within the CD4⁺CD25⁺CD127^low subpopulation are different in patients with and without acute rejection episodes in the post-Tx course. These parameters might be useful to assess the individual risk for acute allograft rejection and to adjust the immunosuppressive regimen. Hence, further prospective studies with a larger number of patients are required to evaluate their reliability.

Disclosure: All authors have declared no conflicts of interest.