measurement-of-t-cell-alloreactivity-using-imaging-flow-cytometry

Measurement of T Cell Alloreactivity Using Imaging Flow Cytometry

The measurement of immunological reactivity to donor antigens in transplant recipients is likely to be crucial for the successful reduction or withdrawal ...

University of Oxford

Composite tissue transplantation effectively reconstructs the most complex defects, but its use is limited because of harmful immunosuppression and the high susceptibility of skin to rejection. Development of tolerance is an ideal solution, and protocols using regulatory T cells (Tregs) to achieve this have been promising in experimental animal models. The aim of this study was to investigate the ability of human Tregs to regulate immune responses to a human skin allograft in vivo.

Ex vivo-expanded human regulatory T cells prevent the rejection of skin allografts in a humanized mouse model.

Leukocyte depletion at the time of transplantation with alemtuzumab (Campath-1H) has been demonstrated to be a potential strategy for reducing long-term exposure to immunosuppressive drugs. Although the impact of alemtuzumab treatment on the immune system has been explored, the effects of long-term immunosuppressive therapy in alemtuzumab-treated patients still need to be elucidated.

Th17 cells in alemtuzumab-treated patients: the effect of long-term maintenance immunosuppressive therapy.

Immune regulation is fundamental to any immune response to ensure that it is appropriate for the perceived threat to the host. Following cell and organ transplantation, it is essential to control both the innate immune response triggered by the injured tissue and the adaptive immune response stimulated by mismatched donor and recipient histocompatibility antigens to enable the transplant to survive and function. Here, we discuss the leukocyte populations that can promote immune tolerance after cell or solid-organ transplantation. Such populations include regulatory T cells, B cells and macrophages, as well as myeloid-derived suppressor cells, dendritic cells and mesenchymal stromal cells. We consider the potential of these regulatory immune cells to develop and function in transplant recipients and their potential use as cellular therapies to promote long-term graft function.

Regulatory immune cells in transplantation.

Transplant arteriosclerosis (TA) restricts long-term survival of heart transplant recipients. Although the role of monocyte/macrophages is well established in native atherosclerosis, it has been studied to a much lesser extent in TA. Plasma cholesterol is the most important non-immunologic risk factor for development of TA but the underlying mechanisms are largely unknown. We hypothesized that monocyte/macrophages might play an important role in the pathogenesis of TA under hyperlipidemic conditions.

Inflammatory Ly-6C(hi) monocytes play an important role in the development of severe transplant arteriosclerosis in hyperlipidemic recipients.

Conversion to sirolimus from calcineurin inhibitor- (CNI), azathioprine- (AZA) and mycophenolate-based regimens reduces the risk of development of squamous cell carcinoma of the skin (SCC) in kidney transplant recipients (KTRs). Sirolimus conversion may also be protective by permitting beneficial changes in immune phenotype. It is not known how sirolimus will affect immune phenotype in KTRs with SCC.

Conversion to sirolimus in kidney transplant recipients with squamous cell cancer and changes in immune phenotype.

Regulatory T cells (Treg) are potentially a useful therapeutic option for the treatment of immunopathological conditions including graft-versus-host disease. Umbilical cord blood (UCB) offers certain advantages over adult peripheral blood (APB) as a source of Treg for cellular therapy but yields far fewer Treg per unit. Pooling of Treg from multiple donors may overcome this challenge.

Multiple unit pooled umbilical cord blood is a viable source of therapeutic regulatory T cells.

Regulatory T cell (Treg) therapy for immune modulation is a promising therapeutic strategy for the treatment and prevention of autoimmune disease and graft-versus-host disease (GvHD) after bone marrow transplantation. However, Treg are heterogeneous and express a variety of chemokine receptor molecules. The optimal subpopulation of Treg for therapeutic use may vary according to the pathological target. Indeed, clinical trials of Treg for the prevention of GvHD where the skin is a major target of the anti-host response have employed Treg derived from a variety of different sources. We postulated that for the effective treatment of GvHD-related skin pathology, Treg must be able to migrate to skin in order to regulate local alloimmune responses efficiently. To test the hypothesis that different populations of Treg display distinct efficacy in vivo based on their expression of tissue-specific homing molecules, we evaluated the activity of human Treg derived from two disparate sources in a model of human skin transplantation. Treg were derived from adult blood or cord blood and expanded in vitro. While Treg from both sources displayed similar in vitro suppressive efficacy, they exhibited marked differences in the expression of skin homing molecules. Importantly, only adult-derived Treg were able to prevent alloimmune-mediated human skin destruction in vivo, by virtue of their improved migration to skin. The presence of Treg within the skin was sufficient to prevent its alloimmune-mediated destruction. Additionally, Treg expressing the skin homing cutaneous lymphocyte antigen (CLA) were more efficient at preventing skin destruction than their CLA-deficient counterparts. Our findings highlight the importance of the careful selection of an effective subpopulation of Treg for clinical use according to the pathology of interest.

