Reversibility with Interleukin-2 Suggests that T Cell Anergy Contributes to Donor-Specific Hyporesponsiveness in Renal Transplant Patients

Abstract

Abstract. Data from various rodent models have implicated a role for anergic T cells in the maintenance of self and transplantation tolerance. The relevance of donor-specific T cell anergy to clinical transplantation, however, has not been demonstrated. Previous studies have reported that recipients of solid organ transplant often have reduced frequencies of CD4 ϩ T cells with anti-donor direct pathway allospecificity after transplantation. The underlying mechanism(s) of this donorspecific hyporesponsiveness is unclear but likely to contribute to the diminished immunosuppressive requirement of transplant patients with time after transplantation. This study shows that ex vivo treatment of CD4 ϩ T cells from renal transplant recipients with IL-2 could specifically increase the anti-donor frequency in all the patients with evidence of donor-specific hyporesponsiveness. It also shows that the IL-2-induced recovery of anti-donor frequency is unlikely to result from nonspecific stimulation or selective clonal expansion of activated, allospecific CD4 ϩ T cells. Taken together, the data suggest that T cell anergy plays an important role in the direct pathway hyporesponsiveness that evolves in many human renal transplant recipients.Heightened interest in clinical transplant tolerance stems from the acquisition of insights into the mechanisms and the advent of novel biologic reagents that may promote such a tolerant state. For these reasons, it is necessary to understand the evolution of anti-donor responses using current approaches to immunosuppression. We and others (1-3) have previously described that a substantial proportion of patients with kidney or other solid organ transplants have markedly reduced numbers of T cells with direct allospecificity, particularly in longterm live-related transplant recipients. Although markedly decreased frequencies of direct pathway T cells does not equate to tolerance, it is tempting to speculate that mechanisms that contribute to peripheral T cell tolerance may be operative in diminishing the anti-donor T cell repertoire. It is also important to note that direct pathway hyporesponsiveness can often be observed in patients with chronic transplant rejection. In these patients, it appears that the indirect pathway of anti-donor alloimmunity provides an immunologic drive to this indolent process.Two attractive, yet not mutually exclusive, candidate mechanisms of direct pathway hyporesponsiveness are deletion and anergy. In vitro studies using renal epithelial cells as antigenpresenting cells can result in T cell anergy (4), and peripheral deletion has been shown to be an important mechanism in maintaining tolerance to foreign antigens (5,6). In this study, we investigated whether these mechanisms are operative in the maintenance of donor-specific hyporesponsiveness. Because of the lack of known specific marker of anergic cells, we have relied on the functional properties of anergic T cells to distinguish these possibilities. One of the characteristics of anergic T cells is that their re...

Regulatory T Cells in Kidney Transplant Recipients

“…Thus, they concluded that CD4 ϩ CD25 ϩ T cells are not the major regulators responsible for donor-specific direct T cell hyporesponsiveness. This conclusion is supportive of their previous experimental results showing anergy as one of the mechanisms of hyporesponsiveness of anti-donor T cells in the direct pathway (12).…”

Regulation of myeloperoxidase‐specific T cell responses during disease remission in antineutrophil cytoplasmic antibody–associated vasculitis: The role of Treg cells and tryptophan degradation

“…Depletion was confirmed by flow cytometry using directly conjugated anti-CD4 and anti-CD25 monoclonal antibodies (both from PharMingen) using a FACSCalibur (Becton Dickinson) and analyzed with CellQuest software (Becton Dickinson). In further experiments, one fraction of cells was treated with exogenous IL-2 (30 units/ml; Roche Diagnostics) for the duration of the assay, as previously described (16). Finally, Treg cells were isolated with CD4CD25 beads (Miltenyi), and purified CD4CD25ϩ cells were used to suppress the response of CD4CD25Ϫ cells stimulated (in a ratio of 1 Treg cell to 10 effector cells) with CD3CD28 expansion beads (Dynal).…”

“…To investigate the factors regulating low T cell frequencies in patients with disease in remission, we repeated T cell assays with depletion of potential Treg cells or with the addition of exogenous IL-2 to reverse T cell anergy, as previously described (15,16). Responses to tetanus or mumps antigen were used as controls.…”

“…The notion that tryptophan degradation was due to monocyte/macrophage up-regulation of IDO through the action of proinflammatory cytokines was supported by the presence of elevated levels of serum neopterin in patients with acute disease and patients with disease in remission. Neopterin is a low molecular mass product of monocyte/macrophages, the up-regulation of which is similarly influenced by proinflammatory cytokines such as IFN␥ (13 [8][9][10][11][12][13][14][15][16][17][18][19][20] in healthy controls; P Ͻ 0.001 for patients with acute disease versus controls and P Ͻ 0.05 for patients with disease in remission versus controls, by one-way ANOVA) ( Figure 4C). Serum neopterin levels remained elevated in patients compared with controls when corrected for renal function.…”

How Can We Measure Immunologic Tolerance in Humans?

“…Anergy is a second mechanism that may contribute to transplantation tolerance (13). Anergy refers to a long-lasting state of partial or total unresponsiveness that develops after suboptimal or incomplete T cell activation (reviewed in reference [14]).…”