Immunomodulation of T cell-mediated alloimmunity by proximity to endothelial cells under the mammalian target of rapamycin blockade

Endothelial cells (ECs) are an initial barrier between vascularized organ allografts and the host immune system and are thus well positioned to initiate and influence alloimmune rejection. The mammalian target of rapamycin inhibitor rapamycin is known to inhibit T cell activation and attenuate acute allograft rejection. It also has numerous effects on ECs. We hypothesized that A mammalian target of rapamycin blockade might directly alter EC alloimmunogenicity and reduce alloimmune responses independent of its effects on T cell function. Here we report that rapamycin treatment modulates EC coinhibitory ligand expression and alters cytokine/chemokine production. It alters the EC transcriptome broadly associated with negative regulation of immune responses. Rapamycin-treated ECs suppress EC-specific T cell proliferation independent of programmed cell death 1/programmed death-ligand interaction and inhibit T cells responding to adjacent allogeneic cells in a contact-independent manner via secreted inhibitory mediators above 10 kDa. The T cell hyporesponsiveness induced by rapamycin-pretreated ECs was rescued by exogenous interleukin 2. Preexposing donor hearts to rapamycin improves the effect of B7 costimulation blockade in prolonging heart allograft survival in a major histocompatibility complex-mismatched mouse model. Our results indicate that rapamycin-treated ECs have reduced alloimmunogenicity and created a local, contact-independent environment that limits T cell alloreactivity via anergy induction and improves the efficacy of B7 costimulation blockade.

Re-Evaluating the Transplant Glomerulopathy Lesion-Beyond Donor-Specific Antibodies

There have been significant advances in short-term outcomes in renal transplantation. However, longer-term graft survival has improved only minimally. After the first post-transplant year, it has been estimated that chronic allograft damage is responsible for 5% of graft loss per year. Transplant glomerulopathy (TG), a unique morphologic lesion, is reported to accompany progressive chronic allograft dysfunction in many cases. While not constituting a specific etiologic diagnosis, TG is primarily considered as a histologic manifestation of ongoing allo-immune damage from donor-specific anti-HLA alloantibodies (DSA). In this review article, we re-evaluate the existing literature on TG, with particular emphasis on the role of non-HLA-antibodies and complement-mediated injury, cell-mediated immune mechanisms, and early podocyte stress in the pathogenesis of Transplant Glomerulopathy.

Outcome-based Risk Assessment of Non-HLA Antibodies in Heart Transplantation: A Systematic Review

BACKGROUND

Current monitoring after heart transplantation (HT) employs repeated invasive endomyocardial biopsies (EMB). Although positive EMB confirms rejection, EMB fails to predict impending, subclinical, or EMB-negative rejection events. While non-human leukocyte antigen (non-HLA) antibodies have emerged as important risk factors for antibody-mediated rejection after HT, their use in clinical risk stratification has been limited. A systematic review of the role of non-HLA antibodies in rejection pathologies has the potential to guide efforts to overcome deficiencies of EMB in rejection monitoring.

METHODS

Databases were searched to include studies on non-HLA antibodies in HT recipients. Data collected included the number of patients, type of rejection, non-HLA antigen studied, association of non-HLA antibodies with rejection, and evidence for synergistic interaction between non-HLA antibodies and donor-specific anti-human leukocyte antigen antibody (HLA-DSA) responses.

RESULTS

A total of 56 studies met the inclusion criteria. Strength of evidence for each non-HLA antibody was evaluated based on the number of articles and patients in support versus against their role in mediating rejection. Importantly, despite previous intense focus on the role of anti-major histocompatibility complex class I chain-related gene A (MICA) and anti-angiotensin II type I receptor antibodies (AT1R) in HT rejection, evidence for their involvement was equivocal. Conversely, the strength of evidence for other non-HLA antibodies supports that differing rejection pathologies are driven by differing non-HLA antibodies.

CONCLUSIONS

This systematic review underscores the importance of identifying peri-HT non-HLA antibodies. Current evidence supports the role of non-HLA antibodies in all forms of HT rejection. Further investigations are required to define the mechanisms of action of non-HLA antibodies in HT rejection.

Relevance of donor-specific HLA antibodies in hematopoietic cell transplantation

Advances in hematopoietic cell transplantation have expanded the use of alternative donors such as haploidentical family donors or mismatched unrelated donors. However, donor-specific HLA antibodies (DSA) have been recognized as a significant risk factor of primary graft failure after HLA incompatible transplantation. Therefore, screening for HLA antibodies and taking DSA into consideration in the process of donor search play an increasingly important role in donor selection. If an HLA compatible donor is not available, desensitization may enable a successful transplantation. In this review, we describe the currently most widely used methods for HLA antibody detections including their pitfalls. In addition, we summarize the results of the studies on the impact of preformed DSA on transplant outcomes and their treatment options. Many more and larger studies are needed to clarify laboratory issues as well as immunological and clinical aspects in the management of DSA.

Human leukocyte antigen class I antibody-activated endothelium promotes CD206+ M2 macrophage polarization and MMP9 secretion through TLR4 signaling and P-selectin in a model of antibody-mediated rejection and allograft vasculopathy

HLA donor-specific antibodies (DSA) elicit alloimmune responses against the graft vasculature, leading to endothelial cell (EC) activation and monocyte infiltration during antibody-mediated rejection (AMR). AMR promotes chronic inflammation and remodeling, leading to thickening of the arterial intima termed transplant vasculopathy or cardiac allograft vasculopathy (CAV) in heart transplants. Intragraft-recipient macrophages serve as a diagnostic marker in AMR; however, their polarization and function remain unclear. In this study, we utilized an in vitro Transwell coculture system to explore the mechanisms of monocyte-to-macrophage polarization induced by HLA I DSA-activated ECs. Anti-HLA I (IgG or F(ab')2) antibody-activated ECs induced the polarization of M2 macrophages with increased CD206 expression and MMP9 secretion. However, inhibition of TLR4 signaling or PSGL-1-P-selectin interactions significantly decreased both CD206 and MMP9. Monocyte adherence to Fc-P-selectin coated plates induced M2 macrophages with increased CD206 and MMP9. Moreover, Fc-receptor and IgG interactions synergistically enhanced active-MMP9 in conjunction with P-selectin. Transcriptomic analysis of arteries from DSA+CAV+ rejected cardiac allografts and multiplex-immunofluorescent staining illustrated the expression of CD68+CD206+CD163+MMP9+ M2 macrophages within the neointima of CAV-affected lesions. These findings reveal a novel mechanism linking HLA I antibody-activated endothelium to the generation of M2 macrophages which secrete vascular remodeling proteins contributing to AMR and CAV pathogenesis.

Assessing the role of phosphorylated S6 ribosomal protein in the pathological diagnosis of pulmonary antibody-mediated rejection

BACKGROUND

Pulmonary antibody-mediated rejection is still a challenging diagnosis as C4d immunostaining has poor sensitivity. Previous studies have indicated that the phosphorylated S6 ribosomal protein, a component of the mammalian target of rapamycin (mTOR) pathway, is correlated with de novo donor-specific antibodies in lung transplantation. The objective of this study was to evaluate the phosphorylation of S6 ribosomal protein as a surrogate for antibody-mediated rejection diagnosis in lung transplant patients.

METHODS

This multicentre retrospective study analyzed transbronchial biopsies from 216 lung transplanted patients, 114 with antibody-mediated rejection and 102 without (19 with acute cellular rejection, 17 with ischemia/reperfusion injury, 18 with infection, and 48 without post-transplant complications). Immunohistochemistry was used to quantify phosphorylated S6 ribosomal protein expression in macrophages, endothelium, epithelium, and inter-pathologist agreement was assessed.

RESULTS

Median phosphorylated S6 ribosomal protein expression values were higher in antibody-mediated rejection cases than in controls for all cell components, with the highest sensitivity in macrophages (0.9) and the highest specificity in endothelial expression (0.8). The difference was mainly significant in macrophages compared to other post-lung transplantation complications. Inter-pathologist agreement was moderate for macrophages and endothelium, with higher agreement when phosphorylated S6 ribosomal protein expression was dichotomized into positive/negative. The inclusion of phosphorylated S6 ribosomal protein in the diagnostic algorithm could have increased antibody-mediated rejection certainty levels by 25%.

