Immune Responses to Tissue-Restricted Nonmajor Histocompatibility Complex Antigens in Allograft Rejection

Generating an organ-deficient animal model using a multi-targeted CRISPR-Cas9 system

Gene-knockout animal models with organ-deficient phenotypes used for blastocyst complementation are generally not viable. Animals need to be maintained as heterozygous mutants, and homozygous mutant embryos yield only one-fourth of all embryos. In this study, we generated organ-deficient embryos using the CRISPR-Cas9-sgRNAms system that induces cell death with a single-guide RNA (sgRNAms) targeting multiple sites in the genome. The Cas9-sgRNAms system interrupted cell proliferation and induced cell ablation in vitro. The mouse model had Cas9 driven by the Foxn1 promoter with a ubiquitous expression cassette of sgRNAms at the Rosa26 locus (Foxn1Cas9; Rosa26_ms). It showed an athymic phenotype similar to that of nude mice but was not hairless. Eventually, a rat cell-derived thymus in an interspecies chimera was generated by blastocyst complementation of Foxn1Cas9; Rosa26_ms mouse embryos with rat embryonic stem cells. Theoretically, a half of the total embryos has the Cas9-sgRNAms system because Rosa26_ms could be maintained as homozygous.

Role of the immune system in liver transplantation and its implications for therapeutic interventions

Liver transplantation (LT) stands as the gold standard for treating end-stage liver disease and hepatocellular carcinoma, yet postoperative complications continue to impact survival rates. The liver's unique immune system, governed by a microenvironment of diverse immune cells, is disrupted during processes like ischemia-reperfusion injury posttransplantation, leading to immune imbalance, inflammation, and subsequent complications. In the posttransplantation period, immune cells within the liver collaboratively foster a tolerant environment, crucial for immune tolerance and liver regeneration. While clinical trials exploring cell therapy for LT complications exist, a comprehensive summary is lacking. This review provides an insight into the intricacies of the liver's immune microenvironment, with a specific focus on macrophages and T cells as primary immune players. Delving into the immunological dynamics at different stages of LT, we explore the disruptions after LT and subsequent immune responses. Focusing on immune cell targeting for treating liver transplant complications, we provide a comprehensive summary of ongoing clinical trials in this domain, especially cell therapies. Furthermore, we offer innovative treatment strategies that leverage the opportunities and prospects identified in the therapeutic landscape. This review seeks to advance our understanding of LT immunology and steer the development of precise therapies for postoperative complications.

The role of lung-restricted autoantibodies in the development of primary and chronic graft dysfunction

Lung transplantation is a life-saving treatment for both chronic end-stage lung diseases and acute respiratory distress syndrome, including those caused by infectious agents like COVID-19. Despite its increasing utilization, outcomes post-lung transplantation are worse than other solid organ transplants. Primary graft dysfunction (PGD)-a condition affecting more than half of the recipients post-transplantation-is the chief risk factor for post-operative mortality, transplant-associated multi-organ dysfunction, and long-term graft loss due to chronic rejection. While donor-specific antibodies targeting allogenic human leukocyte antigens have been linked to transplant rejection, the role of recipient's pre-existing immunoglobulin G autoantibodies against lung-restricted self-antigens (LRA), like collagen type V and k-alpha1 tubulin, is less understood in the context of lung transplantation. Recent studies have found an increased risk of PGD development in lung transplant recipients with LRA. This review will synthesize past and ongoing research-utilizing both mouse models and human subjects-aimed at unraveling the mechanisms by which LRA heightens the risk of PGD. Furthermore, it will explore prospective approaches designed to mitigate the impact of LRA on lung transplant patients.

Extracellular Vesicles Mediate Immune Responses to Tissue-Associated Self-Antigens: Role in Solid Organ Transplantations

