Cardiac fibrosis, associated with a decreased extent of microvasculature and with disruption of normal myocardial structures, results from excessive deposition of extracellular matrix, which is mediated by the recruitment of fibroblasts. The source of these fibroblasts is unclear and specific anti-fibrotic therapies are not currently available. Here we show that cardiac fibrosis is associated with the emergence of fibroblasts originating from endothelial cells, suggesting an endothelial-mesenchymal transition (EndMT) similar to events that occur during formation of the atrioventricular cushion in the embryonic heart. Transforming growth factor-beta1 (TGF-beta1) induced endothelial cells to undergo EndMT, whereas bone morphogenic protein 7 (BMP-7) preserved the endothelial phenotype. The systemic administration of recombinant human BMP-7 (rhBMP-7) significantly inhibited EndMT and the progression of cardiac fibrosis in mouse models of pressure overload and chronic allograft rejection. Our findings show that EndMT contributes to the progression of cardiac fibrosis and that rhBMP-7 can be used to inhibit EndMT and to intervene in the progression of chronic heart disease associated with fibrosis.

The ability to replace organs and tissues on demand could save or improve millions of lives each year globally and create public health benefits on par with curing cancer. Unmet needs for organ and tissue preservation place enormous logistical limitations on transplantation, regenerative medicine, drug discovery, and a variety of rapidly advancing areas spanning biomedicine. A growing coalition of researchers, clinicians, advocacy organizations, academic institutions, and other stakeholders has assembled to address the unmet need for preservation advances, outlining remaining challenges and identifying areas of underinvestment and untapped opportunities. Meanwhile, recent discoveries provide proofs of principle for breakthroughs in a family of research areas surrounding biopreservation. These developments indicate that a new paradigm, integrating multiple existing preservation approaches and new technologies that have flourished in the past 10 years, could transform preservation research. Capitalizing on these opportunities will require engagement across many research areas and stakeholder groups. A coordinated effort is needed to expedite preservation advances that can transform several areas of medicine and medical science.

The presence of preexisting (memory) or de novo donor-specific HLA antibodies (DSAs) is a known barrier to successful long-term organ transplantation. Yet, despite the fact that laboratory tools and our understanding of histocompatibility have advanced significantly in recent years, the criteria to define presence of a DSA and assign a level of risk for a given DSA vary markedly between centers. A collaborative effort between the American Society for Histocompatibility and Immunogenetics and the American Society of Transplantation provided the logistical support for generating a dedicated multidisciplinary working group, which included experts in histocompatibility as well as kidney, liver, heart, and lung transplantation. The goals were to perform a critical review of biologically driven, state-of-the-art, clinical diagnostics literature and to provide clinical practice recommendations based on expert assessment of quality and strength of evidence. The results of the Sensitization in Transplantation: Assessment of Risk (STAR) meeting are summarized here, providing recommendations on the definition and utilization of HLA diagnostic testing, and a framework for clinical assessment of risk for a memory or a primary alloimmune response. The definitions, recommendations, risk framework, and highlighted gaps in knowledge are intended to spur research that will inform the next STAR Working Group meeting in 2019.

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Background-Allograft vasculopathy is a major limiting factor in the long-term success of cardiac transplantation. T cells play a critical role in initiation of cardiac allograft rejection and allograft vasculopathy. The negative T-cell costimulatory pathway PD-1:PDL1/PDL2 (programmed death-1:programmed death ligand-1/2) plays an important role in regulating alloimmune responses. We investigated the role of recipient versus donor PD-1 ligands in the pathogenesis of allograft rejection with emphasis on the role of tissue expression in regulating this alloimmune response in vivo. Methods and Results-We used established major histocompatibility complex class II-and class I-mismatched models of vascularized cardiac allograft rejection, blocking anti-PDL1 and anti-PDL2 antibodies, and PDL1-and PDL2-deficient mice (as donors or recipients) to study the role of the PD-1:PDL1/PDL2 pathway in chronic rejection. We also used PDL1-deficient and wild-type mice and bone marrow transplantation to generate chimeric animals that express PDL1 exclusively on either hematopoietic or parenchymal cells. PDL1 but not PDL2 blockade significantly accelerated cardiac allograft rejection in the bm12-into-B6 and B6-into-bm12 models. Although wild-type cardiac allografts survived long term, PDL1 Ϫ/Ϫ donor hearts transplanted into wild-type bm12 mice exhibited accelerated rejection and vasculopathy associated with enhanced recipient T-cell alloreactivity. Interestingly, PDL1Ϫ/Ϫ recipients did not exhibit an accelerated tempo of cardiac allograft rejection. Using chimeric animals as donors, we show that PDL1 expression on cardiac tissue alone significantly prolonged graft survival compared with full PDL1 Ϫ/Ϫ donor grafts in transplanted wild-type recipients. Conclusions-This is the first report to demonstrate that expression of the negative costimulatory molecule PDL1 on donor cardiac tissue regulates recipient alloimmune responses, allograft rejection, and vasculopathy. (Circulation. 2008;117: 660-669.)