CONCLUSIONS

The study supports the role of the mTOR pathway in antibody-mediated rejection-related graft injury and suggests that tissue phosphorylation of S6 ribosomal protein could be a useful surrogate for a more accurate pathological diagnosis of lung antibody-mediated rejection.

Lipophilic Statins Inhibit YAP Nuclear Localization, Coactivator Activity, and Migration in Response to Ligation of HLA Class I Molecules in Endothelial Cells: Role of YAP Multisite Phosphorylation

Solid-organ transplant recipients exhibiting HLA donor-specific Abs are at risk for graft loss due to chronic Ab-mediated rejection. HLA Abs bind HLA molecules expressed on the surface of endothelial cells (ECs) and induce intracellular signaling pathways, including the activation of the transcriptional coactivator yes-associated protein (YAP). In this study, we examined the impact of lipid-lowering drugs of the statin family on YAP localization, multisite phosphorylation, and transcriptional activity in human ECs. Exposure of sparse cultures of ECs to cerivastatin or simvastatin induced striking relocalization of YAP from the nucleus to the cytoplasm and inhibited the expression of the YAP/TEA domain DNA-binding transcription factor-regulated genes connective tissue growth factor and cysteine-rich angiogenic inducer 61. In dense cultures of ECs, statins prevented YAP nuclear import and expression of connective tissue growth factor and cysteine-rich angiogenic inducer 61 stimulated by the mAb W6/32 that binds HLA class I. Exposure of ECs to either cerivastatin or simvastatin completely blocked the migration of ECs stimulated by ligation of HLA class I. Exogenously supplied mevalonic acid or geranylgeraniol reversed the inhibitory effects of statins on YAP localization either in low-density ECs or high-density ECs challenged with W6/32. Mechanistically, cerivastatin increased the phosphorylation of YAP at Ser127, blunted the assembly of actin stress fiber, and inhibited YAP phosphorylation at Tyr357 in ECs. Using mutant YAP, we substantiated that YAP phosphorylation at Tyr357 is critical for YAP activation. Collectively, our results indicate that statins restrain YAP activity in EC models, thus providing a plausible mechanism underlying their beneficial effects in solid-organ transplant recipients.

HLA class II antibody activation of endothelial cells induces M2 macrophage differentiation in peripheral blood

BACKGROUND

Donor-specific human leukocyte antigen (HLA) class II antibodies (HLA-II Abs) combined with allogeneic endothelial cells (ECs) mediate high-risk rejection in kidney transplant patients. Macrophage accumulation is a significant histological feature of antibody-mediated rejection (AMR) in kidney transplant patients. Here, we further investigated the effect of HLA-II Abs on macrophage phenotypes to provide theoretical basis for clinical treatment of AMR.

METHODS

We prepared an experimental model containing HLA-II Ab-stimulated microvascular ECs and peripheral blood mononuclear cells (PBMCs) co-culture and explored the potential relationship of HLA-II Ab, ECs activation, and macrophage differentiation. Immune phenotype of macrophage subsets was analyzed and quantified by flow cytometry. HLA-II Ab activation of ECs induces M2 macrophage differentiation signal pathways which were investigated by qPCR and western blotting.

RESULTS

The stimulation of ECs by F(ab')₂ fragment of HLA-II Abs led to phosphorylation of PI3K, Akt, and mTOR, which mediated IL-10, ICAM-1, VCAM-1 secretion. The enhanced ICAM-1 and IL-10 promoted the migration of PBMCs and their differentiation into CD68⁺ and CD163⁺ (M2-type) macrophages, respectively, but not CD86⁺ macrophages.

CONCLUSION

These findings revealed the PI3K/Akt/mTOR signal pathways activated by HLA-II Abs in ECs and the immune regulation ability of HLA-II Abs to induce PBMC differentiation.

Phosphorylation of S6RP in peritubular capillaries of kidney grafts and circulating HLA donor-specific antibodies

Antibody-mediated rejection (ABMR) caused by donor-specific HLA-antibodies (DSA) is a mediator of allograft loss after kidney transplantation (KT). DSA can activate microvascular endothelium damage through the mTOR pathway. In this study we assessed the mTOR pathway activation by DSA in KT with ABMR (ABMR + DSA+) compared to controls (ABMR−DSA−), biopsies with ABMR changes without DSA (ABMR + DSA−) and DSA without ABMR changes (ABMR−DSA+), and the potential modulation by mTOR inhibitors (mTORi). We evaluated 97 biopsies: 31 ABMR + DSA+, 33 controls ABMR-DSA−, 16 ABMR + DSA−, and 17 ABMR-DSA+ cases. Regarding immunosuppression of full ABMR + DSA+ and controls, 21 biopsies were performed under mTORi treatment (11 of them ABMR + DSA+ cases) and 43 without mTORi (20 of them ABMR + DSA+) so as to explore its effect on the mTOR pathway. Biopsies were stained for C4d, Ki67, and phosphorylated (p) S6RP, ERK, and mTOR by immunohistochemistry. Labeling was graded according to peritubular capillary staining. ABMR biopsies showed significantly higher C4d, p-S6RP, and Ki67 staining in peritubular capillaries (PTC) compared to controls, and light differences in p-ERK or p-mTOR. mTORi treatment did not modify p-S6RP, p-mTOR, and p-ERK staining. Diffuse p-S6RP in PTC in the biopsies significantly associated with circulating HLA-DSA independently of graft rejection, and with worse death-censored graft survival. These findings suggest that activation of endothelium through the mTOR pathway evidence different mechanisms of damage in ABMR + DSA+ and ABMR + DSA− despite similar histological injury.

Cross-Talk between HLA Class I and TLR4 Mediates P-Selectin Surface Expression and Monocyte Capture to Human Endothelial Cells

Donor-specific HLA Abs contribute to Ab-mediated rejection (AMR) by binding to HLA molecules on endothelial cells (ECs) and triggering intracellular signaling, leading to EC activation and leukocyte recruitment. The molecular mechanisms involving donor-specific HLA Ab-mediated EC activation and leukocyte recruitment remain incompletely understood. In this study, we determined whether TLRs act as coreceptors for HLA class I (HLA I) in ECs. We found that human aortic ECs express TLR3, TLR4, TLR6, and TLR10, but only TLR4 was detected on the EC surface. Consequently, we performed coimmunoprecipitation experiments to examine complex formation between HLA I and TLR4. Stimulation of human ECs with HLA Ab increased the amount of complex formation between HLA I and TLR4. Reciprocal coimmunoprecipitation with a TLR4 Ab confirmed that the crosslinking of HLA I increased complex formation between TLR4 and HLA I. Knockdown of TLR4 or MyD88 with small interfering RNAs inhibited HLA I Ab-stimulated P-selectin expression, von Willebrand factor release, and monocyte recruitment on ECs. Our results show that TLR4 is a novel coreceptor for HLA I to stimulate monocyte recruitment on activated ECs. Taken together with our previous published results, we propose that HLA I molecules form two separate signaling complexes at the EC surface, that is, with TLR4 to upregulate P-selectin surface expression and capture of monocytes to human ECs and integrin β4 to induce mTOR-dependent firm monocyte adhesion via ICAM-1 clustering on ECs, two processes implicated in Ab-mediated rejection.

Role of HLA-I Structural Variants and the Polyreactive Antibodies They Generate in Immune Homeostasis

Cell-surface HLA-I molecules consisting of β2-microglobulin (β2m) associated heavy chains (HCs), referred to as Face-1, primarily present peptides to CD8+ T-cells. HCs consist of three α-domains, with selected amino acid sequences shared by all alleles of all six isoforms. The cell-surface HLA undergoes changes upon activation by pathological conditions with the expression of β2m-free HCs (Face-2) resulting in exposure of β2m-masked sequences shared by almost all alleles and the generation of HLA-polyreactive antibodies (Abs) against them. Face-2 may homodimerize or heterodimerize with the same (Face-3) or different alleles (Face-4) preventing exposure of shared epitopes. Non-allo immunized males naturally carry HLA-polyreactive Abs. The therapeutic intravenous immunoglobulin (IVIg) purified from plasma of thousands of donors contains HLA-polyreactive Abs, admixed with non-HLA Abs. Purified HLA-polyreactive monoclonal Abs (TFL-006/007) generated in mice after immunizing with Face-2 are documented to be immunoregulatory by suppressing or activating different human lymphocytes, much better than IVIg. Our objectives are (a) to elucidate the complexity of the HLA-I structural variants, and their Abs that bind to both shared and uncommon epitopes on different variants, and (b) to examine the roles of those Abs against HLA-variants in maintaining immune homeostasis. These may enable the development of personalized therapeutic strategies for various pathological conditions.