Transplantation is a treatment option for patients diagnosed with end-stage organ diseases; however, long-term graft survival is affected by rejection of the transplanted organ by immune and nonimmune responses. Several studies have demonstrated that both acute and chronic rejection can occur after transplantation of kidney, heart, and lungs. A strong correlation has been reported between de novo synthesis of donor-specific antibodies (HLA-DSAs) and development of both acute and chronic rejection; however, some transplant recipients with chronic rejection do not have detectable HLA-DSAs. Studies of sera from such patients demonstrate that immune responses to tissue-associated antigens (TaAgs) may also play an important role in the development of chronic rejection, either alone or in combination with HLA-DSAs. The synergistic effect between HLA-DSAs and antibodies to TaAgs is being established, but the underlying mechanism is yet to be defined. We hypothesize that HLA-DSAs damage the transplanted donor organ resulting in stress and leading to the release of extracellular vesicles, which contribute to chronic rejection. These vesicles express both donor human leukocyte antigen (HLA) and non-HLA TaAgs, which can activate antigen-presenting cells and lead to immune responses and development of antibodies to both donor HLA and non-HLA tissue-associated Ags. Extracellular vesicles (EVs) are released by cells under many circumstances due to both physiological and pathological conditions. Primarily employing clinical specimens obtained from human lung transplant recipients undergoing acute or chronic rejection, our group has demonstrated that circulating extracellular vesicles display both mismatched donor HLA molecules and lung-associated Ags (collagen-V and K-alpha 1 tubulin). This review focuses on recent studies demonstrating an important role of antibodies to tissue-associated Ags in the rejection of transplanted organs, particularly chronic rejection. We will also discuss the important role of extracellular vesicles released from transplanted organs in cross-talk between alloimmunity and autoimmunity to tissue-associated Ags after solid organ transplantation.

Chronic Lung Allograft Dysfunction: Evolving Concepts and Therapies

The primary factor that limits long-term survival after lung transplantation is chronic lung allograft dysfunction (CLAD). CLAD also impairs quality of life and increases the costs of medical care. Our understanding of CLAD continues to evolve. Consensus definitions of CLAD and the major CLAD phenotypes were recently updated and clarified, but it remains to be seen whether the current definitions will lead to advances in management or impact care. Understanding the potential differences in pathogenesis for each CLAD phenotype may lead to novel therapeutic strategies, including precision medicine. Recognition of CLAD risk factors may lead to earlier interventions to mitigate risk, or to avoid risk factors all together, to prevent the development of CLAD. Unfortunately, currently available therapies for CLAD are usually not effective. However, novel therapeutics aimed at both prevention and treatment are currently under investigation. We provide an overview of the updates to CLAD-related terminology, clinical phenotypes and their diagnosis, natural history, pathogenesis, and potential strategies to treat and prevent CLAD.

Dose- and Time-Dependent Effects of Human Mesenchymal Stromal Cell Infusion on Cardiac Allograft Rejection in Mice

Heart transplantation is the final life-saving therapeutic strategy for many end-stage heart diseases. Long-term immunosuppressive regimens are needed to prevent allograft rejection. Mesenchymal stromal cells (MSCs) have been shown as immunomodulatory therapy for organ transplantation. However, the effect of dose and timing of MSC treatment on heart transplantation has not yet been examined. In this study, we infused three doses (1 × 106, 2 × 106, or 5 × 106 cells) of human MSCs (hMSCs) to the recipient BALB/c mice before (7 days or 24 h) or after (24 h) receiving C57BL/6 cardiac transplants. We found that infusion of high dose hMSCs (5 × 106) at 24 h post-transplantation significantly prolonged the survival time of cardiac grafts. To delineate the underlying mechanism, grafts, spleens, and draining lymph nodes were harvested for analysis. Dose-dependent effect of hMSC treatment was shown in: (1) alleviation of International Society of Heart and Lung Transplantation (ISHLT) score in grafts; (2) reduction of the population of CD4+ and CD8+ T cells; (3) increase of regulatory T (Treg) cells; (4) and decrease of serum levels of inflammatory cytokines and donor-specific antibodies. Taken together, we showed timing critical and dose-dependent immunomodulatory effects of hMSC treatment against acute allograft rejection in a mouse model of heart transplantation.

Pre-existing self-reactive IgA antibodies associated with primary graft dysfunction after lung transplantation

BACKGROUND

Primary graft Dysfunction (PGD) results in significant mortality and morbidity after lung transplantation (LT). The objective of this study was to evaluate if pre-existing antibodies to self-antigens in sera of LT recipients are associated with PGD.

METHODS

The serum profiles of IgG and IgA autoantibodies were analyzed using a customized proteomic microarray bearing 124 autoantigens. Autoantibodies were analyzed using Mann-Whitney U test or Fisher exact test. The association of the autoantibodies with clinical phenotypes and survival was analyzed by Kaplan-Meier Survival Analysis. Receiver operating curve characteristics (ROC) were calculated to evaluate the predictive value of the autoantibodies for PGD.

