In vitro–expanded donor alloantigen–specific CD4+CD25+ regulatory T cells promote experimental transplantation tolerance

Abstract

IntroductionTransplantation of cells and organs is regarded as the only therapeutic choice for end-stage failure of several organs and has been made possible by the development of powerful immunosuppressive treatments that prevent transplant rejection. However, most of these drugs nonspecifically target the immune response, leading to unwanted side effects, and have limited ability to prevent chronic rejection. 1,2 The ultimate goal in transplantation is, therefore, the induction of a sustained state of specific tolerance to donor alloantigens with minimization or complete withdrawal of immunosuppression. Many studies in rodents have shown that it is possible to exploit the mechanisms that normally maintain immune homeostasis and tolerance to self-antigens to induce tolerance to alloantigens. 3 Immunologic tolerance involves central and peripheral mechanisms. Central tolerance results from intrathymic deletion of T cells with high avidity for thymically expressed antigens. Peripheral tolerance can be achieved by various mechanisms including deletion of activated/effector T cells, anergy induction, and active regulation of effector T cells. 4,5 CD4 ϩ T cells with regulatory function have been shown to play a critical role in the maintenance of transplantation tolerance. 6 The CD25 ϩ fraction of CD4 ϩ T cells mediates tolerance on adoptive transfer into a naive host. 7-9 CD4 ϩ CD25 ϩ regulatory T (Treg) cells are a naturally occurring population of CD4 ϩ T cells that constitutively express the IL-2 receptor ␣-chain (CD25). 10 These cells were shown to be potent suppressors of activated T cells in vitro 11,12 and to be crucial for the control of autoreactive T cells 13 and of the effector function of alloreactive CD4 ϩ and CD8 ϩ T cells in transplantation models in vivo. 8,14 The precise mechanisms by which these Treg cells exert their suppressive function remain to be defined. Surface molecules such as cytotoxic T lymphocyteassociated antigen 4 (CTLA-4), 15,16 the glucocorticoid-induced tumor necrosis factor receptor (GITR), 17 and cytokines such as TGF-␤ 18-20 and IL-10 8,21 are thought to play roles in different animal models.Several studies have implied that the regulation mediated by Treg cells is dependent on a continuous supply of alloantigens 8,[22][23][24] or tissue-specific target autoantigens, 25,26 suggesting that these cells have specificity for alloantigens or autoantigens. In transplantation, alloreactive CD4 ϩ T cells with indirect allospecificity are thought to play a key role in chronic rejection, and the control of these pathogenic effector cells by donor-specific Treg cells could, therefore, result in transplantation tolerance. [27][28][29][30][31] However, the possibility of using Treg cells as immunotherapy for the induction of antigen-specific tolerance is limited by cell number. Indeed, the entire pool of Treg cells accounts for only 5% to 10% of CD4 ϩ T cells in the peripheral blood of healthy persons. 10,32,33 In this study, we have explored whether in vivo alloresponses could be regulated...

Alloantigen‐specific de novo‐induced Foxp3+ Treg revert in vivo and do not protect from experimental GVHD

“…In vitro, these cells display suppressive activity similar to nTreg and when adoptively transferred to untreated syngeneic recipients, keep Foxp3 stably expressed. However, adoptive transfer of these cells has no beneficial effect in experimental GVHD, although it has been shown that allo-antigen-expanded Treg might be suitable to reduce allo-responses under noninflammatory conditions [21,22]. In experimental GVHD, iTreg are not stable and show only partial de-methylation of the Tregspecific demethylated region within the Foxp3 locus (data not shown), a phenomenon that seems to be common for in vitro generated iTreg [23].…”

“…Using GVHD, although it has been shown that allo-antigen-expanded Treg might be suitable to reduce allo-responses under noninflammatory conditions [21,22]. In experimental GVHD, iTreg are not stable and show only partial de-methylation of the Tregspecific demethylated region within the Foxp3 locus (data not shown), a phenomenon that seems to be common for in vitro www.eji-journal.eu generated iTreg [23].…”

Large-scale in vitro expansion of human regulatory T cells with potent xenoantigen-specific suppression

“…Selection and use of antigen-specific Treg has been proposed to improve Treg therapeutic efficiency and lower the risk for unwanted nonspecific immune suppression caused by transferring large numbers of polyclonal Treg (Koenecke et al 2009;Hall et al 2009;Peters et al 2008;Veerapathran et al 2011). Recent studies have shown that ex vivo expanded alloantigen specific Treg obtained enhanced suppressive capacity in allogeneic responses in vitro (Peters et al 2008;Golshayan et al 2007) and were more potent than polyclonal Treg in protecting against alloimmune-mediated injury of human skin grafts in a humanized mouse model (Yamano et al 2011;Sagoo et al 2011). However, strategies for large scale expansion of xenoantigen-specific human Treg remain to be developed.…”

“…Thus, clinically applicable strategies for immunomodulation need be developed to achieve tolerance to transplants by reducing or eliminating the requirement of immunosuppression. Regulatory T cells (Treg) have emerged as critically important for the control of autoimmunity and for the maintenance of allograft tolerance Brusko et al 2008;Wood and Sakaguchi 2003;Golshayan et al 2007). Recent studies have shown that human Treg are capable of suppressing CD4 ?…”

Allogeneic Mature Human Dendritic Cells Generate Superior Alloreactive Regulatory T Cells in the Presence of IL-15

“…Alloantigen-specific Tregs with a much greater specificity can be generated by expansion in the presence of allogeneic PBMCs (18,19) or B cells (10,20). The potential benefit of these alloantigen-specific Tregs is targeted suppression rather than general immunosuppression and increased suppressive potency (9,(21)(22)(23)(24)(25)(26). This may translate in fewer Tregs needed to have a therapeutic effect in the patient.…”