Intraperitoneal injection of IDO-expressing dermal fibroblasts improves the allograft survival

Genetically modified immunomodulatory cell-based biomaterials in tissue regeneration and engineering

To date, the wide application of cell-based biomaterials in tissue engineering and regeneration is remarkably hampered by immune rejection. Reducing the immunogenicity of cell-based biomaterials has become the latest direction in biomaterial research. Recently, genetically modified cell-based biomaterials with immunomodulatory genes have become a feasible solution to the immunogenicity problem. In this review, recent advances and future challenges of genetically modified immunomodulatory cell-based biomaterials are elaborated, including fabrication approaches, mechanisms of common immunomodulatory genes, application and, more importantly, current preclinical and clinical advances. The fabrication approaches can be categorized into commonly used (e.g., virus transfection) and newly developed approaches. The immunomodulatory mechanisms of representative genes involve complicated cell signaling pathways and metabolic activities. Wide application in curing multiple end-term diseases and replacing lifelong immunosuppressive therapy in multiple cell and organ transplantation models is demonstrated. Most significantly, practices of genetically modified organ transplantation have been conducted on brain-dead human decedent and even on living patients after a series of experiments on nonhuman primates. Nevertheless, uncertain biosecurity, nonspecific effects and overlooked personalization of current genetically modified immunomodulatory cell-based biomaterials are shortcomings that remain to be overcome.

Role of the thymus in spontaneous development of a multi-organ autoimmune disease in human immune system mice

We evaluated the role of the thymus in development of multi-organ autoimmunity in human immune system (HIS) mice. T cells were essential for disease development and the same T cell clones with varying phenotypes infiltrated multiple tissues. De novo-generated hematopoietic stem cell (HSC)-derived T cells were the major disease drivers, though thymocytes pre-existing in grafted human thymi contributed if not first depleted. HIS mice with a native mouse thymus developed disease earlier than thymectomized mice with a thymocyte-depleted human thymus graft. Defective structure in the native mouse thymus was associated with impaired negative selection of thymocytes expressing a transgenic TCR recognizing a self-antigen. Disease developed without direct recognition of antigens on recipient mouse MHC. While human thymus grafts had normal structure and negative selection, failure to tolerize human T cells recognizing mouse antigens presented on HLA molecules may explain eventual disease development. These new insights have implications for human autoimmunity and suggest methods of avoiding autoimmunity in next-generation HIS mice.

Tryptophan Metabolism via Kynurenine Pathway: Role in Solid Organ Transplantation

Solid organ transplantation is a gold standard treatment for patients suffering from an end-stage organ disease. Patient and graft survival have vastly improved during the last couple of decades; however, the field of transplantation still encounters several unique challenges, such as a shortage of transplantable organs and increasing pool of extended criteria donor (ECD) organs, which are extremely prone to ischemia-reperfusion injury (IRI), risk of graft rejection and challenges in immune regulation. Moreover, accurate and specific biomarkers, which can timely predict allograft dysfunction and/or rejection, are lacking. The essential amino acid tryptophan and, especially, its metabolites via the kynurenine pathway has been widely studied as a contributor and a therapeutic target in various diseases, such as neuropsychiatric, autoimmune disorders, allergies, infections and malignancies. The tryptophan-kynurenine pathway has also gained interest in solid organ transplantation and a variety of experimental studies investigating its role both in IRI and immune regulation after allograft implantation was first published. In this review, the current evidence regarding the role of tryptophan and its metabolites in solid organ transplantation is presented, giving insights into molecular mechanisms and into therapeutic and diagnostic/prognostic possibilities.

Indoleamine 2,3-dioxgenase-transfected mesenchymal stem cells suppress heart allograft rejection by increasing the production and activity of dendritic cells and regulatory T cells

Expression of indoleamine 2,3-dioxygenase (IDO) in mesenchymal stem cells (MSC) is thought to contribute to MSC-mediated immunosuppression. A lentiviral-based transgenic system was used to generate bone marrow stem cells (BMSC) which stably expressed IDO (IDO-BMSCs). Coculture of IDO-BMSCs with dendritic cells (DC) or T cells was used to evaluate the immunomodulatory effect of IDO-BMSCs. A heterotopic heart transplant model in rats was used to evaluate allograft rejection after IDO-BMSC treatment. Mechanisms of IDO-BMSC-mediated immunosuppression were investigated by evaluating levels of proinflammatory and anti-inflammatory cytokines, and production of Tregs. A significant decrease in DC marker-positive cells and a significant increase in Tregs were observed in IDO-BMSC cocultured. Treatment of transplanted rats with IDO-BMSCs was associated with significantly prolonged graft survival. Compared with the control groups, transplanted animals treated with IDO-BMSCs had a (1) significantly higher ejection fraction and fractional shortening, (2) significantly lower expression of CD86, CD80, and MHCII, and significantly higher expression in CD274, and Tregs, and (3) significantly higher levels of interleukin-10 (IL-10), transforming growth factor beta-1 (TGF-β1), TGF-β2, and TGF-β3, and significantly lower levels of IL-2 and interferon gamma. Our results expand our understanding of the molecular mechanisms underlying suppression of heart allograft rejection via IDO-expressing BMSCs.

Indoleamine 2,3-dioxygenase suppresses humoral alloimmunity via pathways that different to those associated with its effects on T cells

Chronic antibody-mediated rejection remains a major cause of late graft loss. Regarding cellular alloimmunity, the immunosuppressive properties of indoleamine 2,3-dioxygenase (IDO) have been well investigated; however, little is known of its effects on humoral alloimmunity. Therefore, the present study aimed to evaluate the effects of IDO on humoral alloimmunity. We developed a method for the induction of humoral alloimmunity in a one-way mixed lymphocyte reaction (MLR), which was measured with an antibody-mediated complement-dependent cytotoxicity assay using resting cells, which are similar to the stimulator cells of the aforementioned MLR. In parallel, cellular alloimmunity was assessed in two-way MLRs. The IDO inhibitor 1-methyl-DL-tryptophan was used for evaluating the role of IDO. In order to investigate whether the pathways known to serve a role in the effects of IDO on T cells are applied in humoral alloimmunity, the general control nonderepressible-2 (GCN-2) kinase activator tryptophanol and the aryl hydrocarbon receptor (AhR) inhibitor CH223191 were employed. The IDO inhibitor was revealed to increased cellular autoimmunity, but was decreased by the GCN-2 kinase activator. Unexpectedly, the AhR inhibitor decreased cellular alloimmunity. In addition, the IDO inhibitor was observed to suppress humoral alloimmunity, which may occur in manners independent of GCN-2 kinase AhR. The present study proposed that IDO may decrease humoral alloimmunity in primary human peripheral blood mononuclear cells via pathways that differ to those associated with its effect on T cells.