Modulation of tissue-specific immune response to cardiac myosin can prolong survival of allogeneic heart transplants

Damage-Associated Molecular Patterns in Myocardial Infarction and Heart Transplantation: The Road to Translational Success

In the setting of myocardial infarction (MI), ischemia reperfusion injury (IRI) occurs due to occlusion (ischemia) and subsequent re-establishment of blood flow (reperfusion) of a coronary artery. A similar phenomenon is observed in heart transplantation (HTx) when, after cold storage, the donor heart is connected to the recipient's circulation. Although reperfusion is essential for the survival of cardiomyocytes, it paradoxically leads to additional myocardial damage in experimental MI and HTx models. Damage (or danger)-associated molecular patterns (DAMPs) are endogenous molecules released after cellular damage or stress such as myocardial IRI. DAMPs activate pattern recognition receptors (PRRs), and set in motion a complex signaling cascade resulting in the release of cytokines and a profound inflammatory reaction. This inflammatory response is thought to function as a double-edged sword. Although it enables removal of cell debris and promotes wound healing, DAMP mediated signalling can also exacerbate the inflammatory state in a disproportional matter, thereby leading to additional tissue damage. Upon MI, this leads to expansion of the infarcted area and deterioration of cardiac function in preclinical models. Eventually this culminates in adverse myocardial remodeling; a process that leads to increased myocardial fibrosis, gradual further loss of cardiomyocytes, left ventricular dilation and heart failure. Upon HTx, DAMPs aggravate ischemic damage, which results in more pronounced reperfusion injury that impacts cardiac function and increases the occurrence of primary graft dysfunction and graft rejection via cytokine release, cardiac edema, enhanced myocardial/endothelial damage and allograft fibrosis. Therapies targeting DAMPs or PRRs have predominantly been investigated in experimental models and are potentially cardioprotective. To date, however, none of these interventions have reached the clinical arena. In this review we summarize the current evidence of involvement of DAMPs and PRRs in the inflammatory response after MI and HTx. Furthermore, we will discuss various current therapeutic approaches targeting this complex interplay and provide possible reasons why clinical translation still fails.

Lung Injury and Loss of Regulatory T Cells Primes for Lung-Restricted Autoimmunity

Lung transplantation is a life-saving therapy for several end-stage lung diseases. However, lung allografts suffer from the lowest survival rate predominantly due to rejection. The pathogenesis of alloimmunity and its role in allograft rejection has been extensively studied and multiple approaches have been described to induce tolerance. However, in the context of lung transplantation, dysregulation of mechanisms, which maintain tolerance against self-antigens, can lead to lung-restricted autoimmunity, which has been recently identified to drive the immunopathogenesis of allograft rejection. Indeed, both preexisting as well as de novo lung-restricted autoimmunity can play a major role in the development of lung allograft rejection. The three most widely studied lung-restricted self-antigens include collagen type I, collagen type V, and k-alpha 1 tubulin. In this review, we discuss the role of lung-restricted autoimmunity in the development of both early as well as late lung allograft rejection and recent literature providing insight into the development of lung-restricted autoimmunity through the dysfunction of immune mechanisms which maintain peripheral tolerance.

Exosomes expressing the self-antigens myosin and vimentin play an important role in syngeneic cardiac transplant rejection induced by antibodies to cardiac myosin

Long-term success of heart transplantation is hindered by humoral and cell-mediated immune responses. We studied preexisting antibodies to cardiac self-antigens, myosin and vimentin, and exosomes induced by antibodies to self-antigens in eliciting immune responses to cardiac grafts. After syngeneic heterotopic murine heart transplantation, rabbit anti-myosin or normal rabbit immunoglobulin was administered at day 0 or 7. Sera were collected after heartbeat cessation, cellular infiltration was analyzed, and exosomes were isolated from sera. Histopathologic examination of the controls' transplanted hearts demonstrated normal architecture, and their sera demonstrated neither antibodies to self-antigens nor exosomes expressing self-antigens. Administration of antibodies to cardiac myosin immediately posttransplantation (day 0) but not on day 7 triggered graft failure on day 7, and histopathologic examination revealed marked cellular infiltration with neutrophils and lymphocytes. Histopathologic examination of rejected hearts also demonstrated myocyte damage as sera had increased antibodies to myosin and vimentin and development of exosomes expressing self-antigens. Administration of exosomes isolated from failed grafts containing self-antigens induced graft dysfunction; exosomes isolated from stable mice did not induce graft failure. Antibodies to self-antigens can induce exosomes containing self-antigens, initiating an immune response and causing graft failure after cardiac transplantation.

Surgical perspectives regarding application of biomaterials for the management of large congenital diaphragmatic hernia defects

This review focuses on the surgical viewpoints on patch repairs in neonates with large congenital diaphragmatic hernia defects. The main focus  is on the various biomaterials that have been employed to date with regard to their source of origins, degradation properties as well as tissue integration characteristics. Further focus  is on the present knowledge on patch integration when biomaterials are placed in the diaphragmatic defect. The review will also look at the present evidence on the biomechanical characteristics of the most commonly used biomaterials and compares these materials to diaphragmatic tissue to offer more  insight on the present practice of patch repairs in large defects. Since tissue engineering and regenerative medicine has offered another dimension to diaphragmatic replacement, a detailed overview of this technology will be undertaken with regard to cell sourcing, scaffolds, in vitro versus in vivo implants as well as quality of tissue produced, to explore the limitations and the feasibility facing the scientific community in its clinical implementation of skeletal muscle-engineered tissue beyond laboratory research for diaphragmatic replacement.

Prevalence of polyreactive innate clones among graft--infiltrating B cells in human cardiac allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) has been associated with graft-infiltrating B cells, although their characteristics are still unclear. In this study we examined the frequency, localization and reactivity profile of graft-infiltrating B cells to determine their contribution to the pathophysiology of CAV.