RESULTS

51 patients were included in this study. Autoantigen microarray analysis on the pre-transplantation samples identified 17 IgA and 3 IgG autoantibodies which were significantly higher in recipients who developed PGD compared to those who did not (adjusted p < .05 and fold change>1.5). 6 IgA Abs were significantly associated with survival. Taken as a panel, an elevation of 6 IgA Abs had significant predictive value for PGD. Area under the curve value for the panel was 0.9413 for PGD with ROC analysis. Notably, 6 of the 17 IgA autoantigen targets are belong to proteoglycan family of extracellular matrix proteins.

CONCLUSION

Pre-existing IgG and IgA autoantibodies in LT patients correlate with PGD and with survival in a single center, small cohort of lung transplant recipients. Further validation is needed to confirm the findings in the study.

Immune responses towards bioengineered tissues and strategies to control them

PURPOSE OF REVIEW

Research into development of artificial tissues and bioengineered organs to replace physiological functions of injured counterparts has highlighted a previously underestimated challenge for its clinical translatability: the immune response against biomaterials. Herein, we will provide an update and review current knowledge regarding this important barrier to regenerative medicine.

RECENT FINDINGS

Although a clear understanding of the immune reactivity against biomaterials remains elusive, accumulating evidence indicates that innate immune cells, primarily neutrophils and macrophages, play a key role in the initial phases of the immune response. More recently, data have shown that in later phases, T and B cells are also involved. The use of physicochemical modifications of biomaterials and cell-based strategies to modulate the host inflammatory response is being actively investigated for effective biomaterial integration.

SUMMARY

The immune response towards biomaterials and bioengineered organs plays a crucial role in determining their utility as transplantable grafts. Expanding our understanding of these responses is necessary for developing protolerogenic strategies and delivering on the ultimate promise of regenerative medicine.

Clinical relevance of lung-restricted antibodies in lung transplantation

Lung transplant is a definitive treatment for several end-stage lung diseases. However, the high incidence of allograft rejection limits the overall survival following lung transplantation. Traditionally, alloimmunity directed against human leukocyte antigens (HLA) has been implicated in transplant rejection. Recently, the clinical impact of non-HLA lung-restricted antibodies (LRA) has been recognized and extensive research has demonstrated that they may play a dominant role in the development of lung allograft rejection. The immunogenic lung-restricted antigens that have been identified include amongst others, collagen type I, collagen type V, and k-alpha 1 tubulin. Pre-existing antibodies against these lung-restricted antigens are prevalent in patients undergoing lung transplantation and have emerged as one of the predominant risk factors for primary graft dysfunction which limits short-term survival following lung transplantation. Additionally, LRA have been shown to predispose to chronic lung allograft rejection, the predominant cause of poor long-term survival. This review will discuss ongoing research into the mechanisms of development of LRA as well as the pathogenesis of associated lung allograft injury.

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.

Peripartum Cardiomyopathy: Current Options for Treatment and Cardiovascular Support

Peripartum cardiomyopathy is a rare form of acute heart failure but the major cause of all deaths in pregnant patients with heart failure. Improved survival rates in recent years, however, emphasize the importance of early recognition and initiation of heart failure treatment. This article, therefore, attempts to raise awareness among cardiac and obstetric anesthesiologists as well as intensivists of this often fatal diagnosis. This review summarizes theories of the pathophysiology and outcome of peripartum cardiomyopathy. Based on the most recent literature, it further outlines diagnostic criteria and treatment options including medical management, mechanical circulatory support devices, and heart transplantation. Earlier recognition of this rare condition and a new generation of mechanical circulatory devices has contributed to the improved outcome. More frequently, patients in cardiogenic shock who fail medical management are successfully bridged to recovery on extracorporeal circulatory devices or survive with a long-lasting implantable ventricular assist device. The outcome of transplanted patients with peripartum cardiomyopathy, however, is worse compared to other recipients of heart transplants and warrants further investigation in the future.

Mast cells participate in allograft rejection: can IL-37 play an inhibitory role?

OBJECTIVE

The aim of this study was to evaluate the role of mast cells (MCs) in allograft rejection, eventually inhibited by IL-37. Immune cells including MCs participate in allograft rejection by generating IL-1, IL-33, TNF and other cytokines.

