Evaluation of peripheral blood CD4 and CD8 lymphocyte subsets, CD69 expression and histologic rejection grade as diagnostic markers for the presence of cardiac allograft rejection

Cardiomyocytic cyclic GMP-AMP synthase is critical for the induction of experimental cardiac graft rejection

OBJECTIVE

During cardiac transplantation, cellular injury and DNA damage can result in the accumulation of cytosolic double-stranded DNA (dsDNA), which can activate the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon gene (STING) signaling pathway and thus induce multiple proinflammatory responses. However, the role of the cGAS-STING pathway in cardiac transplantation remains unclear. This study explored the role of cardiomyocytic cGAS in mouse heart transplantation during the ischemia/reperfusion and rejection processes.

METHODS AND RESULTS

Cytosolic dsDNA accumulation and cGAS-STING signaling pathway component upregulation were observed in the grafts posttransplantation. The use of cGAS-deficient donor tissues led to significantly prolonged graft survival. The underlying mechanisms involved decreased expression and phosphorylation of downstream proteins, including TANK binding kinase 1 and nuclear factor κB. In parallel, notably diminished expression levels of various proinflammatory cytokines were observed. Accordingly, substantially decreased proportions of macrophages (CD11b+F4/80+) and CD8+ T cells were observed in the spleen. The activation of CD8+ T cells (CD8+CD69+) within the graft and the proportion of effector memory (CD44highCD62Llow) lymphocytes in the spleen were notably decreased. Treatment with the cGAS inhibitor Ru.521 led to significantly prolonged graft survival.

CONCLUSIONS

Cardiomyocytic cGAS plays a critical role by sensing cytosolic dsDNA during cardiac transplantation and could serve as a potential therapeutic target to prevent graft rejection.

Immediate major dynamic changes in the T- and NK-cell subset composition after cardiac transplantation

Early kinetics of lymphocyte subsets involved in tolerance and rejection following heart transplantation (HTx) are barely defined. Here, we aimed to delineate the early alloimmune response immediately after HTx. Therefore, blood samples from 23 heart-transplanted patients were collected before (pre-), immediately (T0), 24 hours (T24), and 3 weeks (3 wks) after HTx. Immunophenotyping was performed using flow cytometry. A significant increase was detected for terminally differentiated (TEMRA) CD4+ or CD8+ T cells and CD56dim CD16+ NK cells immediately after HTx linked to a decrease in naïve CD8+ and CM CD4+ T as well as CD56bright CD16- NK cells, returning to baseline levels at T24. More detailed analyses revealed increased CD69+ CD25- and diminished CD69- CD25- CD4+ or CD8+ T-cell proportions at T0 associated with decreasing S1PR1 expression. Passenger T and NK cells were found at low frequencies only in several patients at T0 and did not correlate with lymphocyte alterations. Collectively, these results suggest an immediate, transient shift toward memory T and NK cells following HTx. Opposite migratory properties of naïve versus memory T and NK cells occurring in the early phase after HTx could underlie these observations and may impinge on the development of allo-specific immune responses.

PD-1 expression in transbronchial biopsies of lung transplant recipients is a possible early predictor of rejection

Introduction

Chronic lung allograft dysfunction (CLAD) is the main cause of the reduced survival of lung transplanted (LTx) patients. The possible role of immune checkpoint molecules in establishing tolerance has been scarcely investigated in the setting of lung transplantation.

Methods

We conducted a retrospective, observational pilot study on a consecutive series of transbronchial cryobiopsies (TCB) obtained from 24 patients during LTx follow-up focusing on PD-1, one of the most investigated immune checkpoint molecules.

Results

Results showed that PD-1-expressing T lymphocytes were present in all TCB with a histological diagnosis of acute rejection (AR; 9/9), but not in most (11/15) of the TCB not resulting in a diagnosis of AR (p=0.0006). Notably, the presence of PD-1-expressing T lymphocytes in TCB resulted in a 10-times higher risk of developing chronic lung allograft dysfunction (CLAD), the main cause of the reduced survival of lung transplanted patients, thus being associated with a clearly worst clinical outcome.