METHODS

B cells, plasma cells and macrophages were examined by immunohistochemistry in 56 allografts with CAV, 49 native failed hearts and 25 autopsy specimens. A total of 102 B-cell clones were immortalized directly from the infiltrates of 3 fresh cardiac samples with CAV. Their secreted antibodies were assessed using enzyme-linked immunoassay and flow cytometry.

RESULTS

B-cell infiltration was observed around coronary arteries in 93% of allograft explants with CAV. Comparatively, intragraft B cells were less frequent and less dense in the intraventricular myocardium from where routine biopsies are obtained. Plasma cells and macrophages were also detected in 85% and 95% of explants, respectively. Remarkably, B-cell infiltrates were not associated with circulating donor-specific antibodies (DSA) or prior episodes of antibody-mediated rejection (AMR). Among all B-cell clones generated from 3 explants with CAV, a majority secreted natural antibodies reactive to multiple autoantigens and apoptotic cells, a characteristic of innate B cells.

CONCLUSIONS

Our study reveals a high frequency of infiltrating B cells around the coronary arteries of allografts with CAV, independent of DSA or AMR. These cells are enriched for innate B cells with a polyreactive profile. The findings shift the focus from conventional DSA-producing B cells to the potentially pathogenic polyreactive B cells in the development of clinical CAV.

Sliding Fibers: Slidable, Injectable, and Gel-like Electrospun Nanofibers as Versatile Cell Carriers

Designing biomaterial systems that can mimic fibrous, natural extracellular matrix is crucial for enhancing the efficacy of various therapeutic tools. Herein, a smart technology of three-dimensional electrospun fibers that can be injected in a minimally invasive manner was developed. Open surgery is currently the only route of administration of conventional electrospun fibers into the body. Coordinating electrospun fibers with a lubricating hydrogel produced fibrous constructs referred to as slidable, injectable, and gel-like (SLIDING) fibers. These SLIDING fibers could pass smoothly through a catheter and fill any cavity while maintaining their fibrous morphology. Their injectable features were derived from their distinctive rheological characteristics, which were presumably caused by the combinatorial effects of mobile electrospun fibers and lubricating hydrogels. The resulting injectable fibers fostered a highly favorable environment for human neural stem cell (hNSC) proliferation and neurosphere formation within the fibrous structures without compromising hNSC viability. SLIDING fibers demonstrated superior performance as cell carriers in animal stroke models subjected to the middle cerebral artery occlusion (MCAO) stroke model. In this model, SLIDING fiber application extended the survival rate of administered hNSCs by blocking microglial infiltration at the early, acute inflammatory stage. The development of SLIDING fibers will increase the clinical significance of fiber-based scaffolds in many biomedical fields and will broaden their applicability.

Autoimmune Reactivity in Graft Injury: Player or Bystander?

Organ transplantation is the only viable treatment for several end-stage organ failures. However chronic rejection prevents long-term graft survival. Traditionally this rejection was attributed to the development of alloimmunity in transplant patients. However recent evidence suggests that autoimmunity plays a larger role in chronic rejection of certain organ transplants, than alloimmunity. In this review we will focus on the history of autoimmunity in solid-organ transplantation and at look the Collagen Type V, K-α-tubulin, Vimentin, Cardiac myosin and Heat Shock Proteins as classical examples of auto-antigens in organ transplantation. We will also look at some of the recent reports looking at the mechanisms of autoimmunity and try to provide answers to some of the age-old questions in autoimmunity.

Cardiac allograft vasculopathy: a donor or recipient induced pathology?

Cardiac allograft vasculopathy (CAV) is one of the main causes of late-stage heart failure after heart transplantation. CAV is characterized by concentric luminal narrowing of the coronary arteries, but the exact pathogenesis of CAV is still not unraveled. Many researchers show evidence of an allogeneic immune response of the recipient, whereas others show contrasting results in which donor-derived cells induce an immune response against the graft. In addition, fibrosis of the neo-intima can be induced by recipient-derived circulating cells or donor-derived cells. In this review, both donor and recipient sides of the story are described to obtain better insight in the pathogenesis of CAV. Dual outcomes were found regarding the contribution of donor and recipient cells in the initiation of the immune response and the development of fibrosis during CAV. Future research could focus more on the potential synergistic interaction of donor and recipient cells leading to CAV.

Immune response to tissue-restricted self-antigens induces airway inflammation and fibrosis following murine lung transplantation

Immune responses against lung-associated self-antigens (self-Ags) are hypothesized to play a role in the development of chronic lung graft rejection. We determined whether immune responses to lung self-Ags, K-alpha-1-tubulin (Kα1T) and Collagen V (Col-V) in the absence of alloimmunity, could promote airway inflammation and fibrosis. Following syngeneic murine orthotopic lung transplantation (LTx) we administered antibodies (Abs) to either Kα1T or Col-V or in combination to both of these self-Ags. As compared to recipients of isotype control Abs, Kα1T Abs and/or Col-V Abs-treated recipients had marked lung graft cellular infiltration and bronchiolar fibrosis. This inflammation was also associated the accumulation of Kα1T and Col-V-specific interferon-γ+ and IL-17+ T cells. Notably, the administration of Abs to Kα1T led to cellular and humoral immune responses to Col-V prior to development of fibrosis, and vice versa, indicating that epitope spreading can occur rapidly in an alloantigen independent manner. Collectively, these data support a model of chronic LTx rejection where the progressive loss of self-tolerance through epitope spreading promotes airway fibrosis. Strategies that target autoreactive Abs may be useful to inhibit chronic rejection of lung grafts.

Effects of preexisting autoimmunity on heart graft prolongation after donor-specific transfusion and anti-CD154

BACKGROUND

Alloreactive memory T cells prevent costimulatory blockade-induced heart graft survival in mice, but whether and how preexisting autoreactive T cells affect solid-organ transplants under these conditions is unknown.

METHODS

We tested the impact of preexisting cardiac myosin (CM)-specific immunity on murine heart transplant recipients treated with donor-specific transfusion (DST) plus anti-CD154 monoclonal antibody MR1.