Homing of regulatory T cells to human skin is important for the prevention of alloimmune-mediated pathology in an in vivo cellular therapy model.

Human regulatory T cells (Treg) offer an attractive adjunctive therapy to reduce current reliance on lifelong, nonspecific immunosuppression after transplantation. Here, we evaluated the ability of ex vivo expanded human Treg to prevent the rejection of islets of Langerhans in a humanized mouse model and examined the mechanisms involved.

Ex vivo expanded human regulatory T cells can prolong survival of a human islet allograft in a humanized mouse model.

Organ transplantation results in the activation of both innate and adaptive immune responses to the foreign antigens. While these responses can be limited with the use of systemic immunosuppressants, the induction of regulatory cell populations may be a novel strategy for the maintenance of specific immunological unresponsiveness that can reduce the severity of the detrimental side effects of current therapies. Our group has extensively researched different regulatory T-cell induction protocols for use as cellular therapy in transplantation. In this review, we address the cellular and molecular mechanisms behind regulatory T-cell suppression and their stability following induction protocols. We further discuss the use of different hematopoietically derived regulatory cell populations, including regulatory B cells, regulatory macrophages, tolerogenic dendritic cells, and myeloid-derived suppressor cells, for the induction of transplantation tolerance in light of new clinical trials developing therapies with some of these populations.

Induction of transplantation tolerance through regulatory cells: from mice to men.

Stem cells and their differentiated progeny offer great hope for treating disease by providing an unlimited source of cells for repairing or replacing damaged tissue. Initial studies suggested that, unlike 'normal' transplants, specific characteristics of stem cells enabled them to avoid immune attack. However, recent findings have revealed that the immunogenicity of stem cells may have been underestimated. Here, we review the current understanding of the mechanisms of immune recognition associated with stem cell immunogenicity, and discuss the relevance of reprogramming and differentiation strategies used to generate cells or tissue from stem cells for implantation in eliciting an immune response. We examine the effectiveness of current strategies for minimising immune attack in light of our experience in the transplantation field and, in this context, outline important challenges moving forward.

Article	Year
Ex vivo-expanded human regulatory T cells prevent the rejection of skin allografts in a humanized mouse model. Transplantation\| PubMed ID: 21048528	2010
Th17 cells in alemtuzumab-treated patients: the effect of long-term maintenance immunosuppressive therapy. Transplantation\| PubMed ID: 21412187	2011
Regulatory immune cells in transplantation. Nature reviews. Immunology\| PubMed ID: 22627860	2012
Inflammatory Ly-6C(hi) monocytes play an important role in the development of severe transplant arteriosclerosis in hyperlipidemic recipients. Atherosclerosis\| PubMed ID: 22704806	2012
Conversion to sirolimus in kidney transplant recipients with squamous cell cancer and changes in immune phenotype. Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association\| PubMed ID: 23223314	2013
Multiple unit pooled umbilical cord blood is a viable source of therapeutic regulatory T cells. Transplantation\| PubMed ID: 23263503	2013
Homing of regulatory T cells to human skin is important for the prevention of alloimmune-mediated pathology in an in vivo cellular therapy model. PloS one\| PubMed ID: 23300911	2012
Ex vivo expanded human regulatory T cells can prolong survival of a human islet allograft in a humanized mouse model. Transplantation\| PubMed ID: 23917725	2013
Induction of transplantation tolerance through regulatory cells: from mice to men. Immunological reviews\| PubMed ID: 24517428	2014
Understanding Stem Cell Immunogenicity in Therapeutic Applications. Trends in immunology\| PubMed ID: 26687737	2016

Joanna Hester

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