METHODS

We evaluated allograft rejection on the experience of our experimental data and using the relevant literature.

RESULTS

MCs are involved in initiation and regulation of innate and adaptive immune responses-pathways. MCs are important pro-inflammatory cells which express high-affinity receptor FceRI and can be activated by IgE and some pro-inflammatory cytokines, such as IL-1 and IL-33. The cross-linkage of high affinity IgE receptor on MCs by antigen ligation has a crucial role in allergy, asthma, anaphylaxis, cancer and allograft rejection. MCs mediate immunity in organ transplant, leading to the activation of allospecific T cells implicated in the rejection and generate pro-inflammatory cytokines/chemokines. IL-1 pro-inflammatory cytokine family members released by MCs mediate allograft rejection and inflammation. IL-37 is also an IL-1 family member generated by macrophage cell line in small amounts, which binds to IL-18Rα and produces an anti-inflammatory effect. IL-37 provokes the inhibition of TLR signaling, TLR-induced mTOR and (MyD88)-mediated responses, suppressing pro-inflammatory IL-1 family members and increasing IL-10.

CONCLUSION

IL-37 inhibition offers the opportunity to immunologically modulate MCs, by suppressing their production of IL-1 family members and reducing the risk of allograft rejection, resulting as a potential good therapeutic new cytokine. Here, we report the relationship between inflammatory MCs, allograft rejection and pro-inflammatory and anti-inflammatory IL-37.

The role of exosomes in allograft immunity

Extracellular vesicles are emerging as potent vehicles of intercellular communication. In this review, we focus on a subclass of extracellular vesicles called exosomes. Previously considered an unimportant catch-all, exosomes have recently been recognized for their role in various diseases and their potential for therapeutic use. We have examined the role of exosomes after human lung transplantation and have delineated the composition of circulating exosomes isolated from lung transplant recipients diagnosed with acute and chronic rejection, primary graft dysfunction, and respiratory viral infection. The presence of lung-associated self-antigens (K-alpha 1 Tubulin and collagen V) and mismatched donor HLA in exosomes isolated from lung transplant recipients signifies that these exosomes originated in the transplanted lungs, and therefore dramatically affect transplant biology and immune pathways. Exosomes released from transplanted organs also carry other proteins, costimulatory molecules, and nucleic acids. Therefore, these molecules may be used as biomarkers for allograft rejection and immunity.

Acute rejection

Despite induction immunosuppression and the use of aggressive maintenance immunosuppressive regimens, acute allograft rejection following lung transplantation is still a problem with important diagnostic and therapeutic challenges. As well as causing early graft loss and mortality, acute rejection also initiates the chronic alloimmune responses and airway-centred inflammation that predispose to bronchiolitis obliterans syndrome (BOS), also known as chronic lung allograft dysfunction (CLAD), which is a major source of morbidity and mortality after lung transplantation. Cellular responses to human leukocyte antigens (HLAs) on the allograft have traditionally been considered the main mechanism of acute rejection, but the influence of humoral immunity is increasingly recognised. As with other several other solid organ transplants, antibody-mediated rejection (AMR) is now a well-accepted and distinct clinical entity in lung transplantation. While acute cellular rejection (ACR) has defined histopathological criteria, transbronchial biopsy is less useful in AMR and its diagnosis is complicated by challenges in the measurement of antibodies directed against donor HLA, and a determination of their significance. Increasing awareness of the importance of non-HLA antigens further clouds this issue. Here, we review the pathophysiology, diagnosis, clinical presentation and treatment of ACR and AMR in lung transplantation, and discuss future potential biomarkers of both processes that may forward our understanding of these conditions.

Regenerative immunology: the immunological reaction to biomaterials

Regenerative medicine promises to meet two of the most urgent needs of modern organ transplantation, namely immunosuppression-free transplantation and an inexhaustible source of organs. Ideally, bioengineered organs would be manufactured from a patient's own biomaterials-both cells and the supporting scaffolding materials in which cells would be embedded and allowed to mature to eventually regenerate the organ in question. While some groups are focusing on the feasibility of this approach, few are focusing on the immunogenicity of the scaffolds that are being developed for organ bioengineering purposes. This review will succinctly discuss progress in the understanding of immunological characteristics and behavior of different scaffolds currently under development, with emphasis on the extracellular matrix scaffolds obtained decellularized animal or human organs which seem to provide the ideal template for bioengineering purposes.

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.