RESULTS

Preimmunization with CM but not control ovalbumin abrogated the graft prolonging effects of DST/MR1, whether administered 2 weeks or more than 6 weeks before transplantation. Adoptive transfer of spleen cells from CM-immunized mice into naïve recipients had similar effects. CM-specific immunity did not cross-react with donor antigens and preimmunization with CM had no impact on the survival or histology of DST/MR1-treated syngeneic heart grafts, the latter indicating that persistent autoimmunity is insufficient to cause rejection in the context of costimulatory blockade. We observed that the CM preimmunized mice produced higher frequencies of donor-reactive T cells with higher ratios of CD8/CD4Foxp3 cells, suggesting that the autoreactive memory T cells provide help for activation of alloreactive T cells despite the costimulatory blockade.

CONCLUSIONS

These mechanistic insights linking autoimmunity and alloimmunity in a model of murine heart transplantation have clinical relevance to the known association between autoimmunity and an elevated risk of acute and chronic heart transplant injury in humans.

Natural killer cells in rejection and tolerance of solid organ allografts

PURPOSE OF REVIEW

A series of recent studies defy conventional wisdom by showing that natural killer (NK) cells exert a powerful and long-lasting influence on the immune response to whole organ allografts. The early activation of NK cells following transplantation is associated with killing of allogeneic target cells and release of immunomodulatory chemokines and cytokines, which can contribute to either rejection or tolerance. Here, we review findings describing NK cell receptors, potential mediators and mechanisms underlying the dual influence of NK cells in solid organ transplantation.

RECENT FINDINGS

New studies show that NK cells can discriminate between self and foreign tissues and play a key role in the initiation and regulation of adaptive immune responses after solid organ transplantation. Depending upon the types of NK cell receptors engaged and the nature of cytokines released, early NK cell activation can promote either rejection or tolerance.

SUMMARY

Solid organ transplantation is associated with the early activation of NK cells, which are then licensed to kill allogeneic target cells directly or via antibody-dependent cellular cytotoxicity and release various chemokines and immunomodulatory cytokines. Depending upon the nature of NK cell subsets activated and their ability to kill allogeneic target cells and release certain types of cytokines, NK cells can promote the activation/expansion of pro-inflammatory Th1 cells or regulatory Th2/Treg cells thus tilting the balance of alloimmunity towards rejection or tolerance. An in-depth understanding of these mechanisms will be necessary in order to design therapies targeting NK cells in human transplantation.

Role of anti-vimentin antibodies in allograft rejection

Production of anti-vimentin antibodies (AVA) after solid organ transplantation are common. Although classically thought to be expressed mainly within the cytosol, recent evidence demonstrates that extracellular or cell surface expression of vimentin is not unusual. This review examines the evidence to assess whether AVA contribute to allograft pathology. Clinical studies suggest that AVA are associated with cardiac allograft vasculopathy in heart transplant recipients. Studies in non-human primates confirm that production of AVA after renal and heart transplantation are not inhibited by Cyclosporine. Experimental studies have demonstrated that mice pre-immunised with vimentin undergo accelerated acute rejection and vascular intimal occlusion of cardiac allografts. Adoptive transfer of hyperimmune sera containing AVA into B-cell-knock-out mice caused accelerated rejection of allografted hearts, this is clear evidence that antibodies to vimentin accelerate rejection. AVA act in concert with the alloimmune response and AVA do not damage syngeneic or native heart allografts. Confocal microscopy of allografted organs in vimentin immunised mice shows extensive expression of vimentin on endothelial cells, apoptotic leukocytes and platelet/leukocyte conjugates, co-localising with C4d. One explanation for the ability of AVA to accelerate rejection would be fixation of complement within the graft and subsequent pro-inflammatory effects; there may also be interactions with platelets within the vasculature.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

B cells in cardiac transplants: from clinical questions to experimental models

After many years of debate, there is now general agreement that B cells can participate in the immune response to cardiac transplants. Acute antibody-mediated rejection (AMR) is the best defined manifestation of B cell responses, but diagnostic and mechanistic questions still surround AMR. Many complement dependent mechanisms of antibody-mediated injury have been elucidated. C5 has become a therapeutic target that may not just truncate complement activation, but also may tip the balance away from inflammation by altering macrophage function. Additional complement independent effects have been identified. These may escape diagnosis and progress to chronic graft injury. The function of B cell infiltrates in cardiac transplants is even more enigmatic. Nodular endocardial infiltrates that contain B cells and plasma cells have been described in protocol biopsies of cardiac transplants for decades, but an understanding of their significance is still evolving based on more critical morphological and molecular evaluation of these infiltrates. A range of infiltrates containing B cells has also been described in the epicardial fat in transplants with advanced chronic rejection. B cells have been observed in endocardial and epicardial tertiary lymphoid nodules, but their impact on antigen presentation or antibody production remains to be determined. Experimental models in small and large animals suggest that B cells could be essential for the formation of lymphoid nodules through cytokine production. Similarly, the role of proinflammatory adipokines in the formation or function of epicardial lymphoid nodules has not been studied. These clinical observations provide critical questions to be addressed in experimental models.

Autoimmune sensitization to cardiac myosin leads to acute rejection of cardiac allografts in miniature swine

BACKGROUND

Recent studies in mice and patients suggest that posttransplantation induction of autoimmune responses to tissue-specific antigens contributes to the rejection of major histocompatibility complex mismatched allotransplants. The relevance of this phenomenon to the rejection of major and minor histocompatibility-mismatched allografts performed in large-animal models remains to be established.

METHODS

Miniature swine were immunized with cardiac myosin (CM) in Freund's adjuvant and received heterotopic, minor antigen-mismatched heart transplants. T-cell (proliferation and delayed type hypersensitivity [DTH]) and B-cell (antibody) responses specific to CM were measured. The rejection of heart transplants was assessed histologically.

RESULTS

Three of four swine that were immunized with CM before receiving a minor antigen-mismatched heart transplant exhibited potent DTH, T-cell proliferation and antibody responses to CM and rejected their grafts acutely. The fourth swine, which failed to mount a significant DTH response to CM and displayed low and transient anti-CM antibody titers, demonstrated long-term allograft survival.

