Dominic Boardman

CD73 expression on extracellular vesicles derived from CD4(+) CD25(+) Foxp3(+) T cells contributes to their regulatory function

CD4+CD25+Foxp3+ Treg cells maintain immunological tolerance. In this study, the possibility that Treg cells control immune responses via the production of secreted membrane vesicles, such as exosomes, was investigated. Exosomes are released by many cell types, including T cells, and have regulatory functions. Indeed, TCR activation of both freshly isolated Treg cells and an antigen‐specific Treg‐cell line resulted in the production of exosomes as defined morphologically by EM and by the presence of tetraspanin molecules LAMP‐1/CD63 and CD81. Expression of the ecto‐5‐nucleotide enzyme CD73 by Treg cells has been shown to contribute to their suppressive function by converting extracellular adenosine‐5‐monophosphate to adenosine, which, following interaction with adenosine receptors expressed on target cells, leads to immune modulation. CD73 was evident on Treg cell derived exosomes, accordingly when these exosomes were incubated in the presence of adenosine‐5‐monophosphate production of adenosine was observed. Most importantly, CD73 present on Treg cell derived exosomes was essential for their suppressive function hitherto exosomes derived from a CD73‐negative CD4+ T‐cell line did not have such capabilities. Overall our findings demonstrate that CD73‐expressing exosomes produced by Treg cells following activation contribute to their suppressive activity through the production of adenosine.

MicroRNAs affect dendritic cell function and phenotype

MicroRNA (miRNA) are small, non‐coding RNA molecules that have been linked with immunity through regulating/modulating gene expression. A role for these molecules in T‐cell and B‐cell development and function has been well established. An increasing body of literature now highlights the importance of specific miRNA in dendritic cell (DC) development as well as their maturation process, antigen presentation capacity and cytokine release. Given the unique role of DC within the immune system, linking the innate and adaptive immune responses, understanding how specific miRNA affect DC function is of importance for understanding disease. In this review we summarize recent developments in miRNA and DC research, highlighting the requirement of miRNA in DC lineage commitment from bone marrow progenitors and for the development of subsets such as plasmacytoid DC and conventional DC. In addition, we discuss how infections and tumours modulate miRNA expression and consequently DC function.

Expression of a chimeric antigen receptor specific for donor HLA class I enhances the potency of human regulatory T cells in preventing human skin transplant rejection

Regulatory T cell (Treg) therapy using recipient‐derived Tregs expanded ex vivo is currently being investigated clinically by us and others as a means of reducing allograft rejection following organ transplantation. Data from animal models has demonstrated that adoptive transfer of allospecific Tregs offers greater protection from graft rejection compared to polyclonal Tregs. Chimeric antigen receptors (CAR) are clinically translatable synthetic fusion proteins that can redirect the specificity of T cells toward designated antigens. We used CAR technology to redirect human polyclonal Tregs toward donor‐MHC class I molecules, which are ubiquitously expressed in allografts. Two novel HLA‐A2‐specific CARs were engineered: one comprising a CD28‐CD3ζ signaling domain (CAR) and one lacking an intracellular signaling domain (ΔCAR). CAR Tregs were specifically activated and significantly more suppressive than polyclonal or ΔCAR Tregs in the presence of HLA‐A2, without eliciting cytotoxic activity. Furthermore, CAR and ΔCAR Tregs preferentially transmigrated across HLA‐A2‐expressing endothelial cell monolayers. In a human skin xenograft transplant model, adoptive transfer of CAR Tregs alleviated the alloimmune‐mediated skin injury caused by transferring allogeneic peripheral blood mononuclear cells more effectively than polyclonal Tregs. Our results demonstrated that the use of CAR technology is a clinically applicable refinement of Treg therapy for organ transplantation.

Regulatory T Cell-Derived Exosomes: Possible Therapeutic and Diagnostic Tools in Transplantation

Exosomes are extracellular vesicles released by many cells of the body. These small vesicles play an important part in intercellular communication both in the local environment and systemically, facilitating in the transfer of proteins, cytokines as well as miRNA between cells. The observation that exosomes isolated from immune cells such as dendritic cells (DCs) modulate the immune response has paved the way for these structures to be considered as potential immunotherapeutic reagents. Indeed, clinical trials using DC derived exosomes to facilitate immune responses to specific cancer antigens are now underway. Exosomes can also have a negative effect on the immune response and exosomes isolated from regulatory T cells (Tregs) and other subsets of T cells have been shown to have immune suppressive capacities. Here, we review what is currently known about Treg derived exosomes and their contribution to immune regulation, as well as highlighting their possible therapeutic potential for preventing graft rejection, and use as diagnostic tools to assess transplant outcome.

Antigen-specificity using chimeric antigen receptors: the future of regulatory T-cell therapy?

Adoptive regulatory T-cell (Treg) therapy using autologous Tregs expandedex vivois a promising therapeutic approach which is currently being investigated clinically as a means of treating various autoimmune diseases and transplant rejection. Despite this, early results have highlighted the need for potent Tregs to yield a substantial clinical advantage. One way to achieve this is to create antigen-specific Tregs which have been shown in pre-clinical animal models to have an increased potency at suppressing undesired immune responses, compared to polyclonal Tregs. This mini review outlines where Treg therapy currently stands and discusses the approaches which may be taken to generate antigen-specific Tregs, including the potential use of chimeric antigen receptors (CARs), for future clinical trials.