B-cell response in solid organ transplantation

The transcriptional regulation of B-cell response to antigen stimulation is complex and involves an intricate network of dynamic signals from cytokines and transcription factors propagated from T-cell interaction. Long-term alloimmunity, in the setting of organ transplantation, is dependent on this B-cell response, which does not appear to be halted by current immunosuppressive regimens which are targeted at T cells. There is emerging evidence that shows that B cells have a diverse response to solid organ transplantation that extends beyond plasma cell antibody production. In this review, we discuss the mechanistic pathways of B-cell activation and differentiation as they relate to the transcriptional regulation of germinal center B cells, plasma cells, and memory B cells in the setting of solid organ transplantation.

Protection of transplants against antibody-mediated injuries: from xenotransplantation to allogeneic transplantation, mechanisms and therapeutic insights

Long-term allograft survival in allotransplantation, especially in kidney and heart transplantation, is mainly limited by the occurrence of antibody-mediated rejection due to anti-Human Leukocyte Antigen antibodies. These types of rejection are difficult to handle and chronic endothelial damages are often irreversible. In the settings of ABO-incompatible transplantation and xenotransplantation, the presence of antibodies targeting graft antigens is not always associated with rejection. This resistance to antibodies toxicity seems to associate changes in endothelial cells phenotype and modification of the immune response. We describe here these mechanisms with a special focus on endothelial cells resistance to antibodies. Endothelial protection against anti-HLA antibodies has been described in vitro and in animal models, but do not seem to be a common feature in immunized allograft recipients. Complement regulation and anti-apoptotic molecules expression appear to be common features in all these settings. Lastly, pharmacological interventions that may promote endothelial cell protection against donor specific antibodies will be described.

Engineered three-dimensional cardiac tissues maturing in a rotating wall vessel bioreactor remodel diseased hearts in rats with myocardial infarction

A rotating wall vessel (RWV) bioreactor was constructed for growing massive functional cardiac constructs to recover the function of a distressed rat heart. Three-dimensional cardiac tissues were engineered by seeding human-induced pluripotent stem cell-derived cardiomyocytes on poly(lactic-co-glycolic acid) fiber sheets (3D-hiPSC-CTs) and cultured in the RWV bioreactor (RWV group) or under static conditions (control group). The tissues were transplanted into a myocardial infarction nude rat model, and cardiac performance was evaluated. In the RWV group, cell viability and contractile and electrical properties significantly improved, mature cardiomyocytes were observed, and mechanical stress-related mediators of mammalian target of rapamycin signaling were upregulated compared with those of the control. Four weeks post-transplantation, tissue survival and left ventricular ejection fraction significantly improved in the RWV group. Hence, dynamic culture in an RWV bioreactor could provide a superior culture environment for improved performance of 3D-hiPSC-CTs, providing a means for functional cardiomyogenesis in myocyte-loss heart failure.

Evaluation of cardiac allograft vasculopathy by positron emission tomography

Cardiac allograft vasculopathy (CAV) remains one of the most important late occurring complications in heart transplant (HT) recipients significantly effecting graft survival. Recently, there has been tremendous focus on the development of effective and safe non-invasive diagnostic strategies for the diagnosis of CAV employing a wide range of imaging technologies. During the past decade multiple studies have been published using positron emission tomography (PET) myocardial perfusion imaging, establishing the value of PET myocardial blood flow quantification for the evaluation of CAV. These independent investigations demonstrate that PET can be successfully used to establish the diagnosis of CAV, can be utilized for prognostication and may be used for serial monitoring of HT recipients. In addition, molecular imaging techniques have started to emerge as new tools to enhance our knowledge to better understand the pathophysiology of CAV.

Non-HLA antibodies targeting angiotensin II type 1 receptors and endothelin-1 type A receptors impair endothelial repair via a β2-arrestin link to the mTOR pathway

Functional non-HLA antibodies (antibodies to non-human leukocyte antigens) targeting the G protein-coupled receptors angiotensin II type 1 receptor (AT1R) and endothelin-1 type A receptor (ETAR) are implicated in the pathogenesis of transplant vasculopathy. While ERK signaling (a regulator of cell growth) may represent a general cellular response to agonist stimulation, the molecular link between receptor stimulation and development of vascular obliteration has not been fully established. Here we hypothesize involvement of the versatile adaptor proteins, β-arrestins, and the major regulator of cell growth, PI3K/mTOR signaling, in impaired endothelial repair. To test this, human microvascular endothelial cells were treated with AT1R/ETAR antibodies isolated from patients with kidney transplant vasculopathy. These antibodies activated both mTOR complexes via AT1R and ETAR in a PI3K-dependent and ERK-independent manner. The mTOR inhibitor, rapamycin, completely abolished activation of mTORC1 and mTORC2 after long-term treatment with receptor antibodies. Imaging studies revealed that β2- but not β1-arrestin was recruited to ETAR in response to ET1 and patient antibodies but not with antibodies isolated from healthy individuals. Silencing of β2-arrestin by siRNA transfection significantly reduced ERK1/2 and mTORC2 activation. Non-HLA antibodies impaired endothelial repair by AT1R- and ETAR-induced mTORC2 signaling. Thus, we provide evidence that functional AT1R/ETAR antibodies induce ERK1/2 and mTOR signaling involving β2-arrestin in human microvascular endothelium. Hence, our data may provide a translational rational for mTOR inhibitors in combination with receptor blockers in patients with non-HLA receptor recognizing antibodies.

Diagnosis and management of cardiac allograft vasculopathy

One of the main causes of death beyond the first year after heart transplantation is cardiac allograft vasculopathy (CAV). This review summarises the current understanding of its complex pathophysiology, detection and treatment, including the available data on non-invasive imaging modalities used for screening and diagnosis. A better understanding of this entity is crucial to improving the long-term outcomes of the growing population of patients with a heart transplant.

Phosphorylated S6 ribosomal protein expression by immunohistochemistry correlates with de novo donor-specific HLA antibodies in lung allograft recipients

BACKGROUND

Per the ISHLT 2016 definition, a C4d-positive lung biopsy is required to meet criteria for definite antibody-mediated rejection (AMR). Unfortunately, C4d has poor sensitivity and specificity, and low inter-rater reliability. Phosphorylated S6 ribosomal protein (p-S6RP) expressed via the mTOR pathway has been shown to be a biomarker of AMR and correlates with donor-specific antibodies (DSA) in heart allografts. However, p-S6RP immunohistochemistry (IHC) in the setting of pulmonary AMR has yet to be evaluated. We sought to determine whether p-S6RP IHC performed on lung biopsies correlates with de novo DSA.

METHODS

IHC for p-S6RP performed on 26 biopsies from lung transplant recipients with de novo HLA DSA (DSA+) and 28 biopsies from patients with no DSA (DSA-) were evaluated by 3 pathologists who independently scored the degree of alveolar macrophage and pneumocyte staining. Staining in ≥50% of the biopsy as determined by at least 2 pathologists was considered positive.

RESULTS

Twenty-one (81%) DSA+ biopsies stained positive for p-S6RP in pneumocytes and 21 (81%) in macrophages. Six DSA- biopsies (21%) stained positive for p-S6RP in pneumocytes, 6 (21%) were positive in macrophages. Pneumocyte p-S6RP staining was 81% sensitive and 79% specific for DSA. Macrophage staining showed the same sensitivity and specificity but with lower inter-rater agreement (κ = 0.53 vs 0.68).

CONCLUSIONS

This study demonstrates a positive relationship between de novo DSA and p-S6RP expression in pneumocytes and macrophages using IHC. p-S6RP is relatively sensitive and specific, and has superior inter-rater reliability compared to C4d.