CONCLUSIONS

This large-animal study supports the relevance of autoimmunity to CM in the rejection of minor antigen disparate cardiac allotransplants.

Anticardiac myosin immunity and chronic allograft vasculopathy in heart transplant recipients

Chronic allograft vasculopathy (CAV) contributes to heart transplant failure, yet its pathogenesis is incompletely understood. Although cellular and humoral alloimmunity are accepted pathogenic mediators, animal models suggest that T cells and Abs reactive to graft-expressed autoantigens, including cardiac myosin (CM), could participate. To test the relationship between CAV and anti-CM autoimmunity in humans, we performed a cross-sectional study of 72 heart transplant recipients: 40 with CAV and 32 without. Sera from 65% of patients with CAV contained anti-CM Abs, whereas <10% contained Abs to other autoantigens (p < 0.05), and only 18% contained anti-HLA Abs (p < 0.05 versus anti-CM). In contrast, 13% of sera from patients without CAV contained anti-CM Abs (p < 0.05; odds ratio [OR], associating CAV with anti-CM Ab = 13, 95% confidence interval [CI] 3.79-44.6). Multivariable analysis confirmed the association to be independent of time posttransplant and the presence of anti-HLA Abs (OR = 28, 95% CI 5.77-133.56). PBMCs from patients with CAV responded more frequently to, and to a broader array of, CM-derived peptides than those without CAV (p = 0.01). Detection of either CM-peptide-reactive T cells or anti-CM Abs was highly and independently indicative of CAV (OR = 45, 95% CI 4.04-500.69). Our data suggest detection of anti-CM immunity could be used as a biomarker for outcome in heart transplantation recipients and support the need for further studies to assess whether anti-CM immunity is a pathogenic mediator of CAV.

Antibodies reactive to non-HLA antigens in transplant glomerulopathy

Although T and B cell alloimmunity contribute to transplant injury, autoimmunity directed at kidney-expressed, non-HLA antigens may also participate. Because the specificity, prevalence, and importance of antibodies to non-HLA antigens in late allograft injury are poorly characterized, we used a protein microarray to compare antibody repertoires in pre- and post-transplant sera from several cohorts of patients with and without transplant glomerulopathy. Transplantation routinely induced changes in antibody repertoires, but we did not identify any de novo non-HLA antibodies common to patients with transplant glomerulopathy. The screening studies identified three reactivities present before transplantation that persisted after transplant and strongly associated with transplant glomerulopathy. ELISA confirmed that reactivity against peroxisomal-trans-2-enoyl-coA-reductase strongly associated with the development of transplant glomerulopathy in independent validation sets. In addition to providing insight into effects of transplantation on non-HLA antibody repertoires, these results suggest that pretransplant serum antibodies to peroxisomal-trans-2-enoyl-coA-reductase may predict prognosis in kidney transplantation.

Autoimmunity to vimentin potentiates graft vasculopathy in murine cardiac allografts

BACKGROUND

There is increasing evidence for a role for autoimmunity in transplant rejection. It has previously been shown that autoantibodies to vimentin (Vim) accelerate acute rejection of murine cardiac allografts. We have investigated whether autoimmunity to Vim contributes to development of cardiac allograft vasculopathy (CAV).

METHODS

Two well-established minor mismatch murine models of CAV were used, transplantation of 129/sv hearts into T-cell-depleted C57Bl/6 (B6) recipients and transplantation of FVB hearts into nonimmunosuppressed DBA/1 recipients. Recipients were immunized with recombinant mouse Vim in complete Freunds adjuvant, and controls received hen egg lysozyme 2 weeks before transplantation. T cell and antibody responses to Vim were assessed by ELISPOT and ELISA, respectively. CAV within transplanted hearts was assessed by quantitative morphometry of occluded vessels, presence of smooth muscle cells, deposition of C3d, and confocal microscopy.

RESULTS

Allografts were harvested from B6 recipients at days 30 and 45 and from DBA/1 recipients at days 18 and 35. At all days, there was significantly more intimal occlusion of arteries of Vim -immunized mice than controls. There was significantly more smooth muscle cell alpha actin in vessels from Vim-immunized mice, and more C3d deposited in hearts from Vim-immunized mice. Confocal microscopy demonstrated colocalization of Vim with C3d on endothelial cells, leukocytes, and platelets in allogeneic but not syngeneic hearts. Serum from Vim-immunized mice, but not controls, caused platelet/leukocyte conjugation when added to mouse leukocytes.

CONCLUSION

The autoimmune response to Vim accelerates CAV progression in these minor-mismatched models.

Humoral autoimmunity and transplant vasculopathy: when allo is not enough

For several decades, allograft rejection was believed to be mediated almost exclusively by cellular immune responses, but it is now realized that humoral responses also play a major role. Although directed typically against donor human leukocyte antigen, it is becoming increasingly evident that the antibody response can also target autoantigens that are shared between donor and recipient and that this autoantibody may contribute to graft rejection. Many aspects of transplant-induced humoral autoimmunity remain poorly understood and key questions persist; not least what triggers the response and how autoantibody causes graft damage. Here, we collate results from recent clinical and experimental studies in transplantation and autoimmune diseases to propose answers to these questions.

Characterization of immune responses to cardiac self-antigens myosin and vimentin in human cardiac allograft recipients with antibody-mediated rejection and cardiac allograft vasculopathy

BACKGROUND

Herein we study the role of donor-specific antibodies (DSA) to mismatched human leukocyte antigen (HLA) and antibodies (Abs) to the cardiac self-antigens myosin (MYO) and vimentin (VIM) in the pathogenesis of acute antibody-mediated rejection (AMR) in the early post-transplant period (EP, <12 months) and cardiac allograft vasculopathy (CAV) in the late post-transplant period (LP, >12 months) after heart transplantation (HTx).

