T-cell tolerance through dendritic cells expressing IDO

This present proposal applies for continuation of our previous project "Exploration of the tolerance inducing capacity of indoleamine 2,3 dioxygenase (IDO) in antigen presenting cells" (FWF grant # P16746-B13). It represents a further step of our continuing scientific effort to ex vivo generate T cells, which are specifically tolerized against allo-antigens. Such T cells are potentially suitable for adoptive transfer strategies to recipients of hematopoietic stem cell transplantation (HSCT) as they, according to our hypothesis, may transfer competent T cell immunity against pathogens but without aggravating the risk of graft-versus-host disease (GvHD). These adoptively transferred T cells may be particularly helpful during the phase of post-HSCT immunocompromise, in which HSCT recipients are highly susceptible to pathological immune reactions (including GvHD) and opportunistic life-threatening infections. In the preceding project we have achieved some major milestones towards the generation of immunological tolerance employing the tryptophan catabolizing activity of indoleamine-2,3 dioxygenase (IDO) in human dendritic cells (DCs): (1) Human monocyte-derived DCs can reliably be induced to display high IDO activity by defined maturation stimulation strategies. (2) IDO competent DCs down-regulate allo-antigen induced T cell responses as they (i) favor the differentiation of allo-antigen activated T cells into a population with a regulatory phenotype and function, and (ii) appear to be involved in apoptosis induction in allo-antigen activated T cells. (3) Non-allo- specific T cells retain their capacity to be stimulated by nominal antigens even after co-culture with IDO competent DCs. All together these findings strongly supports our hypothesis, which is that allo-antigen-specific tolerance in T cells can be achieved through an ex vivo co-culture with IDO competent DCs. The goal of this continuing proposal now is to further test the above hypothesis with a specific focus on the antigen-specificity of the induced T cell tolerance. We therefore will investigate in particular (i) the mechanisms of apoptosis induction (i.e. mechanism and effectiveness of elimination of allo-reactive, but not of non-allo-reactive, T cells by IDO competent allogeneic DCs), and (ii) the effects of IDO competence on the phenotype and cytokine profile in DCs and the responding T cells, intending to possibly optimize and fine-tune tolerance induction. In addition we will study the role of exogenous interleukin-2 for its reported ability to promote the expansion of regulatory T cells and concomitantly increase the antigen-specificity of their suppressor activity. The successful completion of the study will set a further indispensable pre-clinical step on our way of developing strategies to ameliorate the risks currently being associated with human HSCT. By such an approach HSCT can be potentially offered as a safe mode of treatment to a wider spectrum of patients, for whom it may be a curative option.

This present proposal applies for continuation of our previous project "Exploration of the tolerance inducing capacity of indoleamine 2,3 dioxygenase (IDO) in antigen presenting cells" (FWF grant # P16746-B13). It represents a further step of our continuing scientific effort to ex vivo generate T cells, which are specifically tolerized against allo-antigens. Such T cells are potentially suitable for adoptive transfer strategies to recipients of hematopoietic stem cell transplantation (HSCT) as they, according to our hypothesis, may transfer competent T cell immunity against pathogens but without aggravating the risk of graft-versus-host disease (GvHD). These adoptively transferred T cells may be particularly helpful during the phase of post-HSCT immunocompromise, in which HSCT recipients are highly susceptible to pathological immune reactions (including GvHD) and opportunistic life-threatening infections. In the preceding project we have achieved some major milestones towards the generation of immunological tolerance employing the tryptophan catabolizing activity of indoleamine-2,3 dioxygenase (IDO) in human dendritic cells (DCs): (1) Human monocyte-derived DCs can reliably be induced to display high IDO activity by defined maturation stimulation strategies. (2) IDO competent DCs down-regulate allo-antigen induced T cell responses as they (i) favor the differentiation of allo-antigen activated T cells into a population with a regulatory phenotype and function, and (ii) appear to be involved in apoptosis induction in allo-antigen activated T cells. (3) Non-allo- specific T cells retain their capacity to be stimulated by nominal antigens even after co-culture with IDO competent DCs. All together these findings strongly supports our hypothesis, which is that allo-antigen-specific tolerance in T cells can be achieved through an ex vivo co-culture with IDO competent DCs. The goal of this continuing proposal now is to further test the above hypothesis with a specific focus on the antigen-specificity of the induced T cell tolerance. We therefore will investigate in particular (i) the mechanisms of apoptosis induction (i.e. mechanism and effectiveness of elimination of allo-reactive, but not of non-allo-reactive, T cells by IDO competent allogeneic DCs), and (ii) the effects of IDO competence on the phenotype and cytokine profile in DCs and the responding T cells, intending to possibly optimize and fine-tune tolerance induction. In addition we will study the role of exogenous interleukin-2 for its reported ability to promote the expansion of regulatory T cells and concomitantly increase the antigen-specificity of their suppressor activity. The successful completion of the study will set a further indispensable pre-clinical step on our way of developing strategies to ameliorate the risks currently being associated with human HSCT. By such an approach HSCT can be potentially offered as a safe mode of treatment to a wider spectrum of patients, for whom it may be a curative option.