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In previous work, the authors demonstrated that kidney transplant recipients developed donor-specific unresponsiveness when they were given a pretransplant infusion of modified donor-derived PBMCs. In this study, they provide evidence that the immunosuppressive properties of these cells persist and the donor-specific unresponsiveness is long-lasting. In the four patients who received the highest dose of the modified immune cells, administration of these cells was associated with a striking increase in IL-10–producing regulatory B lymphocytes and evidence of the consensus gene expression signature of operational tolerance. In vitro, donor-specific unresponsiveness was abolished after B lymphocyte depletion, suggesting a direct pathophysiologic role for regulatory B lymphocytes. These findings support the notion that modified donor-derived PBMCs may be useful in kidney transplantation, but this approach requires further validation and rigorous controlled randomized studies.

Naturally occurring regulatory T cells have been associated with long-term allograft survival. We investigated whether gene transcripts of Treg-related molecules are upregulated or downregulated in kidney transplant recipients with different clinical outcomes and may serve as markers of operative tolerance.

The mechanisms underlying long-term acceptance of kidney allografts in humans under minimal or no maintenance immunosuppression are poorly understood. We analyzed the T-cell receptor (TCR) repertoires in circulating T cells of patients with long-term (≥9 years) renal allograft survival with (LTS-IS) and without immunosuppression (LTS-NoIS). T cells of LTS patients exhibited strongly altered TCR Vß usage, including an increased frequency of oligoclonality and a decreased frequency of polyclonality. All 3 LTS-NoIS and 12 of 16 LTS-IS patients demonstrated oligoclonality in at least three or more TCR Vß families, and the frequency of oligoclonality in these patients was significantly higher as compared to patients with well-functioning grafts at 3 years (p < 0.005 both), an uncomplicated course during the first year (p < 0.0001, both), acute rejection (p < 0.0001, both), chronic allograft nephropathy at 7 (p < 0.0001, both) or 13 years (p < 0.0001, both), dialysis patients (p < 0.0001, both) or healthy controls (p < 0.0001, both). In contrast to LTS patients, all other studied patient groups exhibited a polyclonal TCR repertoire. Our data indicate that TCR alteration is a common feature of long-term allograft outcome, which might be explained by clonal deletion, exhaustion of alloreactive T cells or predominant expression of particular T-cell subpopulations, such as regulatory T cells.

The mechanisms underlying long-term acceptance of kidney allografts in humans under minimal or no maintenance immunosuppression are poorly understood. We analyzed the T-cell receptor (TCR) repertoires in circulating T cells of patients with long-term (≥9 years) renal allograft survival with (LTS-IS) and without immunosuppression (LTS-NoIS). T cells of LTS patients exhibited strongly altered TCR Vß usage, including an increased frequency of oligoclonality and a decreased frequency of polyclonality. All 3 LTS-NoIS and 12 of 16 LTS-IS patients demonstrated oligoclonality in at least three or more TCR Vß families, and the frequency of oligoclonality in these patients was significantly higher as compared to patients with well-functioning grafts at 3 years (p < 0.005 both), an uncomplicated course during the first year (p < 0.0001, both), acute rejection (p < 0.0001, both), chronic allograft nephropathy at 7 (p < 0.0001, both) or 13 years (p < 0.0001, both), dialysis patients (p < 0.0001, both) or healthy controls (p < 0.0001, both). In contrast to LTS patients, all other studied patient groups exhibited a polyclonal TCR repertoire. Our data indicate that TCR alteration is a common feature of long-term allograft outcome, which might be explained by clonal deletion, exhaustion of alloreactive T cells or predominant expression of particular T-cell subpopulations, such as regulatory T cells.

Patients with long-term functioning organ allografts may have developed different mechanisms that explain the lack of graft rejection. However, it is not known how these mechanisms interplay or whether one of them predominates in such situations.