METHODS

One hundred forty-eight HTx recipients (65 in EP, 83 in LP) were enrolled in the study. Development of DSA was determined by Luminex. Circulating Abs against MYO and VIM in sera were measured using enzyme-linked immunoassay (ELISA). Frequency of CD4+ T-helper cells (CD4+ Th) secreting interferon (IFN)-γ, interleukin (IL)-17, IL-10 or IL-5 specific to either MYO or VIM were analyzed in vitro using ELISpot assays.

RESULTS

AMR patients were more likely DSA positive (AMR-: 15%; AMR+: 70%; p = 0.03) and demonstrated increased Abs to MYO (AMR-: 144 ± 115 μg/ml; AMR+: 285 ± 70 μg/ml; p = 0.033) and VIM (AMR-: 37 ± 19 μg/ml; AMR+: 103 ± 43 μg/ml; p = 0.014). AMR patients demonstrated increased IL-5 CD4+ Th cells specific to MYO (5.2 ± 0.9 fold, p = 0.003) and VIM (7.3 ± 2.9-fold, p = 0.004) and decreased IL-10 CD4+ Th cells specific to MYO (2.2 ± 0.4-fold, p = 0.009) and VIM (1.7 ± 0.2-fold, p = 0.03). CAV patients were more likely DSA positive (CAV-): 25%; CAV+: 79%; p = 0.03) and demonstrated increased Abs to MYO (CAV-: 191 ± 120 μg/ml; CAV+: 550 ± 98 μg/ml; p = 0.025) and VIM (CAV-: 55 ± 25 μg/ml; CAV+: 255 ± 49 μg/ml; p = 0.001). CAV patients demonstrated increased IL-17 CD4+ Th cells specific to MYO (10.5 ± 7.3-fold, p = 0.002) and VIM (7.0 ± 3.9-fold, p = 0.003).

CONCLUSIONS

The presence of DSA in AMR and CAV is significantly associated with development of Abs to MYO and VIM in post-HTx patients. Induction of high CD4+ Th cells specific to cardiac self-antigens that secrete predominantly IL-5 and IL-17 plays a significant role in the development of Abs to self-antigens leading to AMR and CAV, respectively.

Dual effects of the alloresponse by Th1 and Th2 cells on acute and chronic rejection of allotransplants

The contribution of direct and indirect alloresponses by CD4(+) Th1 and Th2 cells in acute and chronic rejection of allogeneic transplants remains unclear. In the present study, we addressed this question using a transplant model in a single MHC class I-disparate donor-recipient mouse combination. BALB/c-dm2 (dm2) mutant mice do not express MHC class I L(d) molecules and reject acutely L(d+) skin grafts from BALB/c mice. In contrast, BALB/c hearts placed in dm2 mice are permanently accepted in the absence of chronic allograft vasculopathy. In this model, CD4(+) T cells are activated following recognition of a donor MHC class I determinant, L(d) 61-80, presented by MHC Class II A(d) molecules on donor and recipient APC. Pre-transplantation of recipients with L(d) 61-80 peptide emulsified in complete Freund's adjuvant induced a Th1 response, which accelerated the rejection of skin allografts, but it had no effect on cardiac transplants. In contrast, induction of a Th2 response to the same peptide abrogated the CD8(+) cytotoxic T cells response and markedly delayed the rejection of skin allografts while it induced de novo chronic rejection of heart transplants. This shows that Th2 cells activated via indirect allorecognition can exert dual effects on acute and chronic rejection of allogeneic transplants.

Autoimmune responses against renal tissue proteins in long-term surviving allograft recipients

Major histocompatibility complex antigens (MHC) are classical targets of recipient responses to allotransplants. However, the role of an immune response directed against autologous graft tissue determinants is poorly defined. In this study, we investigated (i) whether autologous kidney tissue extract can induce an immune response to autologous kidney proteins in normal rats, and (ii) if a similar autologous response develops in the long-term surviving LEW.1A recipients of an MHC-mismatched LEW.1W kidney (RT1(u) to RT1(a)). LEW.1A rats immunized with allo- or syngeneic soluble kidney extracts developed a T-cell response to self antigens as shown by the frequency of specific IFN-gamma-producing T cells from LEW.1A rats in the presence of extracts (ELISPOT). In contrast, they responded only marginally to dominant RT1(u) determinants. The ELISPOT against fractions of soluble autologous kidney extracts separated by an FPLC gel-filtration system indicated a preferential response to megalin, a high molecular weight protein that has been shown to be involved in experimental Heymann nephritis. In a model of long-term kidney allograft survival by anti-CD28 administration, recipients also developed humoral but not cellular responses to megalin. Our data suggest that autoimmune processes develop in long-term surviving kidney allograft recipients.

Donor CD4 T cells contribute to cardiac allograft vasculopathy by providing help for autoantibody production

BACKGROUND

The development of autoantibody after heart transplantation is increasingly associated with poor graft outcome, but what triggers its development and whether it has a direct causative role in graft rejection is not clear. Here, we study the development of antinuclear autoantibody in an established mouse model of heart allograft vasculopathy.

METHODS AND RESULTS

Humoral vascular changes, including endothelial complement staining, were present in bm12 heart grafts, explanted 50 days after transplantation. Alloantibody was not detectable, but long-lasting autoantibody responses developed in C57BL/6 recipients from the third week after transplantation. No autoantibody was generated if donor CD4 T cells were depleted before heart graft retrieval or in recipients that lacked B-cell major histocompatibility complex class II expression, indicating that humoral autoimmunity is a consequence of donor CD4 T-cell allorecognition of the major histocompatibility complex class II complex on recipient autoreactive B cells. An effector role for autoantibody in graft rejection was confirmed by abrogation of humoral vascular rejection, and attenuation of vasculopathy, in B-cell deficient recipients and by development of vascular obliteration and accelerated rejection in recipients primed for autoantibody before transplantation.

CONCLUSIONS

Passenger CD4 T cells within heart transplants can contribute to allograft vasculopathy by providing help to recipient B cells for autoantibody generation.