Discussion

Results of this pilot study indicate a central role of PD-1 in the development of AR and its evolution towards CLAD and suggest that the evaluation of PD-1-expressing lymphocytes in TCB could offer a prognostic advantage in monitoring the onset of AR in patients who underwent lung transplantation.

Characterization of decellularized implants for ECM integrity and immune response elicitation

Biological scaffold is a popular choice for the preparation of tissue-engineered organs and has the potential to address donor shortages in clinics. However, biological scaffolds prepared by physical or chemical agents cause damage to the extracellular matrix by potentially inducing immune responses after implantation. The current study explores the fate of the decellularized scaffolds using a cocktail of chemicals following implantation without using immunosuppressants. Using the syngeneic (Lewis male- Lewis female) and allogeneic (Brown Norway male- Lewis female) models and different tissue routes (subcutaneous vs omentum) for implantation, we applied in-depth quantitative proteomics, genomics along with histology and quantitative image analysis tools to comprehensively describe and compare the proteins following decellularization and post-implantation. Our data helped to identify any alteration post decullarization as well implantation. We could also monitor route-specific modulation of the Extracellular matrix (ECM) and regulation of the immune responses (macrophage and T cells) following implantation. The current approach opens up the possibility to monitor the fate of biological scaffolds in terms of the ECM and immune response against the implants. In addition, the identification of different routes helped us to identify differential immune responses against the implants. This study opens up the potential to identify the changes associated with chemical decellularization both pre and post-implantation, which could further help to promote research in this direction.

Immune Checkpoints Expression in Chronic Lung Allograft Rejection

Chronic lung allograft dysfunction (CLAD) is the main cause of poor survival and low quality of life of lung transplanted patients. Several studies have addressed the role of dendritic cells, macrophages, T cells, donor specific as well as anti-HLA antibodies, and interleukins in CLAD, but the expression and function of immune checkpoint molecules has not yet been analyzed, especially in the two CLAD subtypes: BOS (bronchiolitis obliterans syndrome) and RAS (restrictive allograft syndrome). To shed light on this topic, we conducted an observational study on eight consecutive grafts explanted from patients who received lung re-transplantation for CLAD. The expression of a panel of immune molecules (PD1/CD279, PDL1/CD274, CTLA4/CD152, CD4, CD8, hFoxp3, TIGIT, TOX, B-Cell-Specific Activator Protein) was analyzed by immunohistochemistry in these grafts and in six control lungs. Results showed that RAS compared to BOS grafts were characterized by 1) the inversion of the CD4/CD8 ratio; 2) a higher percentage of T lymphocytes expressing the PD-1, PD-L1, and CTLA4 checkpoint molecules; and 3) a significant reduction of exhausted PD-1-expressing T lymphocytes (PD-1^pos/TOX^pos) and of exhausted Treg (PD-1^pos/FOXP3^pos) T lymphocytes. Results herein, although being based on a limited number of cases, suggest a role for checkpoint molecules in the development of graft rejection and offer a possible immunological explanation for the worst prognosis of RAS. Our data, which will need to be validated in ampler cohorts of patients, raise the possibility that the evaluation of immune checkpoints during follow-up offers a prognostic advantage in monitoring the onset of rejection, and suggest that the use of compounds that modulate the function of checkpoint molecules could be evaluated in the management of chronic rejection in LTx patients.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

High proportion of CD95(+) and CD38(+) in cultured CD8(+) T cells predicts acute rejection and infection, respectively, in kidney recipients