Knockdown of lncRNA MIR4435‑2HG and ST8SIA1 expression inhibits the proliferation, invasion and migration of prostate cancer cells in vitro and in vivo by blocking the activation of the FAK/AKT/β‑catenin signaling pathway

Prostate cancer is a main health risk for males with a high incidence and mortality. The present study aimed to examine the effects of long non‑coding RNA (lncRNA) MIR4435‑2HG binding with ST8SIA1 on the proliferation, invasion and migration of prostate cancer cells via the activation of the FAK/AKT/β‑catenin signaling pathway. The expression of MIR4435‑2HG and ST8SIA1 in prostate cancer cell lines, and the transfection efficacy were analyzed by RT‑qPCR. The proliferation, clone formation ability, and the invasion and migration of transfected cells were detected by CCK‑8 assay, clone formation assay, Transwell assay and wound healing assay, respectively. Plasmids were injected subcutaneously into mice to construct a xenograft tumor model. The expression levels of proteins related to proliferation, apoptosis, invasion and migration, and the FAK/AKT/β‑catenin pathway were detected by western blot analysis. The results revealed that MIR4435‑2HG expression was increased in the prostate cancer cell lines and MIR4435‑2HG expression was the highest in the PC‑3 cells. Interference with MIR4435‑2HG inhibited the proliferation, clone formation ability, and the invasion and migration of PC‑3 cells, as well as tumor growth by suppressing the activation of the FAK/AKT/β‑catenin signaling pathway. MIR4435‑2HG was demonstrated to target ST8SIA1. ST8SIA1 expression was also increased in the prostate cancer cell lines and MIR4435‑2HG expression was the highest in the PC‑3 cells. Interference with ST8SIA1 inhibited the promoting effects of MIR4435‑2HG on the proliferation, invasion and migration of PC‑3 cells, as well as tumor growth by suppressing the activation of the FAK/AKT/β‑catenin signaling pathway. On the whole, the present study demonstrates that interference with MIR4435‑2HG, combined with ST8SIA1, inhibits the proliferation, invasion and migration of prostate cancer cells in vitro and in vivo by blocking the activation of the FAK/AKT/β‑catenin signaling pathway.

Comparative analysis of complement-dependent lymphocytotoxicity crossmatch and flow cytometry crossmatch results versus Luminex single-antigen bead-based donor-specific IgG class I antibody MFI values in live related renal transplant cases; a retrospective observation in 102 cases

The aim of this study was to compare the results of solid phase assay and cell-based assay, and explore the near-accurate DSA-MFI-cutoff value detected on solid phase assay above which the cell-based assay would show a positive result. In this retrospective study, 102 prospective renal transplant recipients were tested for the presence of donor-specific antibodies (DSAs) by cell-based assay (T-cell-CDC-AHG-XM and T-cell-IgG-FC-XM) and solid phase assay (class-I-IgG-L-SAB) with their corresponding donor. Among the 40 patients in the group first (L-SAB-DSA-MFI<1000), one case was positive in IgG-T-cell-FC-XM while T-cell-CDC-AHG-XM was negative in all the cases. In the second group having L-SAB-DSA-MFI values between 1000 and 3000, 19 cases were positive and the remaining 11 cases were negative in IgG-T-cell-FC-XM. T-cell-CDC-AHG-XM showed a negative reaction in all 30 cases. In the third group having L-SAB-DSA-MFI values between 3000 and 5000, IgG-T-cell-FC-XM was positive in 18 cases while, two were negative. T-cell-CDC-AHG-XM demonstrated a negative result in 14 cases while reaming six cases demonstrated a positive result. In the fourth group having L-SAB-DSA-MFI values >5000, all 12 cases showed a positive result in both IgG-T-cell FC-XM and T-cell-CDC-AHG-XM. Our results indicated that the L-SAB-DSA-MFI values >2215 were significantly (P < .001) correlated with positive IgG-T-cell-FC-XM while L-SAB-DSA-MFI values >4689 were significantly (P < .001) correlated with positive CDC-XM.

The effect of anti‑HLA class I antibodies on the immunological properties of human glomerular endothelial cells and their modification by mTOR inhibition or GCN2 kinase activation

In antibody‑mediated rejection (ABMR), the graft endothelium is at the forefront of the kidney transplant against the assault from the recipient's humoral immune system, and is a target of the latter. The present study investigated the effect of antibodies against human leukocyte antigen (HLA) class I (anti‑HLAI) on the immunological properties of human glomerular endothelial cells. Additionally, the effect of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) inhibitor (everolimus), or the general control nonderepressible 2 kinase (GCN2K) activator (halofuginone) on anti‑HLAI antibody‑mediated alterations was assessed. Cell integrity was examined, an lactate dehydrogenase (LDH) release assay was performed and cleaved caspase‑3 levels were determined. Furthermore, cell proliferation was analyzed by performing a bromodeoxyuridine assay and the cellular proteins involved in signal transduction or immune effector mechanisms were assessed via western blotting. IL‑8, monocyte chemoattractive protein‑1 (MCP‑1), von Willebrand factor (vWF) and transforming growth factor‑beta 1 (TGF‑β1) were assayed via ELISA. The results revealed that anti‑HLAI triggered integrin signaling, activated mTOR and GCN2K, preserved cell integrity and promoted cell proliferation. Additionally, by increasing intercellular adhesion molecule 1 (ICAM‑1), HLA‑DR, IL‑8 and MCP‑1 levels, anti‑HLAI enhanced the ability of immune cells to interact with endothelial cells thus facilitating graft rejection. Contrarily, by upregulating CD46 and CD59, anti‑HLAI rendered the endothelium less vulnerable to complement‑mediated injury. Finally, by enhancing vWF and TGF‑β1, anti‑HLAI may render the endothelium prothrombotic and facilitate fibrosis and graft failure, respectively. According to our results, mTORC1 inhibition and GCN2K activation may prove useful pharmaceutical targets, as they prevent cell proliferation and downregulate ICAM‑1, IL‑8, MCP‑1 and TGF‑β1. mTORC1 inhibition also decreases vWF.

Non-immune risk predictors of cardiac allograft vasculopathy: Results from the U.S. organ procurement and transplantation network

BACKGROUND

Cardiac allograft vasculopathy (CAV) remains a major long-term complication in heart transplant (HT) recipients related to increased mortality. We aimed to identify non-immune recipient- and donor-related risk factors for the development of CAV in HT patients.

METHODS

40,647 recipients, prospectively enrolled from April 1995 to January 2019 in the Organ Procurement and Transplantation Network (OPTN), were analyzed after exclusion of pediatric patients, those with missing information on CAV, and re-transplantation. Multivariable-adjusted Cox regression analyses were performed to identify recipient- and donor-related risk factors for CAV. 5-year population attributable risk for classical cardiovascular risk factors was calculated to estimate the recipients' CAV risk. Analyses were based on OPTN data (June 30, 2019).

RESULTS

Of 40,647 post-transplant patients, 14,698 (36.2%) developed CAV with a higher incidence in males (37.3%) than in females (32.6%) (p < 0.001). The mean follow-up time was 68.2 months. In recipients, male sex, African American and Asian ethnicity, ischemic cardiomyopathy, body mass index and smoking were associated with CAV occurrence. In donors, older age, male sex, smoking, diabetes and arterial hypertension were related to CAV. Results remained fairly stable after analysis of different time periods. 5-year attributable CAV risk for classical cardiovascular risk factors was 9.1%.

CONCLUSIONS

In this large registry with known limitations concerning data completeness, CAV incidence was higher in males than in females. Next to male sex and donor age, the classical cardiovascular risk factors were related to incident CAV. Classical cardiovascular risk factors played only a minor role for the 5-year attributable CAV risk.