The indirect alloresponse impairs the induction but not maintenance of tolerance to MHC class I-disparate allografts

We studied the effects of indirect allorecognition on the induction and maintenance phases of tolerance in miniature swine cotransplanted with heart and kidney allografts. MHC class I-mismatched heart and kidney grafts were cotransplanted in recipients receiving CyA for 12 days. Recipients were unimmunized or immunized with a set of donor-derived or control third-party MHC class I peptides either 21 days prior to transplantation or over 100 days after transplantation. T-cell proliferation, delayed type hypersensitivity reaction (DTH) and antibody production were assessed. All animals injected with donor MHC class I peptides developed potent indirect alloresponses specific to the immunizing peptides. While untreated recipients developed stable tolerance, all animals preimmunized with donor allopeptides rejected kidney-heart transplants acutely. In contrast, when peptide immunization was delayed until over 100 days after kidney-heart transplantation, no effects were observed on graft function or in vitro measures of alloimmunity. Donor peptide immunization prevented tolerance when administered to recipients pre transplantation but did not abrogate tolerance when administered to long-term survivors post transplantation. This suggests that the presence of T cells activated via indirect allorecognition represent a barrier to the induction but not the maintenance of tolerance.

De novo autoimmunity after organ transplantation: targets and possible pathways

The development of autoantibodies to different tissue-specific antigens in patients without existing history of autoimmune diseases suggests that autoimmunity may develop de novo after organ transplantation. In addition to allo-specific immune responses, tissue-specific autoimmunity also appears contribute to the host anti-graft response, and thus may affect long-term graft function. As graft failure caused by chronic rejection is a major challenge in clinical transplantation, understanding de novo autoreactivity after transplantation has important ramifications. This review investigates this emerging concept by discussing target antigens and possible pathways.

Treatment with encapsulated Hsp60 peptide (p277) prolongs skin graft survival in a murine model of minor antigen disparity

The increased expression of heat shock protein (Hsp)60 in different kinds of graft tissues has been associated with a proinflammatory role and rejection. However, there are very few reports in which treatment with Hsp60 delays skin allograft rejection. The aim of this work was to evaluate the capacity of encapsulated human Hsp60-derived peptide p277 to delay graft rejection in two murine models of skin transplantation with minor antigen disparities. Briefly, BALB/c mice and C57BL/6 were intranasally pre-treated with five doses of Hsp60 p277 peptide encapsulated in polylactide-co-glycolide acid microspheres (PLGM), and received skin grafts from DBA2 mice and 129/B6 (F1) mice respectively. The treatment with the peptide increased skin graft survival more than 20 days in both the mouse strains, mainly in C57BL/6 recipients (P < 0.05). Also, p277-treated BALB/c and C57BL/6 mice showed IL-10 and IFN-gamma production, induced by p277 peptide. For the first time, a mucosal schedule using the Hsp60 C-terminal peptide p277 encapsulated in PLGM showed some survival prolongation of skin grafts bearing minor antigen disparities. Our results suggest a potential role for Hsp60-based therapy and the mucosal route as a useful tool to control the inflammatory response to allografts.

Autoantibodies to vimentin cause accelerated rejection of cardiac allografts

Autoimmune responses to vimentin occur after solid organ transplantation, but their pathogenic effects are unclear. The aim of these studies was to investigate the effects of vimentin preimmunization on allogeneic and isografted hearts in a murine transplant model. Immunization of C57BL/6 mice with murine vimentin in complete Freund's adjuvant resulted in anti-vimentin antibodies and vimentin-reactive Th-1 cells. Transplantation of 129/sv hearts into vimentin-immunized C57BL/6 recipients resulted in accelerated rejection (8.4 +/- 1.5 days; n = 18), compared with hen egg lysozyme-immunized C57BL/6 (13.3 +/- 2.2 days; n = 10; P < 0.0001, log-rank test). In contrast, isografts continued to beat beyond 90 days. Immunohistochemical analysis of allografts from vimentin/complete Freund's adjuvant mice demonstrated increased numbers of T cells and enhanced microvascular deposition of C3d, CD41, and P-selectin compared with controls. Antibodies were necessary for accelerated rejection, shown by the fact that vimentin-immunized B-cell-deficient IgH6 mice did not show accelerated rejection of 129/sv allografts, but rejection was restored by adoptive transfer of serum containing anti-vimentin antibodies. Eluates from donor hearts placed in vimentin/complete Freund's adjuvant recipients contained anti-vimentin antibodies, shown by Western blotting. Confocal imaging of rejected hearts de-monstrated presence of vimentin and C3d on apoptosed leukocytes, endothelial cells, and platelet/leukocyte conjugates. These results demonstrate that autoantibodies to vimentin, in conjunction with the alloimmune response, have a pathogenic role in allograft rejection.

Tolerance in Heart Transplantation: The Holy Grail, or an Attainable Goal?

The father of cardiac transplantation, Norman Shumway, famously predicted that tolerance was the future of the field, and always would be. Although his prediction remains true to date, significant progress has been made toward this goal, the "Holy Grail" for transplant clinicians. Current efforts are fueled by disappointing long-term outcomes associated with chronic immunosuppression, and the promise that partial or complete tolerance will impact long-term results favorably. This article provides a clinical definition of tolerance primarily based on lessons learned from animal heart allograft models. It reviews several promising strategies for inducing tolerance and detecting its presence through the use of biomarkers in peripheral blood or the graft, and outlines a possible path toward making this vision a clinical reality.

Cellular autoreactivity against heat shock protein 60 in renal transplant patients: peripheral and graft-infiltrating responses

Autoreactivity to heat shock protein 60 (Hsp60) has been implicated in the pathogenesis and regulation of chronic inflammation, especially in autoimmune diseases. In transplantation, there is a lack of information regarding the cytokine profile and specificity of cells that recognize self-Hsp60 as well as the kinetics of autoreactivity following transplantation. We studied the cellular reactivity of peripheral and graft-infiltrating lymphocytes against Hsp60 in renal transplant patients. Cytokine production induced by this protein in peripheral blood mononuclear cells indicated a predominance of interleukin (IL)-10 during the late post-transplantation period, mainly in response to intermediate and C-terminal peptides. Patients with chronic rejection presented reactivity to Hsp60 with a higher IL-10/interferon (IFN)-gamma ratio compared to long-term clinically stable patients. Graft-infiltrating T cell lines, cocultured with antigen-presenting cells, preferentially produced IL-10 after Hsp60 stimulation. These results suggest that, besides its proinflammatory activity, autoreactivity to Hsp60 in transplantation may also have a regulatory role.