The aim of this study was to find noninvasive T-cell markers able to predict rejection or infection risk after kidney transplantation. We prospectively examined T-lymphocyte subsets after cell culture stimulation (according to CD38, CD69, CD95, CD40L, and CD25 expression) in 79 first graft recipients from four centers, before and after transplantation. Patients were followed up for one year. Patients who rejected within month-1 (n=10) showed high pre-transplantation and week-1 post-transplantation percentages of CD95(+), in CD4(+) and CD8(+) T-cells (P<0.001 for all comparisons). These biomarkers conferred independent risk for early rejection (HR:5.05, P=0.061 and HR:75.31, P=0.004; respectively). The cut-off values were able to accurately discriminate between rejectors and non-rejectors and Kaplan-Meier curves showed significantly different free-of-rejection time rates (P<0.005). Patients who rejected after the month-1 (n=4) had a higher percentage of post-transplantation CD69(+) in CD8(+) T-cells than non-rejectors (P=0.002). Finally, patients with infection (n=41) previously showed higher percentage of CD38(+) in CD8(+) T-cells at all post-transplantation times evaluated, being this increase more marked in viral infections. A cut-off of 59% CD38(+) in CD8(+) T-cells at week-1, week-2 and month-2 reached 100% sensitivity for the detection of subsequent viral infections. In conclusion, predictive biomarkers of rejection and infection risk after transplantation were detected that could be useful for the personalized care of kidney recipients.

The role of immunological biomarkers in cardiac rejection

PURPOSE OF REVIEW

To summarize the promises and limitations of candidate noninvasive immunological biomarkers in cardiac rejection, with a special focus on the chemokine CXCL10, as a pretransplant predictive marker of early heart acute rejection. Potential issues for transfer from research to the clinic are addressed.

RECENT FINDINGS

Early changes of immune biomolecules in peripheral blood, reflecting graft or heart recipient's immune status, are candidate biomarkers able to diagnose or predict cardiac rejection, ideally giving an opportunity to intervene before heart failure occurs. The support of robust analytical methodologies is necessary for the transition from biomarker discovery to clinical implementation.

SUMMARY

Cardiac rejection represents the main problem after heart transplantation. Endomyocardial biopsy, although invasive and not risk free, is the gold-standard procedure for rejection monitoring. Noninvasive heart damage biomarkers manifest substantially after rejection occurrence. The goal is to detect graft injury at the earliest possible stage in disease initiation. Some biomolecules associated with the early immune response to cardiac allograft retain the power to be diagnostic and, even better, predictive of acute rejection, as in the case of pretransplant CXCL10 serum level. Multicenter studies for assay validation and standardization, integrated analysis of multiple biomarkers, and cost-effectiveness evaluation are mandatory efforts.

Is CD69 an effective brake to control inflammatory diseases?

Early studies described CD69 as a leukocyte activation marker, and suggested its involvement in the activation of different leukocyte subsets as well as in the pathogenesis of chronic inflammation. However, recent investigations have showed that CD69 knockout mice exhibit an enhanced or reduced susceptibility to different experimental models of inflammatory diseases, including those mediated by T helper 17 (Th17) lymphocytes. In this regard, the expression of CD69, both in Th17 lymphocytes and by a subset of regulatory T cells, has an important role in the control of the immune response and the inflammatory phenomenon. Therefore, different evidence indicates that CD69 exerts a complex immunoregulatory role in humans, and that it could be considered as a target molecule for the therapy of immune-mediated diseases.

Mechanical compliance and immunological compatibility of fixative-free decellularized/cryopreserved human pericardium

BACKGROUND

The pericardial tissue is commonly used to produce bio-prosthetic cardiac valves and patches in cardiac surgery. The procedures adopted to prepare this tissue consist in treatment with aldehydes, which do not prevent post-graft tissue calcification due to incomplete xeno-antigens removal. The adoption of fixative-free decellularization protocols has been therefore suggested to overcome this limitation. Although promising, the decellularized pericardium has not yet used in clinics, due to the absence of proofs indicating that the decellularization and cryopreservation procedures can effectively preserve the mechanical properties and the immunologic compatibility of the tissue.

PRINCIPAL FINDINGS

The aim of the present work was to validate a procedure to prepare decellularized/cryopreserved human pericardium which may be implemented into cardiovascular homograft tissue Banks. The method employed to decellularize the tissue completely removed the cells without affecting ECM structure; furthermore, uniaxial tensile loading tests revealed an equivalent resistance of the decellularized tissue to strain, before and after the cryopreservation, in comparison with the fresh tissue. Finally, immunological compatibility, showed a minimized host immune cells invasion and low levels of systemic inflammation, as assessed by tissue transplantation into immune-competent mice.

