Path to clinical transplantation tolerance and prevention of graft-versus-host disease

CD4+CD25+ T regulatory cells in renal transplantation

The immune response to an allograft activates lymphocytes with the capacity to cause rejection. Activation of CD4+CD25+Foxp3+T regulatory cells (Treg) can down-regulate allograft rejection and can induce immune tolerance to the allograft. Treg represent <10% of peripheral CD4+T cells and do not markedly increase in tolerant hosts. CD4+CD25+Foxp3+T cells include both resting and activated Treg that can be distinguished by several markers, many of which are also expressed by effector T cells. More detailed characterization of Treg to identify increased activated antigen-specific Treg may allow reduction of non-specific immunosuppression. Natural thymus derived resting Treg (tTreg) are CD4+CD25+Foxp3+T cells and only partially inhibit alloantigen presenting cell activation of effector cells. Cytokines produced by activated effector cells activate these tTreg to more potent alloantigen-activated Treg that may promote a state of operational tolerance. Activated Treg can be distinguished by several molecules they are induced to express, or whose expression they have suppressed. These include CD45RA/RO, cytokine receptors, chemokine receptors that alter pathways of migration and transcription factors, cytokines and suppression mediating molecules. As the total Treg population does not increase in operational tolerance, it is the activated Treg which may be the most informative to monitor. Here we review the methods used to monitor peripheral Treg, the effect of immunosuppressive regimens on Treg, and correlations with clinical outcomes such as graft survival and rejection. Experimental therapies involving ex vivo Treg expansion and administration in renal transplantation are not reviewed.

Attenuation of graft-versus-host-disease in NOD scid IL-2Rγ(-/-) (NSG) mice by ex vivo modulation of human CD4(+) T cells

NOD.Cg-Prkdc(scid) IL-2rg(tm1Wjl) /SzJ (NSG) mice are a valuable tool for studying Graft-versus-Host-Disease (GvHD) induced by human immune cells. We used a model of acute GvHD by transfer of human peripheral blood mononuclear cells (PBMCs) into NSG mice. The severity of GvHD was reflected by weight loss and was associated with engraftment of human cells and the expansion of leukocytes, particularly granulocytes and monocytes. Pre-treatment of PBMCs with the anti-human CD4 antibody MAX.16H5 IgG1 or IgG4 attenuated GvHD. The transplantation of 2 × 10(7) PBMCs without anti-human CD4 pre-treatment induced a severe GvHD (0% survival). In animals receiving 2 × 10(7) PBMCs pre-incubated with MAX.16H5 IgG1 or IgG4, GvHD development was reduced and survival was increased. Immune reconstitution was measured by flow cytometry and confirmed for human leukocytes (CD45), CD3(+) /CD8(+) cytotoxic T cells and CD3(+) /CD4(+) T helper cells. Human B cells (CD19) and monocytes (CD14) could not be detected. Histopathological analysis (TUNEL assay) of the gut of recipient animals showed significantly less apoptotic crypt cells in animals receiving a MAX.16H5 IgG1 pre-incubated graft. These findings indicate that pre-incubation of an allogeneic graft with an anti-human CD4 antibody may decrease the frequency and severity of GvHD after hematopoietic stem cell transplantation (HSCT) and the need of conventional immunosuppressive drugs. Moreover, this approach most probably provides a safer HSCT that must be confirmed in appropriate clinical trials in the future. © 2016 International Society for Advancement of Cytometry.

Controlling the burn and fueling the fire: defining the role for the alarmin interleukin-33 in alloimmunity

PURPOSE OF REVIEW

The purpose of this review is to provide a general update on recent developments in the immunobiology of IL-33 and IL-33-targeted immune cells. We also discuss emerging concepts regarding the potential role IL-33 appears to play in altering alloimmune responses mediating host-versus-graft and graft-versus-host alloresponses.

RECENT FINDINGS

Stromal cells and leukocytes display regulated expression of IL-33 and may actively or passively secrete this pleotropic cytokine. Type 2 innate lymphoid cells and a large proportion of tissue resident regulatory T cells (Treg) express membrane-bound suppressor of tumorigenicity 2 (ST2), the IL-33 receptor. Although Treg are appreciated suppressors of the inflammatory function of immune cells, both type 2 innate lymphoid cells and tissue resident Treg could play key roles in tissue repair and homeostasis. The functions of IL-33 in transplantation are poorly understood. However, like other disease models, the functions of IL-33 in alloimmunity appear to be quite pleiotropic. IL-33 is associated with immune regulation and graft protection in cardiac transplant settings. Yet, it is highly proinflammatory and stimulates lethal graft-versus-host disease through its capacity to stimulate type 1 immunity.

SUMMARY

Intensive studies on IL-33/ST2 signaling pathways and ST2 cell populations in solid organ and cell transplantation are warranted. A better understanding of this important pathway will provide promising therapeutic targets controlling pathogenic alloimmune responses, as well as potentially facilitating the function of regulatory and reparative immune cells posttransplantation.

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

The early history of Stanford Immunology

From its 1960 beginnings in a pair of windowless Genetics Department laboratories under the Stanford Medical School Dean's Office to its current broad-based program, which joins faculty members from departments across the Medical School, the Stanford Immunology Program has played a central role in shaping both basic and clinical immunology thinking. In this article, we tell the story of the beginnings of this odyssey in a reminiscence-based format that brings the flavor of the time in the words of people who lived and built the history.