B Cell-Mediated Antigen Presentation Is Required for the Pathogenesis of Acute Cardiac Allograft Rejection

Acute allograft rejection requires the activation of alloreactive CD4 T cells. Despite the capacity of B cells to act as potent APCs capable of activating CD4 T cells in vivo, their role in the progression of acute allograft rejection was unclear. To determine the contribution of B cell APC function in alloimmunity, we engineered mice with a targeted deficiency of MHC class II-mediated Ag presentation confined to the B cell compartment. Cardiac allograft survival was markedly prolonged in these mice as compared to control counterparts (median survival time, >70 vs 9.5 days). Mechanistically, deficient B cell-mediated Ag presentation disrupted both alloantibody production and the progression of CD4 T cell activation following heart transplantation. These findings demonstrate that indirect alloantigen presentation by recipients' B cells plays an important role in the efficient progression of acute vascularized allograft rejection.

Comparison of host response to polypropylene and non-cross-linked porcine small intestine serosal-derived collagen implants in a rat model

OBJECTIVE

To compare the host response, architectural integration and tensile strength of polypropylene and porcine small intestine submucosa-derived implants in a rat model.

DESIGN

Experimental study.

SETTING

Center for Surgical Technologies, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium.

SAMPLE

Forty-eight adult male Wistar rats weighing 220-250 g randomised to receive either implant.

METHODS

Full thickness abdominal wall defects were primarily repaired with polypropylene mesh (Marlex) (MX group) or porcine small intestine submucosa (Surgisis) (SIS group). Animals were sacrificed at 7, 14, 30 and 90 days after implantation.

MAIN OUTCOME MEASURES

The presence of herniation, infection and intra-peritoneal adhesions. Change in thickness and tensile strength of implant. Histopathological and immunohistochemical appearances of inflammatory response and collagen deposition.

RESULTS

Implants from the SIS group showed a short term increase in thickness in the first 14 days. Formation of adhesions was significantly more intense in the MX group at 30 days, and more extensive in the SIS group at 90 days. Tensile strength increased over time in both groups but was significantly lower in the SIS group than the MX group at 30 days. Implants in the MX group showed a more pronounced inflammatory response and more pronounced new vessel formation than the SIS group. Collagen formation was initially more fibrous and better organised in the MX group but became greater in the SIS group at 90 days.

CONCLUSIONS

Biologically derived implant material induced a less pronounced inflammatory response and differences in collagen deposition. At 30 days tensile strength was weaker in the biological implant group but was equivalent by 90 days. These differences may have implications for the in vivo performance of the materials.

Phenotypically and Functionally Distinct CD8+ Lymphocyte Populations in Long-Term Drug-Free Tolerance and Chronic Rejection in Human Kidney Graft Recipients

A substantial proportion of long-term kidney graft recipients, including those with a stable renal function in the absence of immunosuppressive therapy, present a skewed T cell receptor (TCR) Vbeta chain usage, essentially in the CD8+ subset. This study analyzed in more detail phenotypical and functional alterations of CD8+ lymphocytes in drug-free tolerant patients (DF-Tol) compared with recipients with chronic rejection (CR). Phenotyping revealed a significant increase in central memory and a decrease in effector CD8+ lymphocytes in DF-Tol versus CR. The expression of CD28+ and CD27+ on these effector cells was significantly decreased in CR. These profiles were stable over time and independent of treatment. Functionally, the CD8+CD28- lymphocytes were less sensitive to apoptosis than their CD8+CD28+ counterparts, without differences in polyclonal proliferation. The CD8+CD28- cells did not express GITR and FoxP3 but were characterized by high levels of preformed perforin and granzyme A, pointing toward a cytotoxic rather than a suppressor function. CD8+CD28- lymphocytes did not show antigen-specific degranulation when co-cultured with targets that bear donor HLA class I antigens, suggesting that the cytotoxicity is directed either to other determinants of the graft or to nongraft epitopes. Of interest, CD8+ cells from DF-Tol displayed the same profile as healthy individuals, indicating an increase in CD8+CD28- effector lymphocytes in CR rather than a decrease in DF-Tol. CD8+ lymphocytes from stable kidney recipients under conventional maintenance immunosuppression displayed a mixed profile, independent of treatment and time of sampling. Taken collectively, these data show a strong cytotoxicity-associated CD8+CD28- signature in CR and suggest a suppression of pathologic cytotoxicity in DF-Tol. Further prospective studies should assess whether serial CD8+ phenotyping may help to identify patients who are at risk for CR when immunosuppression is tapered.

Tissue migration by parasitic helminths – an immunoevasive strategy?

Migration through host tissues has major costs for parasitic helminths in terms of energy expenditure, risks of attrition and the need to adapt to varying physicochemical environments. Nevertheless, such migratory phases seem to confer a specific survival advantage. One reason for this might be the avoidance of specific host immune-defence mechanisms designed to protect against threats at mucosal surfaces.