Reverse Signaling by MHC-I Molecules in Immune and Non-Immune Cell Types

Major histocompatibility complex (MHC) molecules are well-known for their role in antigen (cross-) presentation, thereby functioning as key players in the communication between immune cells, for example dendritic cells (DCs) and T cells, or immune cells and their targets, such as T cells and virus-infected or tumor cells. However, much less appreciated is the fact that MHC molecules can also act as signaling receptors. In this process, here referred to as reverse MHC class I (MHC-I) signaling, ligation of MHC molecules can lead to signal-transduction and cell regulatory effects in the antigen presenting cell. In the case of MHC-I, reverse signaling can have several outcomes, including apoptosis, migration, induced or reduced proliferation and cytotoxicity towards target cells. Here, we provide an overview of studies showing the signaling pathways and cell outcomes upon MHC-I stimulation in various immune and non-immune cells. Signaling molecules like RAC-alpha serine/threonine-protein kinase (Akt1), extracellular signal-regulated kinases 1/2 (ERK1/2), and nuclear factor-κB (NF-κB) were common signaling molecules activated upon MHC-I ligation in multiple cell types. For endothelial and smooth muscle cells, the in vivo relevance of reverse MHC-I signaling has been established, namely in the context of adverse effects after tissue transplantation. For other cell types, the role of reverse MHC-I signaling is less clear, since aspects like the in vivo relevance, natural MHC-I ligands and the extended downstream pathways are not fully known.The existing evidence, however, suggests that reverse MHC-I signaling is involved in the regulation of the defense against bacterial and viral infections and against malignancies. Thereby, reverse MHC-I signaling is a potential target for therapies against viral and bacterial infections, cancer immunotherapies and management of organ transplantation outcomes.

Ligation of HLA Class I Molecules Induces YAP Activation through Src in Human Endothelial Cells

Ab cross-linking of HLA class I (HLA I) molecules on the surface of endothelial cells (EC) triggers proliferative and prosurvival intracellular signaling, which is implicated in the process of chronic allograft rejection, also known as transplant vasculopathy. Despite the importance of Ab-mediated rejection in transplantation, the mechanisms involved remain incompletely understood. In this study, we examined the regulation of yes-associated protein (YAP) localization, phosphorylation, and transcriptional activity in human ECs challenged with Abs that bind HLA I. In unstimulated ECs, YAP localized mainly in the cytoplasm. Stimulation of these cells with Ab W6/32 induced marked translocation of YAP to the nucleus. The nuclear import of YAP was associated with a rapid decrease in YAP phosphorylation at Ser127 and Ser397, sites targeted by LATS1/2 and with the expression of YAP-regulated genes, including connective tissue growth factor (CTGF), and cysteine-rich angiogenic inducer 61 (CYR61). Transfection of small interfering RNAs targeting YAP/TAZ blocked the migration of ECs stimulated by ligation of HLA I, indicating that YAP mediates the increase in EC migration induced by HLA I ligation. Treatment of intact ECs with Src family inhibitors induced cytoplasmic localization of YAP in unstimulated ECs and, strikingly, blocked the nuclear import of YAP induced by Ab-induced HLA I activation in these cells and the increase in the expression of the YAP-regulated genes CTGF and CYR61 induced by HLA I stimulation. Our results identify the Src/YAP axis as a key player in promoting the proliferation and migration of ECs that are critical in the pathogenesis of transplant vasculopathy.

Extracellular Matrix Injury of Kidney Allografts in Antibody-Mediated Rejection: A Proteomics Study

BACKGROUND

Antibody-mediated rejection (AMR) accounts for >50% of kidney allograft loss. Donor-specific antibodies (DSA) against HLA and non-HLA antigens in the glomeruli and the tubulointerstitium cause AMR while inflammatory cytokines such as TNFα trigger graft injury. The mechanisms governing cell-specific injury in AMR remain unclear.

METHODS

Unbiased proteomic analysis of laser-captured and microdissected glomeruli and tubulointerstitium was performed on 30 for-cause kidney biopsy specimens with early AMR, acute cellular rejection (ACR), or acute tubular necrosis (ATN).

RESULTS

A total of 107 of 2026 glomerular and 112 of 2399 tubulointerstitial proteins was significantly differentially expressed in AMR versus ACR; 112 of 2026 glomerular and 181 of 2399 tubulointerstitial proteins were significantly dysregulated in AMR versus ATN (P<0.05). Basement membrane and extracellular matrix (ECM) proteins were significantly decreased in both AMR compartments. Glomerular and tubulointerstitial laminin subunit γ-1 (LAMC1) expression decreased in AMR, as did glomerular nephrin (NPHS1) and receptor-type tyrosine-phosphatase O (PTPRO). The proteomic analysis revealed upregulated galectin-1, which is an immunomodulatory protein linked to the ECM, in AMR glomeruli. Anti-HLA class I antibodies significantly increased cathepsin-V (CTSV) expression and galectin-1 expression and secretion in human glomerular endothelial cells. CTSV had been predicted to cleave ECM proteins in the AMR glomeruli. Glutathione S-transferase ω-1, an ECM-modifying enzyme, was significantly increased in the AMR tubulointerstitium and in TNFα-treated proximal tubular epithelial cells.

CONCLUSIONS

Basement membranes are often remodeled in chronic AMR. Proteomic analysis performed on laser-captured and microdissected glomeruli and tubulointerstitium identified early ECM remodeling, which may represent a new therapeutic opportunity.

The role of optical coherence tomography and other intravascular imaging modalities in cardiac allograft vasculopathy

Orthotopic heart transplantation (OHT) is the standard-of-care for end-stage heart disease. Although a significant improvement in the prognosis of patients after OHT has been observed in recent years, their overall mortality remains relatively high, with a median survival of approximately 10 years after transplantation. One of the primary causes of death in patients after OHT is cardiac allograft vasculopathy (CAV), the condition developing specifically in the coronary vasculature after OHT, the pathophysiology of which is still inadequately known. It is estimated that CAV development and progression is responsible for approximately 30% of deaths within five years post-OHT. According to the International Society for Heart and Lung Transplantation (ISHLT) Nomenclature for CAV, its presence should be assessed primarily by the coronary angiography performed routinely after OHT, mostly due to its wide availability, reproducibility, and low complication rate. However, the analysis of CAV in coronary angiography has limitations, mostly concerning its - sometimes inadequate - sensitivity and specificity. Hence, there is a growing need for the introduction of more accurate methods of CAV assessment, such as intravascular imaging, which through a thorough evaluation of the arterial wall structure and thickness allows the drawbacks of routine angiography to be minimised. The aim of the article was to critically summarise the current findings derived from the analysis of CAV by optical coherence tomography, the other intravascular imaging modalities, such as intravascular ultrasound (IVUS) and IVUS-derived virtual histology, along with physiological assessment with the use of the fractional flow reserve.

Significance of Luminex-based single antigen class II bead assay and its mean fluorescence intensity in renal transplant cases; a retrospective observation in 97 cases

The objective of this study was to determine the mean fluorescence intensity (MFI) values of class II Luminex single antigen bead (L-SAB) assay and compare these MFI values with cell-based complement-dependent cytotoxicity crossmatch with anti-human globulin (CDC-AHG-XM) and IgG-B-cell flow cytometry crossmatch (FC-XM) results and explore the near-accurate MFI-cutoff values of positive cell-based crossmatch results. This retrospective study was an analysis in 97 renal transplant recipients, who were tested for the presence of DSA by CDC-AHG-XM and IgG-B-cell-FC-XM methods with their corresponding donor as well as for anti-human leukocyte antigen (HLA) antibody detection using a sensitive L-SAB assay. In the group having DSA MFI values <1000, none of the patients showed positivity for FC-XM and CDC-AHG-XM; in the group having MFI values between 1000 and 3000, 35.48% showed positivity for FC-XM but none by the CDC-AHG-XM method. However, in the group having MFI values >3000, 83.33% of cases were positive for FC-XM. Further, in those groups with MFI values between 3000 and 6000, 38.09% were positive for CDC-AHG-XM, while 86.66% showed positivity in the group with MFI >6000. Our results indicated that Luminex-DSA MFI value >1995 (P < .0001) significantly correlated with IgG-B-cell-FC-XM positivity while Luminex-DSA MFI value of >4247 (P < .0006) was significantly correlated with positive CDC-AHG-XM. MFI cutoff of 1995 exhibited a diagnostic sensitivity of 97.56% and specificity of 89.29% for predicting positive IgG B-cell FC-XM and MFI cutoff of 4247 exhibited a diagnostic sensitivity of 90.48% and specificity of 97.37% for predicting positive CDC-AHG-XM. However, a cutoff MFI of >5000 and >7000 for SAB assay had a sensitivity and specificity of 100% in detecting a positive IgG B-cell FC-XM and CDC-AHG-XM, respectively.

mTOR Inhibitor Therapy Diminishes Circulating CD8+ CD28- Effector Memory T Cells and Improves Allograft Inflammation in Belatacept-refractory Renal Allograft Rejection

BACKGROUND

Renal allograft rejection is more frequent under belatacept-based, compared with tacrolimus-based, immunosuppression. We studied kidney transplant recipients experiencing rejection under belatacept-based early corticosteroid withdrawal following T-cell-depleting induction in a recent randomized trial (Belatacept-based Early Steroid Withdrawal Trial, clinicaltrials.gov NCT01729494) to determine mechanisms of rejection and treatment.

