Post-transplant monitoring of cellular immunity might be useful in predicting long-term outcomes of kidney transplant recipients. We used an enzyme linked immunoabsorbent spot (ELISPOT) assay to serially measure the frequency of peripheral blood lymphocytes producing interferon-gamma in response to stimulator cells from donors or third parties in 55 primary kidney transplant recipients. Mean frequencies measured during the first 6 months after transplantation correlated significantly with the serum creatinine concentration at both 6 and 12 months following transplantation. The mean frequencies were higher in patients with acute rejection than in those without acute rejection. Multiple regression analyses indicated that the correlations between the early ELISPOT measurements of interferon-gamma and serum creatinine were independent of acute rejection, delayed graft function, or the presence of panel reactive antibodies before transplantation. Patients with low mean frequencies of interferon-producing cells in the early post-transplant period were generally free from acute rejection and exhibited excellent renal function at 6 and 12 months post-transplant. In conclusion, using the ELISPOT assay, we show an independent correlation between early cellular alloreactivity and long-term renal function. Increased levels of early alloreactivity measured with this assay may serve as a surrogate for chronic allograft dysfunction.

Post-transplant monitoring of cellular immunity has the potential to guide alterations in medical therapy. To this end, our laboratory has developed an enzymelinked immunosorbent spot (ELISPOT) assay for detection of peripheral blood alloimmunity. Peripheral blood lymphocytes (PBLs) from normal volunteers and from renal allograft recipients were tested against donor stimulator cells for their ability to respond in 'one-way' cytokine ELISPOT assays. T cell depletion of donor spleen or PBLs eliminated donor cell cytokine secretion while preserving the ability of these cells to present allo-antigen to responding T cells. Alloreactive IFNg-producing PBLs derive from the memory T cell pool and are readily detectable in recipients of renal allografts taking immunosuppressant medications. A significant expansion of IFN-g-producing donor-reactive memory PBLs was detectable at 4-6 months posttransplant in those who had experienced an acute rejection episode compared with those with a stable post-transplant course. The data demonstrate the feasibility of repeated post-transplant monitoring of allograft recipients, and provide the foundation for improving the care of human transplant recipients through rational clinical decision-making based on measures of immune function.

Abstract. The pathogenesis of chronic allograft nephropathy (CAN) involves both immunologic (antigen-dependent) and nonimmunologic (antigen-independent) mechanisms. In order to provide further insight into the immunologic basis of this disease, a cross-sectional analysis of cellular and humoral immunity in human renal allograft recipients with or without deteriorating renal function and biopsy proven CAN was performed. Interferon-␥ enzyme-linked immunosorbent spot assays were used to assess cellular immunity to donor, or fully mismatched third-party stimulator cells (direct pathway), and to synthetic peptides derived from donor HLA molecules (indirect pathway). Anti-HLA antibodies were evaluated by flow cytometry using HLA-coated beads. Both the mean frequencies of donor-reactive peripheral blood lymphocytes and the number of individuals who responded to donor antigens per group were statistically higher in CAN patients versus control subjects (P Ͻ 0.02). Calculated ratios of donor/third-party enzyme-linked immunosorbent spot responses showed mean values of 2.61 Ϯ 3.0 in the CAN group, with ratios of 0.50 to 0.72 Ϯ 0.42 in control subjects (P Ͻ 0.001), confirming that direct, donor-specific cellular immunity predominated in patients with CAN.

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