Pulmonary and esophageal function in lung transplantation: Fundamental principles and clinical application

The lungs and esophagus have a close anatomical and physiological relationship. Over the years, reflux-induced pulmonary injury has gained wider recognition, but the full effects of pulmonary disease on esophageal function are still unknown. Intrathoracic pressure dynamics potentially affect esophageal function, especially in patients with end-stage lung disease, both obstructive and restrictive. Lung transplantation is the only viable option for patients with end-stage pulmonary disease and has provided us with a unique opportunity to study these effects as transplantation restores the intrathoracic environment. Esophageal and foregut functional testing before and after transplantation provide insights into the pathophysiology of the foregut-pulmonary axis, such as how underlying pulmonary disease and intrathoracic pressure changes affect esophageal physiology. This review summarizes the available literature and shares the research experience of a lung transplant center, covering topics such as pre- and posttransplant foregut function, esophageal motility in lung transplant recipients, immune-mediated mechanisms of graft rejection associated with gastroesophageal reflux, and the role of antireflux surgery in this population.

Mast cell-mediated mechanistic pathways in organ transplantation

Adaptive immunity has gained importance in transplant immunology for years, based on models in which T-cells orchestrate the immune responses during rejection. Most recently, researches revealed that innate immune cells, including mast cells (MCs) also play a pivotal role in allograft rejection. MC mediated immunoregulatory responses influence the innate and adaptive immune responses. Their capability to produce an array of both pro-inflammatory and anti-inflammatory mediators, expressing a wide range of costimulatory molecules in addition to acting as antigen-presenting cells (APCs), make them effective immune cells far beyond their classical role as primary orchestrator cells of allergy. Activated regulatory Tcells (Treg) cells contribute to MC recruitment into grafts by releasing interleukin (IL)-9. Tregs are capable of stabilizing MCs and suppressing IgE mediated degranulation through interaction of Treg expressing OX40 with MCs expressing OX40L. MCs in turn release transforming growth factor (TGF)-β and IL-10 which possess suppressive properties. Thus, these cells can suppress the proliferation of T-cells and support the generation of Tregs. MCs in addition to orchestrating immune responses in grafts by cell-to-cell interactions with variety of immune cells, cause histologic changes, mainly fibrosis by releasing mediators such as histamine, fibroblast growth factor-2 (FGF-2), TGF-β, chymase, and cathepsin G. The role of MCs in transplant rejection remains controversial. The accumulation of MCs in rejected grafts suggests that they play a role in preventing graft tolerance, and contribute to the progression of chronic rejection of allografts. However, high expression of MC-related gene products in tolerant grafts and their known interaction with Tregs on the other hand, support the notion that they are an integral component in achieving peripheral tolerance.

Preclinical and clinical studies for transplant tolerance via the mixed chimerism approach

Based upon observations in murine models, we have developed protocols to induce renal allograft tolerance by combined kidney and bone marrow transplantation (CKBMT) in non-human primates (NHP) and in humans. Induction of persistent mixed chimerism has proved to be extremely difficult in major histocompatibility complex (MHC)-mismatched primates, with detectable chimerism typically disappearing within 30-60 days. Nevertheless, in MHC mismatched NHP, long-term immunosuppression-free renal allograft survival has been achieved reproducibly, using a non-myeloablative conditioning approach that has also been successfully extended to human kidney transplant recipients. CKBMT has also been applied to the patients with end stage renal disease with hematologic malignancies. Renal allograft tolerance and long-term remission of myeloma have been achieved by transient mixed or persistent full chimerism. This review summarizes the current status of preclinical and clinical studies for renal and non-renal allograft tolerance induction by CKBMT. Improving the consistency of tolerance induction with less morbidity, extending this approach to deceased donor transplantation and inducing tolerance of non-renal transplants, are critical next steps for bringing this strategy to a wider range of clinical applications.

Blimp-1 prolongs allograft survival without regimen via influencing T cell development in favor of regulatory T cells while suppressing Th1

BACKGROUND

B lymphocyte-induced maturation protein 1 (Blimp-1) transcription factor is expressed in multiple cell lineages and in particular, T cells. However, the role of Blimp-1 in T cell-mediated allograft tolerance is still unknown.

METHODS

This study is the first to investigate transplanted skin allograft survival using transgenic (Tg) mice with T cell overexpression of Blimp-1.