METHODS

Peripheral mononuclear cells, serum creatinine levels, and renal biopsies were collected from 8 patients undergoing belatacept-refractory rejection (BRR). We used flow cytometry, histology, and immunofluorescence to characterize CD8 effector memory T cell (TEM) populations in the periphery and graft before and after mammalian target of rapamycin (mTOR) inhibition.

RESULTS

Here, we found that patients with BRR did not respond to standard antirejection therapy and had a substantial increase in alloreactive CD8 T cells with a CD28/DR/CD38/CD45RO TEM. These cells had increased activation of the mTOR pathway, as assessed by phosphorylated ribosomal protein S6 expression. Notably, everolimus (an mTOR inhibitor) treatment of patients with BRR halted the in vivo proliferation of TEM cells and their ex vivo alloreactivity and resulted in their significant reduction in the peripheral blood. The frequency of circulating FoxP3 regulatory T cells was not altered. Importantly, everolimus led to rapid resolution of rejection as confirmed by histology.

CONCLUSIONS

Thus, while prior work has shown that concomitant belatacept + mTOR inhibitor therapy is effective for maintenance immunosuppression, our preliminary data suggest that everolimus may provide an available means for effecting "rescue" therapy for rejections occurring under belatacept that are refractory to traditional antirejection therapy with corticosteroids and polyclonal antilymphocyte globulin.

Cardiac allograft vasculopathy: Insights on pathogenesis and therapy

Cardiac allograft vasculopathy (CAV) is a unique accelerated form of coronary vascular disease affecting heart transplant recipients. This complication is a significant contributor to medium- to long-term post-transplant morbidity and mortality. There is a high prevalence of CAV with approximately one in three patients developing CAV by 5 years post-transplant. Morphologically, CAV is characterized by concentric coronary intimal hyperplasia in both the epicardial arteries and intramural microvasculature. Although several immune and non-immune factors have been identified, their precise pathogenic mechanisms, interactions, and relative importance in the development of CAV are not well defined. The advent of improved imaging surveillance modalities has resulted in earlier detection during the disease process. However, overall management of CAV remains challenging due to paucity of treatment. This review aims to discuss key concepts on the pathogenesis of CAV and current management strategies, focusing on the use of mammalian target of rapamycin inhibitors.

Endothelium structure and function in kidney health and disease

The kidney harbours different types of endothelia, each with specific structural and functional characteristics. The glomerular endothelium, which is highly fenestrated and covered by a rich glycocalyx, participates in the sieving properties of the glomerular filtration barrier and in the maintenance of podocyte structure. The microvascular endothelium in peritubular capillaries, which is also fenestrated, transports reabsorbed components and participates in epithelial cell function. The endothelium of large and small vessels supports the renal vasculature. These renal endothelia are protected by regulators of thrombosis, inflammation and complement, but endothelial injury (for example, induced by toxins, antibodies, immune cells or inflammatory cytokines) or defects in factors that provide endothelial protection (for example, regulators of complement or angiogenesis) can lead to acute or chronic renal injury. Moreover, renal endothelial cells can transition towards a mesenchymal phenotype, favouring renal fibrosis and the development of chronic kidney disease. Thus, the renal endothelium is both a target and a driver of kidney and systemic cardiovascular complications. Emerging therapeutic strategies that target the renal endothelium may lead to improved outcomes for both rare and common renal diseases.

Molecular Patterns Discriminate Accommodation and Subclinical Antibody-mediated Rejection in Kidney Transplantation

BACKGROUND

Accommodation in ABO-incompatible (ABOi) transplantation and subclinical antibody-mediated rejection in HLA-incompatible (HLAi) transplantation share several morphological similarities. Because the clinical long-term outcomes differ, we hypothesized different molecular processes involved in ABOi transplantation and subclinical antibody-mediated rejection.

METHODS

Using Illumina Human HT-12 v4 Expression BeadChips, the whole transcriptome was evaluated based on 3-month protocol C4d+ biopsies in otherwise stable ABOi and HLAi kidney grafts, as well as in C4d-negative HLA-compatible grafts exhibiting normal histological findings. Top differently regulated genes were further validated using real-time quantitative polymerase chain reaction in another patient cohort and complement regulatory proteins by immunohistochemistry.

RESULTS

In the case of genes involved in immune response-related biological processes, ABOi and HLAi cohorts had similar transcriptomic profiles to C4d-negative controls. The majority of deregulated genes in the ABOi and HLAi groups consisted of metallothioneins and epithelial transporter genes. Increased expression of epithelial transporters (SLC4A1, SLC4A9, SLC17A3, SLC12A3, and SLC30A2) and class 1 metallothioneins (MT1F, MT1G, and MT1X) in HLAi transplantation was validated by real-time quantitative polymerase chain reaction. In comparison to controls, both incompatible cohorts were characterized by the upregulation of intrarenal complement regulatory genes. CD46 and CD59 transcripts were increased in the ABOi cohort, whereas CD46 solely in HLAi group, and CD59 protein expression was similar in both incompatible groups.

CONCLUSIONS

Several epithelial transporters and metallothioneins discriminate subclinical antibody-mediated rejection in HLAi transplantation from accommodation in ABOi transplantation, which suggest different involved downstream mechanisms and increased risk of injury in HLAi settings. Metallothioneins with their antioxidative properties may help to attenuate the inflammation response induced by donor-specific anti-HLA antibody binding.

Back signaling of HLA class I molecules and T/NK cell receptor ligands in epithelial cells reflects the rejection-specific microenvironment in renal allograft biopsies

The role of endothelial cells in the pathophysiology of antibody-mediated rejection after renal transplantation has been widely investigated. We expand this scenario to the impact of epithelial cells on the microenvironment during rejection. Primary proximal tubular epithelial cells were stimulated via HLA class I, CD155 and CD166 based on their potential signal-transducing capacity to mediate back signaling after encounter with either T/NK cells or donor-specific antibodies. Upon crosslinking of these ligands with mAbs, PTEC secreted IL-6, CXCL1,8,10, CCL2, and sICAM-1. These proteins were also released by PTEC as consequence of a direct interaction with T/NK cells. Downmodulation of the receptor CD226 on effector cells confirmed the involvement of this receptor/ligand pair in back signaling. In vivo, CD155 and CD166 expression was detectable in proximal and distal tubuli of renal transplant biopsies, respectively. The composition of the protein microenvironment in these biopsies showed a substantial overlap with the PTEC response. Cluster and principal component analyses of the microenvironment separated unsuspicious from rejection biopsies and, furthermore, ABMR, TCMR, and borderline rejection. In conclusion, our results provide evidence that epithelial cells may contribute to the rejection process and pave the way to a better understanding of the pathomechanisms of kidney allograft rejection.

The determinants, biomarkers, and consequences of microvascular injury in kidney transplant recipients

Independent of the initial cause of kidney disease, microvascular injury to the peritubular capillary network appears to play a central role in the development of interstitial fibrosis in both native and transplanted kidney disease. This association is explained by mechanisms such as the upregulation of profibrotic genes and epigenetic changes induced by hypoxia, capillary leakage, endothelial and pericyte transition to interstitial fibroblasts, as well as modifications in the secretome of endothelial cells. Alloimmune injury due to antibody-mediated rejection and ischemia-reperfusion injury are the two main etiologies of microvascular damage in kidney transplant recipients. The presence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies, histological findings, such as diffuse C4d staining in peritubular capillaries, and the extent and severity of peritubular capillaritis, are commonly used clinically to provide both diagnostic and prognostic information. Complement-dependent assays, circulating non-HLA antibodies, or evaluation of the microvasculature with novel imaging techniques are the subject of ongoing studies.