CONCLUSIONS

Our results indicate, for the first time, that fixative-free decellularized pericardium from cadaveric tissue donors can be banked according to Tissue Repository-approved procedures without compromising its mechanical properties and immunological tolerance. This tissue can be therefore treated as a safe homograft for cardiac surgery.

Activation of peripheral blood CD3(+) T-lymphocytes in patients with atrial fibrillation

Atrial fibrillation (AF) is a common disease with a poorly understood pathophysiological mechanism. Increasing evidence indicates that AF may be associated with immunologic inflammation responses, but it remains unclear whether activation of peripheral blood CD3(+) T-lymphocytes plays a role in the pathogenesis of AF. The aim of this study was to evaluate this phenomenon. Fifty paroxysmal AF patients and 56 persistent AF patients who underwent successful electrical cardioversion were enrolled. The percentages of CD69 and human leukocyte antigen DR (HLA-DR) positive peripheral blood CD3(+) T-lymphocytes, which indicate T-lymphocyte activation, were examined by flow cytometric analysis in the patients and 51 healthy controls. The patient groups had higher levels of CD69 and HLA-DR than the healthy controls. During the 3-month follow-up, 37 patients had recurrence of AF (recurrence group) and 50 patients remained in sinus (sinus group). The CD69 and HLA-DR levels in the sinus group were all significantly down-regulated at follow-up compared with before cardioversion. However, there were no statistically significant differences between the CD69 and HLA-DR levels in the recurrence group at follow-up and before cardioversion. Our findings suggest that activation of peripheral blood CD3(+) T-lymphocytes was associated with AF, and might be a diagnostic or therapeutic marker.

Peripheral blood sampling for the detection of allograft rejection: biomarker identification and validation

Currently, acute allograft rejection can only be detected reliably by deterioration of graft function confirmed by allograft biopsy. A huge drawback of this method of diagnosis is that substantial organ damage has already taken place at the time that rejection is diagnosed. Discovering and validating noninvasive biomarkers that predict acute rejection, and chronic allograft dysfunction, is of great importance. Many studies have investigated changes in the peripheral blood in an attempt to find biomarkers that reflect changes in the graft directly or indirectly. Herein, we will review the promises and limitations of the peripheral blood biomarkers that have been described in the literature so far.

Immunological study of allogeneic mesenchymal stem cells during bone formation

Autologous mesenchymal stem cells (MSCs) are limited in their clinical application because tissue-engineered bone cannot be pre-fabricated. Allogeneic MSCs are readily available but carry the risk of transplant rejection. It is not yet clear whether allogeneic MSCs can induce a rejection response during bone formation. In this study, two strains of genetically unmatched mini-pigs were used as experimental animals to study the immunological changes in MSCs in vitro and in vivo when generating bone. Mini-pig MSCs showed low immunogenicity during osteogenesis both in vitro and in vivo, indicating that allogeneic MSCs had little or no immunogenicity in osteosis. In conclusion, allogeneic MSCs are an important source of seed cells for the tissue engineering of bone. This favours the clinical application of pre-constructed tissue-engineered bone.

Expansion and tissue infiltration of an allospecific CD4+CD25+CD45RO+IL-7Ralphahigh cell population in solid organ transplant recipients