RESULTS

Without any immunosuppression, fully MHC-mismatched skin allografts on Tg(+) mice had a significantly prolonged survival rate and partial tolerance at 90 days. Allograft lymphocytic infiltration was decreased in Tg(+) mice and a dampened donor-stimulated alloimmune response was seen. An absolute cell number ratio of inflammatory Th1 and Th17 cells against anti-inflammatory regulatory T (Treg) and IL-10-producing T cells, as well as cytolytic proteins, were significantly decreased in lymphoid organs and allograft. Blimp-1 transgenic T cells displayed an increased Treg differentiation capability and enhanced suppression of T cell proliferation. Overexpression of Blimp-1 in T cells promoted the formation of an anti-inflammatory cell-cytokine composition, both systemically and locally via transcription factor modulation such as T-bet downregulation and FoxP3 upregulation.

DISCUSSION

As such, allograft survival was made possible due to Th1 suppression and Treg amplification with the creation of an 'allograft protective microenvironment'.

Stromal Cell-Derived Factor-1 Mediates Cardiac Allograft Tolerance Induced by Human Endometrial Regenerative Cell-Based Therapy

Endometrial regenerative cells (ERCs) are mesenchymal-like stromal cells, and their therapeutic potential has been tested in the prevention of renal ischemic reperfusion injury, acute liver injury, ulcerative colitis, and immunosuppression. However, their potential in the induction of transplant tolerance has not been investigated. The present study was undertaken to investigate the efficacy of ERCs in inducing cardiac allograft tolerance and the function of stromal cell-derived factor-1 (SDF-1) in the ERC-mediated immunoregulation. The inhibitory efficacy of human ERCs in the presence or absence of rapamycin was examined in both mouse cardiac allograft models between BALB/c (H-2^d ) donors and C57BL/6 (H-2^b ) recipients and in vitro cocultured splenocytes. AMD3100 was used to inhibit the function of SDF-1. Intragraft antibody (IgG and IgM) deposition and immune cell (CD4⁺ and CD8⁺ ) infiltration were measured by immunohistochemical staining, and splenocyte phenotypes were determined by fluorescence-activated cell sorting analysis. The results showed that ERC-based therapy induced donor-specific allograft tolerance, and functionally inhibiting SDF-1 resulted in severe allograft rejection. The negative effects of inhibiting SDF-1 on allograft survival were correlated with increased levels of intragraft antibodies and infiltrating immune cells, and also with reduced levels of regulatory immune cells including MHC class II^low CD86^low CD40^low dendritic cells, CD68⁺ CD206⁺ macrophages, CD4⁺ CD25⁺ Foxp3⁺ T cells, and CD1d^high CD5^high CD83^low IL-10^high B cells both in vivo and in vitro. These data showed that human ERC-based therapy induces cardiac allograft tolerance in mice, which is associated with SDF-1 activity, suggesting that SDF-1 mediates the immunosuppression of ERC-based therapy for the induction of transplant tolerance. Stem Cells Translational Medicine 2017;6:1997-2008.

Indoleamine 2,3-dioxygenase inhibition alters the non-coding RNA transcriptome following renal ischemia-reperfusion injury

BACKGROUND

Indoleamine 2,3 dioxygenase (IDO) degrades the essential amino acid tryptophan and has been shown to minimize rejection in animal models of renal transplantation. Ischemia-reperfusion injury (IRI) is unavoidable in renal transplantation and correlates with shorter graft survival times. Despite its favorable effects on rejection, there is evidence that IDO may facilitate renal IRI. Differentiating the negative impact of IDO on IRI from its pro-tolerant effects in allograft rejection is of clinical relevance. In these studies we hypothesized that constitutive IDO activity may influence renal genes associated with recovery from IRI, and that IDO inhibition may unmask these effects.

METHODS

We examined the renal transcriptome in a rat model of IRI with and without IDO inhibition with 1-methyl-d-tryptophan (1-MT), and assessed for alterations in the gene expression signature.

RESULTS

These studies demonstrated that during recovery from renal IRI, pre-treatment with 1-MT alleviated alterations in 105 coding sequences associated with IRI, and in turn triggered new changes in 66 non-coding transcripts, the majority of which were represented by small nucleolar RNA.

CONCLUSION

These results suggest a biologic role for non-coding, IDO-dependent genes in regulating the early response to IRI.

Harnessing regulatory T cells for clinical use in transplantation: the end of the beginning

Owing to the adverse effects of immunosuppression and an inability to prevent chronic rejection, there is a pressing need for alternative strategies to control alloimmunity. In three decades, regulatory T cells (Tregs) have evolved from a hypothetical mediator of adoptively transferred tolerance to a well-defined population that can be expanded ex vivo and returned safely to patients in clinical trials. Herein, we review the historical developments that have permitted these advances and the current status of clinical trials examining Tregs as a cellular therapy in transplantation. We conclude by discussing the critical unanswered questions that face this field in the coming years.