Human Regulatory T Cells with Alloantigen Specificity Are More Potent Inhibitors of Alloimmune Skin Graft Damage than Polyclonal Regulatory T Cells

Abstract

Graft rejection by the immune system is a major cause of transplant failure. Lifelong immunosuppression decreases the incidence of graft rejection; however, nonspecific immunosuppression results in increased susceptibly to infection and cancer. Regulatory T cells (Tregs), which suppress the activation of the immune system and induce tolerance, are currently under evaluation for use in clinical transplantation. Ex vivo expanded polyclonal Tregs that are introduced into transplant recipients alter the balance of T effector cells to Tregs; however, experimental data suggest that alloantigen-specific Tregs would be more effective at preventing graft rejection. We have developed a method to enrich alloantigen-specific human Tregs based on the coexpression of activation markers, CD69 and CD71. These Tregs could be readily expanded in vitro and demonstrated potent antigen-specific suppression. In a humanized mouse model of alloimmune-mediated injury of human skin grafts, alloantigen-specific Tregs resulted in a significant reduction in clinically relevant indicators of dermal tissue injury when compared with polyclonal Tregs, restoring a histology comparable to healthy skin. This method of human allospecific Treg selection should be scalable to the clinic. The improved in vivo efficacy of alloantigen-specific Tregs over polyclonal Tregs shown here suggests that generating “customized” Tregs with defined anti-donor allospecificities may improve current practice in clinical immunotherapy.

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

“…This is most likely the result of a skewing in the TCR repertoire imposed by application of an Ag-specific expansion protocol (10,20). This superior alloantigenspecific suppressive capacity, induced by applying an allogeneic stimulus during Treg expansion, was confirmed by several in vitro (18) and in vivo (9,26,66) studies. In addition, allogeneic mature moDC-expanded nTregs had a differential expression profile of homing receptors compared with not-expanded or polyclonalexpanded nTregs, enabling a more efficient migration to peripheral tissues to exert suppressive function "onsite."…”

“…Data from transplantation models using animals have also shown the efficacy of Tregs in controlling the alloreactive immune response, thereby preventing or delaying allograft rejection. Moreover, in a humanized mouse skin transplant model, alloantigen-specific Tregs were superior in controlling skin rejection compared with polyclonal-expanded Tregs (9,10).…”

“…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.…”

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.…”

“…However, the infused polyclonal Treg may also deliver panimmunosuppressive effects, such as opportunistic infections and tumor-growth. Studies with transplantation animal models and immune monitoring of transplant patients indicate that these side effects could be avoided by specific suppression of the expansion of donor-alloreactive effector T cells after transplantation, which can be achieved by using donor allospecific Treg that are more effective at preventing allograft and improving clinical outcome than polyclonal Treg (Masteller et al 2006;Peters et al 2008;Sagoo et al 2011).…”