ST8SIA1 Regulates Tumor Growth and Metastasis in TNBC by Activating the FAK-AKT-mTOR Signaling Pathway

Breast cancer stem-like cells (BCSC) are implicated in cancer recurrence and metastasis of triple-negative breast cancer (TNBC). We have recently discovered that ganglioside GD2 expression defines BCSCs and that ST8SIA1 regulates GD2 expression and BCSC function. In this report, we show that ST8SIA1 is highly expressed in primary TNBC; its expression is positively correlated with the expression of several BCSC-associated genes such as BCL11A, FOXC1, CXCR4, PDGFRβ, SOX2, and mutations in p53. CRISPR knockout of ST8SIA1 completely inhibited BCSC functions, including in vitro tumorigenesis and mammosphere formation. Mechanistic studies discovered activation of the FAK-AKT-mTOR signaling pathway in GD2⁺ BCSCs, and its tight regulation by ST8SIA1. Finally, knockout of ST8SIA1 completely blocked in vivo tumor growth and metastasis by TNBC cells. In summary, these data demonstrate the mechanism by which ST8SIA1 regulates tumor growth and metastasis in TNBC and identifies it as a novel therapeutic target.

Single-Cell Transcriptomics of a Human Kidney Allograft Biopsy Specimen Defines a Diverse Inflammatory Response

Background Single-cell genomics techniques are revolutionizing our ability to characterize complex tissues. By contrast, the techniques used to analyze renal biopsy specimens have changed little over several decades. We tested the hypothesis that single-cell RNA-sequencing can comprehensively describe cell types and states in a human kidney biopsy specimen.Methods We generated 8746 single-cell transcriptomes from a healthy adult kidney and a single kidney transplant biopsy core by single-cell RNA-sequencing. Unsupervised clustering analysis of the biopsy specimen was performed to identify 16 distinct cell types, including all of the major immune cell types and most native kidney cell types, in this biopsy specimen, for which the histologic read was mixed rejection.Results Monocytes formed two subclusters representing a nonclassical CD16+ group and a classic CD16- group expressing dendritic cell maturation markers. The presence of both monocyte cell subtypes was validated by staining of independent transplant biopsy specimens. Comparison of healthy kidney epithelial transcriptomes with biopsy specimen counterparts identified novel segment-specific proinflammatory responses in rejection. Endothelial cells formed three distinct subclusters: resting cells and two activated endothelial cell groups. One activated endothelial cell group expressed Fc receptor pathway activation and Ig internalization genes, consistent with the pathologic diagnosis of antibody-mediated rejection. We mapped previously defined genes that associate with rejection outcomes to single cell types and generated a searchable online gene expression database.Conclusions We present the first step toward incorporation of single-cell transcriptomics into kidney biopsy specimen interpretation, describe a heterogeneous immune response in mixed rejection, and provide a searchable resource for the scientific community.

mTOR inhibitors and risk of chronic antibody-mediated rejection after kidney transplantation: where are we now?

Antibody-mediated rejection (AMR) usually starts with generation of donor-specific anti-HLA antibodies (DSAs), arising from a B-cell response to antigen recognition. In vitro and preclinical data demonstrate that mammalian target of rapamycin (mTOR) inhibition attenuates the mTOR-mediated intracellular signaling pathway involved in AMR-related kidney damage. The limited available data from immunological studies in kidney transplant patients, however, have not shown such effects in vivo. In terms of clinical immunosuppression, the overriding influence on rates of de novo DSA (dnDSA) or AMR-regardless of the type of regimen-is patient adherence. To date, limited data from patients given mTOR inhibitor therapy with adequate concurrent immunosuppression, such as reduced-exposure calcineurin inhibitor (CNI) therapy, have not shown an adverse effect on the risk of dnDSA or AMR. Early switch to an mTOR inhibitor (<6-12 months post-transplant) in a CNI-free regimen, in contrast, can increase the risk of dnDSA, especially if adjunctive therapy is inadequate. Late conversion to CNI-free therapy with mTOR inhibition does not appear to affect the risk of dnDSA. More data, from prospective studies, are required to fully understand that association between use of mTOR inhibitors with different types of concomitant therapy and risk of dnDSA and AMR.

Outside-in HLA class I signaling regulates ICAM-1 clustering and endothelial cell-monocyte interactions via mTOR in transplant antibody-mediated rejection

Antibody-mediated rejection (AMR) resulting in transplant allograft vasculopathy (TAV) is the major obstacle for long-term survival of solid organ transplants. AMR is caused by donor-specific antibodies to HLA, which contribute to TAV by initiating outside-in signaling transduction pathways that elicit monocyte recruitment to activated endothelium. Mechanistic target of rapamycin (mTOR) inhibitors can attenuate TAV; therefore, we sought to understand the mechanistic underpinnings of mTOR signaling in HLA class I Ab-mediated endothelial cell activation and monocyte recruitment. We used an in vitro model to assess monocyte binding to HLA I Ab-activated endothelial cells and found mTOR inhibition reduced ezrin/radixin/moesin (ERM) phosphorylation, intercellular adhesion molecule 1 (ICAM-1) clustering, and monocyte firm adhesion to HLA I Ab-activated endothelium. Further, in a mouse model of AMR, in which C57BL/6. RAG1^-/- recipients of BALB/c cardiac allografts were passively transferred with donor-specific MHC I antibodies, mTOR inhibition significantly reduced vascular injury, ERM phosphorylation, and macrophage infiltration of the allograft. Taken together, these studies indicate mTOR inhibition suppresses ERM phosphorylation in endothelial cells, which impedes ICAM-1 clustering in response to HLA class I Ab and prevents macrophage infiltration into cardiac allografts. These findings indicate a novel therapeutic application for mTOR inhibitors to disrupt endothelial cell-monocyte interactions during AMR.

HLA Class II-Triggered Signaling Cascades Cause Endothelial Cell Proliferation and Migration: Relevance to Antibody-Mediated Transplant Rejection

Transplant recipients developing donor-specific HLA class II (HLA-II) Abs are at higher risk for Ab-mediated rejection (AMR) and transplant vasculopathy. To understand how HLA-II Abs cause AMR and transplant vasculopathy, we determined the signaling events triggered in vascular endothelial cells (EC) following Ab ligation of HLA-II molecules. HLA-II expression in EC was induced by adenoviral vector expression of CIITA or by pretreatment with TNF-α/IFN-γ. Ab ligation of class II stimulated EC proliferation and migration. Class II Ab also induced activation of key signaling nodes Src, focal adhesion kinase, PI3K, and ERK that regulated downstream targets of the mammalian target of rapamycin (mTOR) pathway Akt, p70 ribosomal S6 kinase, and S6 ribosomal protein. Pharmacological inhibitors and small interfering RNA showed the protein kinases Src, focal adhesion kinase, PI3K/Akt, and MEK/ERK regulate class II Ab-stimulated cell proliferation and migration. Treatment with rapalogs for 2 h did not affect HLA-II Ab-induced phosphorylation of ERK; instead, mTOR complex (mTORC)1 targets were dependent on activation of ERK. Importantly, suppression of mTORC2 for 24 h with rapamycin or everolimus or treatment with mTOR active-site inhibitors enhanced HLA-II Ab-stimulated phosphorylation of ERK. Furthermore, knockdown of Rictor with small interfering RNA caused overactivation of ERK while abolishing phosphorylation of Akt Ser⁴⁷³ induced by class II Ab. These data are different from HLA class I Ab-induced activation of ERK, which is mTORC2-dependent. Our results identify a complex signaling network triggered by HLA-II Ab in EC and indicate that combined ERK and mTORC2 inhibitors may be required to achieve optimal efficacy in controlling HLA-II Ab-mediated AMR.

Pre-transplant Screening for Non-HLA Antibodies: Who should be Tested?

