Role Of Regulatory T Cells In Transplant Tolerance And Alloreactive T Cell In Clonal Deletion

Background and objectiveImmunosuppressive regimens capable of inducing and maintaining tissue-specific tolerance will eventually replace life-long immunosuppressive treatment in organ transplantation. Short-term treatment with costimulation and coreceptor blockade induces robust and lasting tolerance, and exposes mechanisms that can be exploited to reprogram the peripheral immune system.Committed Foxp3+ Tregs derived from the thymus or peripheral immune system form a largely stable T-cell lineage, can be identified by demethylation of the Treg-specific demethylated region and have therapeutic potential.Regulation of Foxp3 expression and Foxp3+ Treg lineage commitment is under epigenetic control and can be targeted therapeutically.In the peripheral immune system, Foxp3 expression induced in naive CD4+ T cells in the presence of antigen can, in principle, generate stable and committed Foxp3+Treg generation in vivo.Transplantation tolerance via coreceptor and costimulation blockade depends on the in vivo induction of Foxp3+ Tregs and their continuous presence. However, these antibodies are not currently available for routine clinical use.Transplantation tolerance can now be achieved in several animal models following different approaches, with the common theme being induction of Foxp3+ Tregs in vivo. Clinical translation of these animal studies may be facilitated by the emergence of pharmacological compounds potentiating regulation. Establishing the rules for enhancing Foxp3+ Tregs from within the patient is therefore likely to yield attractive and novel approaches to minimize immunosuppression in graft recipients.MethodsF1 mice were bred by crossing female BALB/c mice and male C57BL/6 mice. Within 24 h, newborn C57BL/6 mice were inoculated with F1 spleen cells via the orbital branch of the anterior facial vein. Six weeks later, the mice were subjected to F1 skin grafting to evaluate their tolerance. Proliferation, flow cytometry and adoptive transfer assay were used to analyze clonal deletion of alloreactive T cells and the expression of CD4+Foxp3+ T cells in neonatal treated mice.ResultsNewborn C57BL/6 mice injected with F1 splenic cells could induce transplantation tolerance, the level of tolerance was associated with the dose of splenic cells.3×107 splenic cells from F1 mice could induce long-term skin graft acceptance in C57BL/6 mice, 1×107splenic cells significantly prolonged the survival of F1 skin grafts, but the grafts completely rejected within 50 days. The mixed lymphocyte reaction (MLR) experiment in vivo showed that alloreactive T cell in long-term tolerant mice was deleted completely, but a certain amount of reactive T cells existed in the low-dose group mice. Flow cytometry (FCM) analysis showed that the expression of CD4+Foxp3+ T cell in the high-dose group and low-dose group mice had no obvious difference compared with the naive mice. When alloreactive T-cells were injected into tolerant mice, the skin graft rejection was observed, and Treg cells upregulated in graft-rejected mice.ConclusionsThe degree of transplantation tolerance depended on the clonal deletion of alloreactive T cells, instead of on the expression of CD4+Foxp3+ Treg cells. CD4+Foxp3+ regulatory T cells upregulated in graft rejected mice, which may be served as a negative feedback mechanism to control the intensity of rejection.