One injection of anti-CD154 or CTLA4Ig overcomes the need for TI or prolonged host TCD in a preclinical model for the induction of mixed chimerism and deletional tolerance and thus further decreases the toxicity of this protocol. Achievement of tolerance with conditioning given over 24 hr suggests applicability to cadaveric organ transplantation.

We studied T-cell clones generated from grafts of rejecting and tolerant animals and investigated the regulatory function of Th2 clones in vitro and in vivo. To prevent allograft rejection, we treated LEW strain recipient rats of WF strain kidney grafts with CTLA4Ig to block CD28-B7 costimulation. We then isolated epitope-specific T-cell clones from the engrafted tissue, using a donor-derived immunodominant class II MHC allopeptide presented by recipient antigen-presenting cells. Acutely rejected tissue from untreated animals yielded self-restricted, allopeptide-specific T-cell clones that produced IFN-γ, whereas clones from tolerant animals produced IL-4 and IL-10. Adoptive transfer into naive recipients of Th1 clones, but not Th2 clones, induced alloantigen-specific delayed-type hypersensitivity (DTH) responses. In addition, Th2 clones suppressed DTH responses mediated by Th1 clones in vivo and blocked Th1 cell proliferation and IFN-γ production in vitro. A pilot human study showed that HLA-DR allopeptide-specific T-cell clones generated from patients with chronic rejection secrete Th1 cytokines, whereas those from patients with stable graft function produce Th2 cytokines in response to donor-specific HLA-DR allopeptides. We suggest that self-restricted alloantigen-specific Th2 clones may regulate the alloimmune responses and promote long-term allograft survival and tolerance. See related Commentary on pages 797-798rats undergoing acute vascularized allograft rejection express a restricted TCR Vβ repertoire and transfer DTH responses in vivo (16). In this study, we compared for the first time, to our knowledge, the functions of self-restricted alloreactive T-cell clones generated from grafts of rejecting and tolerant animals and analyzed the putative regulatory functions of Th2 clones in vitro and in vivo. Results of a pilot study in kidney transplant recipients with chronic rejection or stable graft function establish the biological relevance of our animal studies in humans. Our results confirm the regulatory functions of alloreactive Th2 clones and provide an invaluable tool for the study of the functions of Th1 and Th2 clones in acute/chronic allograft rejection and tolerance in vivo. MethodsAnimals. Inbred 200-250 g male Lewis (LEW; RT1 l ) rats were used as recipients and Wistar Furth (WF; RT1 u ) rats served as donors. They were purchased from Harlan Sprague-Dawley Inc. (Indianapolis, Indiana, USA).Rat kidney transplantation. LEW rats underwent bilateral nephrectomies and received heterotopic MHCincompatible WF renal allografts. For the purpose of this study, we used two groups of animals. The first group was unmodified and the rejecting graft was harvested on day 7. The second group was treated with a single injection of human cytotoxic lymphocyte activation factor 4 (CTLA4Ig; Bristol Myers Squibb Co., Princeton, New Jersey, USA) on day 2 after transplant and the graft was harvested after 100 days. This protocol of CTLA4Ig administration has previously been shown by Sayegh's group to induce long-term a...

Despite high rates of early rejection, desensitization in living-kidney transplantation results in acceptable 5-year patient and graft survival rates.