Progression of alloresponse and tissue-specific immunity during graft coronary artery disease

Chronic rejection remains the major obstacle for long-term transplant survival. Both indirect alloresponse and tissue-specific autoimmunity have been implicated in its pathogenesis. The interrelationship between these two types of host anti-graft response remains poorly understood. We have developed an immunosuppression-free mouse model of graft coronary artery disease (GCAD), in which all FVB (H-2(q)) cardiac allografts placed into minor Ag (mHC)-mismatched DBA/1 (H-2(q)) hosts survived more than 112 days, and developed GCAD. We then examined the kinetics of both anti-mHC alloresponse and host autoimmunity against heart-specific antigen, cardiac myosin (CM). At 8 days post-transplantation, recipient mice showed minimal intragraft inflammation and apoptosis, and limited expansion of allo-specific T cells. In addition, we observed early production of anti-myosin IgG1 autoantibodies, which occurred in the absence of activated CM-specific T lymphocytes. By day 56, GCAD indices, the numbers of mHC- and CM-reactive T cells, and the levels of circulating allo- and CM-specific antibodies were all significantly increased. While host alloresponse was exhausted at 112 days post-transplant, T-cell reactivity against CM persisted. Our data suggest that both allo- and tissue-specific immunity might contribute to the induction of GCAD. They indicate that continual autoimmune response against graft tissue antigens may provide for GCAD sustenance.

Donor-Specific Antibodies in Allograft Rejection: Clinical and Experimental Data

The ability of donor-specific major histocompatibility complex alloantibodies to destroy a transplanted organ within minutes, the so-called hyperacute rejection phenomenon, has been known for a long time. It is a clear demonstration of the possible cytotoxic effect of antibodies. Apart from this particular situation, the role of antibodies in inducing acute or chronic allograft rejection remains controversial. Many clinical data have shown that transplant recipients capable of developing class I or class II anti-HLA antibodies experienced shorter survival periods than those who were not. This fact, in accordance with experimental data, only demonstrates that high antibody responders reject a transplant more easily than low responders. More interestingly, there is now increasing evidence that posttransplant appearance of donor-specific alloantibodies, and probably of alloreactive-induced autoantibodies, is strongly correlated with reduced graft survival rate, especially from chronic rejection. We demonstrated that donor-specific HLA antibodies can be found in more than 70% of transplanted kidneys with chronic allograft nephropathy, and that the intragraft presence of such antibodies is significantly correlated with high numbers of plasma cells on early biopsies and C4d deposits, a recognized marker of humoral rejection. It is likely that non-HLA antibodies also play a deleterious role in organ transplant outcome, particularly the heterogeneous group of anti-endothelial cells antibodies, anti-MIC antibodies, autoantibodies and some others with no recognized target. Convincing experimental data, especially using B cell and T cell deficient mice, strongly suggest that B cells and donor-specific antibodies are required for fully developed chronic allograft rejection. The role of antibodies in inducing the cascade of cytokines and growth factors leading to tissue lesions is of increasing interest since it is now possible to control B cell proliferation and antibody production.

Host response after reconstruction of abdominal wall defects with porcine dermal collagen in a rat model

OBJECTIVE

The purpose of this study was to compare the inflammatory response after implantation of Pelvicol with Prolene in a rat model.

STUDY DESIGN

Full-thickness abdominal wall defects were created in 64 Wistar rats, and reconstructed with either Pelvicol or Prolene. Animals were sacrificed on days 7, 14, 30, and 90 to evaluate the presence of herniation, infection, adhesions, and changes in thickness and tensile strength of the implants. Histopathology and immunohistochemistry were performed to evaluate the collagen deposition and the inflammatory response. Statistics were done with unpaired t test and Mann-Whitney rank test.

RESULTS

Pelvicol implantation induced infiltration of granulocytes, macrophages, and NK cells, which showed up-regulated expression of surface activation markers ICAM-1 and CD11b. This inflammatory response was significantly milder, and declined faster than in Prolene-implanted rats, and was also associated with fewer adhesions. Moreover, Pelvicol induced a slower, but more orderly collagen deposition, paralleling the surface of the implant. Pelvicol implants showed a slower increase in thickness and tensile strength early on, but this difference disappeared by day 90.

CONCLUSION

Pelvicol induces a milder inflammatory response, less adhesion formation, more orderly collagen deposition than Prolene, and reaches a comparable tensile strength only after 90 days.

Role of autoimmunity in organ allograft rejection: a focus on immunity to type V collagen in the pathogenesis of lung transplant rejection

Lung transplantation is the only definitive treatment modality for many forms of end-stage lung disease. However, the lung is rejected more often than any other type of solid organ allograft due to chronic rejection known as bronchiolitis obliterans (BO). Indeed, BO is the primary reason why the 5- and 7-yr survival rates are worse for the lung than for any other transplanted organ. Alloimmunity to donor antigens is established as the primary mechanism that mediates rejection responses. However, newer immunosuppressive regimens designed to abrogate alloimmune activation have not improved survival. Therefore, these data suggest that other antigens, unrelated to donor transplantation antigens, are involved in rejection. Utilizing human and rodent studies of lung transplantation, our laboratory has documented that a native collagen, type V collagen [col(V)], is a target of the rejection response. Col(V) is highly conserved; therefore, these data indicate that transplant rejection involves both alloimmune and autoimmune responses. The role of col(V) in lung transplant rejection is described in this review article. In addition, the potential role of regulatory T cells that are crucial to modulating autoimmunity and alloimmunity is also discussed.

What's new and what's hot in transplantation: basic science ATC 2003

It has been approximately 50 years since the initial descriptions of acquired transplant tolerance, and our understanding of the immune response to a transplanted organ has progressed enormously during the ensuing years. Recent studies have shed new light on the molecular and cellular basis of transplant rejection, have better defined the mechanisms of allograft tolerance with particular emphasis on a role for regulatory T cells, have identified important new hurdles to overcome in order to prolong allograft survival, have brought xenotransplantation closer to becoming a clinical reality, and have led to the development of novel techniques that may permit analysis of immune responses to transplanted organs in vivo.

T-cell allorecognition and transplant rejection: a summary and update

Transplant biologists have made significant progress over the last 20 years towards unraveling the immunologic intricacies of allograft rejection. This large body of work has resulted in an improved understanding of T-cell allorecognition at a molecular level and has provided new insight into the functional consequences resulting from the allorecognition events. The findings suggest that the survival and the histologic features of a transplanted organ are influenced not only by the T-cell recognition pathway, but also by the frequency, the induced effector functions and the specific cellular targets of the alloreactive T-cell repertoire.