It has been recently shown (Seddiki, N., B. Santner-Nanan, J. Martinson, J. Zaunders, S. Sasson, A. Landay, M. Solomon, W. Selby, S.I. Alexander, R. Nanan, et al. 2006. J. Exp. Med. 203:1693–1700.) that the expression of interleukin (IL) 7 receptor (R) α discriminates between two distinct CD4 T cell populations, both characterized by the expression of CD25, i.e. CD4 regulatory T (T reg) cells and activated CD4 T cells. T reg cells express low levels of IL-7Rα, whereas activated CD4 T cells are characterized by the expression of IL-7Rα^high. We have investigated the distribution of these two CD4 T cell populations in 36 subjects after liver and kidney transplantation and in 45 healthy subjects. According to a previous study (Demirkiran, A., A. Kok, J. Kwekkeboom, H.J. Metselaar, H.W. Tilanus, and L.J. van der Laan. 2005. Transplant. Proc. 37:1194–1196.), we observed that the T reg CD25⁺CD45RO⁺IL-7Rα^low cell population was reduced in transplant recipients (P < 0.00001). Interestingly, the CD4⁺CD25⁺CD45RO⁺IL-7Rα^high cell population was significantly increased in stable transplant recipients compared with healthy subjects (P < 0.00001), and the expansion of this cell population was even greater in patients with documented humoral chronic rejection compared with stable transplant recipients (P < 0.0001). The expanded CD4⁺CD25⁺CD45RO⁺IL-7Rα^high cell population contained allospecific CD4 T cells and secreted effector cytokines such as tumor necrosis factor α and interferon γ, thus potentially contributing to the mechanisms of chronic rejection. More importantly, CD4⁺IL-7Rα⁺and CD25⁺IL-7Rα⁺ cells were part of the T cell population infiltrating the allograft of patients with a documented diagnosis of chronic humoral rejection. These results indicate that the CD4⁺CD25⁺IL-7Rα⁺ cell population may represent a valuable, sensitive, and specific marker to monitor allospecific CD4 T cell responses both in blood and in tissues after organ transplantation.

Viral IL-10-mediated immune regulation in pancreatic islet transplantation

Protection of transplanted pancreatic islet grafts in recipients with autoimmune diabetes depends on the suppression of autoimmune recurrence and allogeneic rejection. The aim of this study was to investigate the efficiency of viral IL-10 gene delivery in the prevention of autoimmune recurrence following islet transplantation. We evaluated the effectiveness of a systemically delivered adeno-associated viral vector (AAV vIL-10) carrying viral IL-10 in protecting islet engraftment. We observed significant prolongation of graft survival after treatment with AAV vIL-10 when using islets from donors lacking autoimmunity. We found that the mechanism of vIL-10-mediated protection was associated with suppression of T cell activation and that donor immune cells that were simultaneously transferred with the islet grafts could induce autoimmune recurrence. AAV vIL-10 gene transfer suppressed previously activated T cells and protected grafted islets from autoimmune-mediated destruction. We conclude that vIL-10 can regulate autoimmune activity and that transfer of its gene may have potential for therapeutic islet transplantation.

Enhanced donor-specific alloreactivity occurs independently of immunosuppression in children with early liver rejection

To determine whether early acute cellular rejection (ACR) is associated with sub-optimal immunosuppression in children with liver transplants (LTx).

METHODS

Twenty-five children with primary LTx after pre-transplant rabbit anti-thymocyte globulin (rATG), and steroid-free tacrolimus (TAC) were evaluated. Mitogen-stimulated T- and B-cell responses and mixed lymphocyte response to donor and third-party antigens were performed at several time points between two consecutive TAC doses. TAC concentrations (C) associated with half-maximal effect (EC(50)) on lymphocytes was determined by pharmacodynamic equations.

RESULTS

Mean age was 7.2 +/- 6.2 years, mean time to lymphocyte function studies was 25 +/- 19 days. Acute rejection occurred at a mean interval of 31 +/- 19 days after LTx. Rejectors (n = 16) demonstrated significantly higher EC(50) of TAC for the intra-cellular IFN-gamma in T cells (p = 0.005) and its CD8+ sub-population (p = 0.027) as well as the co-stimulatory/activation receptor CD54 on B cells (p = 0.0001). The response of recipient lymphocytes to donor antigen was significantly higher in rejectors, compared with non-rejectors (p = 0.015). The patient groups demonstrated no differences in third-party MLR, or in C of TAC.

CONCLUSIONS

Independent of the amount of immunosuppressant, ACR of liver allografts in children is associated with enhanced donor-specific alloreactivity. This is accompanied by a cytotoxic T-cell sub-population with increased requirement for TAC.