Regulatory T cells: tolerance induction in solid organ transplantation

The concept of regulatory T cell (Treg) therapy in transplantation is now a reality. Significant advances in science and technology have enabled us to isolate human Tregs, expand them to clinically relevant numbers and infuse them into human transplant recipients. With several Phase I/II trials under way investigating Treg safety and efficacy it is now more crucial than ever to understand their complex biology. However, our journey is by no means complete; results from these trials will undoubtedly provoke both further knowledge and enquiry which, alongside evolving science, will continue to drive the optimization of Treg therapy in the pursuit of transplantation tolerance. In this review we will summarize current knowledge of Treg biology, explore novel technologies in the setting of Treg immunotherapy and address key prerequisites surrounding the clinical application of Tregs in transplantation.

What Is Direct Allorecognition

A bstractDirect allorecognition is the process by which donor-derived major histocompatibility complex (MHC)-peptide complexes, typically presented by donor-derived ‘passenger’ dendritic cells, are recognised directly by recipient T cells. In this review, we discuss the two principle theories which have been proposed to explain why individuals possess a high-precursor frequency of T cells with direct allospecificity and how self-restricted T cells recognise allogeneic MHC-peptide complexes. These theories, both of which are supported by functional and structural data, suggest that T cells recognising allogeneic MHC-peptide complexes focus either on the allopeptides bound to the allo-MHC molecules or the allo-MHC molecules themselves. We discuss how direct alloimmune responses may be sustained long term, the consequences of this for graft outcome and highlight novel strategies which are currently being investigated as a potential means of reducing rejection mediated through this pathway.

Reduced Tcr Signaling Contributes to Impaired Th17 Responses in Tolerant Kidney Transplant Recipients

Background The development of spontaneous kidney transplant tolerance has been associated with numerous B cell–related immune alterations. We have previously shown that tolerant recipients exhibit reduced B-cell receptor signalling and higher IL-10 production than healthy volunteers. However, it is unclear whether cluster of differentiation (CD)4+ T cells from tolerant recipients also display an anti-inflammatory profile that could contribute to graft maintenance. Methods CD4+ T cells were isolated from kidney transplant recipients who were identified as being tolerant recipients, patients with chronic rejection or healthy volunteers. CD4+ T cells from the 3 groups were compared in terms of their gene expression profile, phenotype, and functionally upon activation. Results Gene expression analysis of transcription factors and signalling proteins, in addition to surface proteins expression and cytokine production, revealed that tolerant recipients possessed fewer Th17 cells and exhibited reduced Th17 responses, relative to patients with chronic rejection or healthy volunteers. Furthermore, impaired T-cell receptor signalling and altered cytokine cooperation by monocytes contributed to the development of Th17 cells in tolerant recipients. Conclusions These data suggest that defective proinflammatory Th17 responses may contribute to the prolonged graft survival and stable graft function, which is observed in tolerant recipients in the absence of immunosuppressive agents.

Regulatory T cell-derived extracellular vesicles modify dendritic cell function

Regulatory T cells (Treg) are a subpopulation of T cells that maintain tolerance to self and limit other immune responses. They achieve this through different mechanisms including the release of extracellular vesicles (EVs) such as exosomes as shown by us, and others. One of the ways that Treg derived EVs inhibit target cells such as effector T cells is via the transfer of miRNA. Another key target for the immunoregulatory function of Tregs is the dendritic cells (DCs). In this study we demonstrate directly, and for the first time, that miRNAs are transferred from Tregs to DCs via Treg derived EVs. In particular two miRNAs, namely miR-150-5p and miR-142-3p, were increased in DCs following their interaction with Tregs and Treg derived exosomes. One of the consequences for DCs following the acquisition of miRNAs contained in Treg derived EVs was the induction of a tolerogenic phenotype in these cells, with increased IL-10 and decreased IL-6 production being observed following LPS stimulation. Altogether our findings provide data to support the idea that intercellular transfer of miRNAs via EVs may be a novel mechanism by which Tregs regulate DC function and could represent a mechanism to inhibit immune reactions in tissues.

Human retinoic acid–regulated CD161+ regulatory T cells support wound repair in intestinal mucosa

Repair of tissue damaged during inflammatory processes is key to the return of local homeostasis and restoration of epithelial integrity. Here we describe CD161+ regulatory T (Treg) cells as a distinct, highly suppressive population of Treg cells that mediate wound healing. These Treg cells were enriched in intestinal lamina propria, particularly in Crohn’s disease. CD161+ Treg cells had an all-trans retinoic acid (ATRA)-regulated gene signature, and CD161 expression on Treg cells was induced by ATRA, which directly regulated the CD161 gene. CD161 was co-stimulatory, and ligation with the T cell antigen receptor induced cytokines that accelerated the wound healing of intestinal epithelial cells. We identified a transcription-factor network, including BACH2, RORγt, FOSL2, AP-1 and RUNX1, that controlled expression of the wound-healing program, and found a CD161+ Treg cell signature in Crohn’s disease mucosa associated with reduced inflammation. These findings identify CD161+ Treg cells as a population involved in controlling the balance between inflammation and epithelial barrier healing in the gut.Treg cells are essential for enforcing peripheral tolerance but can also influence tissue regeneration. Afzali and colleagues use high-dimensional analysis to describe a distinct population of CD161+ human Treg cells involved in wound healing of the intestinal mucosa.