Retrospective studies of angiotensin II type 1 receptor antibodies (AT1R-Ab) and anti-endothelial cell antibodies (AECA) have linked these antibodies to allograft injury. Because rising healthcare costs dictate judicious use of laboratory testing, we sought to define characteristics of kidney transplant recipients who may benefit from screening for non-HLA antibodies. Kidney recipients transplanted between 2011 and 2016 at Johns Hopkins, were evaluated for AT1R-Ab and AECA. Pre-transplant antibody levels were compared to clinical and biopsy indications of graft dysfunction. Biopsies were graded using the Banff' 2009-2013 criteria. AT1R-Ab and AECA were detected using ELISA and endothelial cell crossmatches, respectively. AT1R-Ab levels were higher in patients who were positive for AECAs. Re-transplanted patients (p < 0.0001), males (p = 0.008) and those with FSGS (p = 0.04) and younger (p = 0.04) at time of transplantation were more likely to be positive for AT1R-Ab prior to transplantation. Recipients who were positive for AT1R-Ab prior to transplantation had increases in serum creatinine within 3 months post-transplantation (p < 0.0001) and developed abnormal biopsies earlier than did AT1R-Ab negative patients (126 days versus 368 days respectively; p = 0.02). Defining a clinical protocol to identify and preemptively treat patients at risk for acute rejection with detectable non-HLA antibodies is an important objective for the transplant community.

De Novo Donor-Specific Antibody Formation in Tacrolimus-Based, Mycophenolate Versus Mammalian Target of Rapamycin Immunosuppressive Regimens

OBJECTIVES

De novo donor-specific antibody formation posttransplant is associated with decreased graft survival. It is not known whether mammalian target of rapamycin inhibitors may be advantageous or detrimental compared with mycophenolate in the prevention of de novo donor-specific antibody formation.

MATERIALS AND METHODS

We compared 66 kidney and kidney-pancreas transplant recipients who received tacrolimus, mammalian target of rapamycin inhibitor, and prednisone (group 1; 36 of whom received everolimus and 30 of whom received sirolimus) versus 132 patients who received tacrolimus, mycophenolate, and prednisone (group 2) matched for age, sex, race, and type/timing of transplant from 2007 to 2012.

RESULTS

Rates of de novo donor-specific antibody formation were comparable between groups at 1, 6, and 12 months (16.7%, 25.8%, and 28.8% for group 1 vs 9.8%, 15.2%, and 22.0% for group 2). There were no significant differences in class (I, II, or mixed), strength (mean fluorescence intensity) of de novo donor-specific antibody, glomerular filtration rate, proteinuria levels, or acute rejection between the groups. In those with de novo donor-specific antibody by 6 months, acute rejection was more common versus those without de novo donor-specific antibody formation (24.3% vs 5.6% at 6 mo; P = .002), with rates of 27.0% versus 6.8% at 1 year (P = .001) and 40.7% versus 11.3% at 2 years (P < .001). An associated reduction in glomerular filtration rate also occurred.

CONCLUSIONS

Mammalian target of rapamycin inhibitors were neither protective nor permissive for de novo donor-specific antibody formation versus mycophenolate when used with clinically relevant tacrolimus dosing regimens.

The management of antibodies in heart transplantation: An ISHLT consensus document

Despite the successes from refined peri-operative management techniques and immunosuppressive therapies, antibodies remain a serious cause of morbidity and mortality for patients both before and after heart transplantation. Patients awaiting transplant who possess antibodies against human leukocyte antigen are disadvantaged by having to wait longer to receive an organ from a suitably matched donor. The number of pre-sensitized patients has been increasing, a trend that is likely due to the increased use of mechanical circulatory support devices. Even patients who are not pre-sensitized can go on to produce donor-specific antibodies after transplant, which are associated with worse outcomes. The difficulty in managing antibodies is uncertainty over which antibodies are of clinical relevance, which patients to treat, and which treatments are most effective and safe. There is a distinct lack of data from prospective trials. An international consensus conference was organized and attended by 103 participants from 75 centers to debate contentious issues, determine the best practices, and formulate ideas for future research on antibodies. Prominent experts presented state-of-the-art talks on antibodies, which were followed by group discussions, and then, finally, a reconvened session to establish consensus where possible. Herein we address the discussion, consensus points, and research ideas.

Endothelial chimerism and vascular sequestration protect pancreatic islet grafts from antibody-mediated rejection

Humoral rejection is the most common cause of solid organ transplant failure. Here, we evaluated a cohort of 49 patients who were successfully grafted with allogenic islets and determined that the appearance of donor-specific anti-HLA antibodies (DSAs) did not accelerate the rate of islet graft attrition, suggesting resistance to humoral rejection. Murine DSAs bound to allogeneic targets expressed by islet cells and induced their destruction in vitro; however, passive transfer of the same DSAs did not affect islet graft survival in murine models. Live imaging revealed that DSAs were sequestrated in the circulation of the recipients and failed to reach the endocrine cells of grafted islets. We used murine heart transplantation models to confirm that endothelial cells were the only accessible targets for DSAs, which induced the development of typical microvascular lesions in allogeneic transplants. In contrast, the vasculature of DSA-exposed allogeneic islet grafts was devoid of lesions because sprouting of recipient capillaries reestablished blood flow in grafted islets. Thus, we conclude that endothelial chimerism combined with vascular sequestration of DSAs protects islet grafts from humoral rejection. The reduced immunoglobulin concentrations in the interstitial tissue, confirmed in patients, may have important implications for biotherapies such as vaccines and monoclonal antibodies.

Complement-Mediated Enhancement of Monocyte Adhesion to Endothelial Cells by HLA Antibodies, and Blockade by a Specific Inhibitor of the Classical Complement Cascade, TNT003

Background

Antibody-mediated rejection (AMR) of most solid organs is characterized by evidence of complement activation and/or intragraft macrophages (C4d + and CD68+ biopsies). We previously demonstrated that crosslinking of HLA I by antibodies triggered endothelial activation and monocyte adhesion. We hypothesized that activation of the classical complement pathway at the endothelial cell surface by HLA antibodies would enhance monocyte adhesion through soluble split product generation, in parallel with direct endothelial activation downstream of HLA signaling.

Methods

Primary human aortic endothelial cells (HAEC) were stimulated with HLA class I antibodies in the presence of intact human serum complement. C3a and C5a generation, endothelial P-selectin expression, and adhesion of human primary and immortalized monocytes (Mono Mac 6) were measured. Alternatively, HAEC or monocytes were directly stimulated with purified C3a or C5a. Classical complement activation was inhibited by pretreatment of complement with an anti-C1s antibody (TNT003).

Results

Treatment of HAEC with HLA antibody and human complement increased the formation of C3a and C5a. Monocyte recruitment by human HLA antibodies was enhanced in the presence of intact human serum complement or purified C3a or C5a. Specific inhibition of the classical complement pathway using TNT003 or C1q-depleted serum significantly reduced adhesion of monocytes in the presence of human complement.

Conclusions

Despite persistent endothelial viability in the presence of HLA antibodies and complement, upstream complement anaphylatoxin production exacerbates endothelial exocytosis and leukocyte recruitment. Upstream inhibition of classical complement may be therapeutic to dampen mononuclear cell recruitment and endothelial activation characteristic of microvascular inflammation during AMR.

Valenzuela et al show that HLA antibody binding to human endothelial cells in vitro, triggered complement C3a and C5a deposition that mediated monocyte recruitment, and the salutary effects of inhibiting the classical complement pathway with an anti-C1s antibody. Supplemental digital content is available in the text.

Antibody-mediated rejection across solid organ transplants: manifestations, mechanisms, and therapies

Solid organ transplantation is a curative therapy for hundreds of thousands of patients with end-stage organ failure. However, long-term outcomes have not improved, and nearly half of transplant recipients will lose their allografts by 10 years after transplant. One of the major challenges facing clinical transplantation is antibody-mediated rejection (AMR) caused by anti-donor HLA antibodies. AMR is highly associated with graft loss, but unfortunately there are few efficacious therapies to prevent and reverse AMR. This Review describes the clinical and histological manifestations of AMR, and discusses the immunopathological mechanisms contributing to antibody-mediated allograft injury as well as current and emerging therapies.