HLA-G dimer targets Granzyme B pathway to prolong human renal allograft survival

Induction Therapies Determine the Distribution of Perforin and Granzyme B Transcripts in Kidney Transplant Recipients

Peripheral blood mononuclear cells contain secretory granules with Perforin and Granzyme B for defense against pathogens. The objective of the present study was to compare the effects of immunosuppressive induction therapies on Perforin and Granzyme B transcripts in kidney transplant recipients. Transcripts were determined in 408 incident kidney transplant recipients eight days posttransplant using quantitative real-time PCR. Compared to 90 healthy subjects, the median Perforin transcripts were lower in kidney transplant recipients with blood-group ABO-incompatible donors (N = 52), compatible living donors (N = 130), and deceased donors (N = 226) (25.7%; IQR, 6.5% to 46.0%; 31.5%; IQR, 10.9% to 57.7%; and 35.6%; IQR, 20.6% to 60.2%; respectively; p = 0.015 by the Kruskal-Wallis test). Kidney transplant recipients who were treated with thymoglobulin (N = 64) had significantly lower Perforin as well as Granzyme B compared to all other induction therapies (N = 344) (each p < 0.001). Receiver operator characteristics analysis showed that both Perforin (area under curve, 0.919) and Granzyme B (area under curve, 0.915) indicated thyroglobulin-containing induction therapies. Regression analysis showed that both reduction in plasma creatinine and human leukocyte antigen mismatches were positively associated with elevated Perforin/Granzyme B transcript ratio posttransplant. We conclude clinical parameters and therapies affect Perforin and Granzyme B transcripts posttransplant.

Cell Surface B2m-Free Human Leukocyte Antigen (HLA) Monomers and Dimers: Are They Neo-HLA Class and Proto-HLA?

Cell surface HLA-I molecules (Face-1) consist of a polypeptide heavy chain (HC) with two groove domains (G domain) and one constant domain (C-domain) as well as a light chain, B2-microglobulin (B2m). However, HCs can also independently emerge unfolded on the cell surface without peptides as B2m-free HC monomers (Face-2), B2m-free HC homodimers (Face 3), and B2m-free HC heterodimers (Face-4). The transport of these HLA variants from ER to the cell surface was confirmed by antiviral antibiotics that arrest the release of newly synthesized proteins from the ER. Face-2 occurs at low levels on the normal cell surface of the lung, bronchi, epidermis, esophagus, breast, stomach, ilium, colorectum, gall bladder, urinary bladder, seminal vesicles ovarian epithelia, endometrium, thymus, spleen, and lymphocytes. They are upregulated on immune cells upon activation by proinflammatory cytokines, anti-CD3 antibodies, antibiotics (e.g., ionomycin), phytohemagglutinin, retinoic acid, and phorbol myristate acetate. Their density on the cell surface remains high as long as the cells remain in an activated state. After activation-induced upregulation, the Face-2 molecules undergo homo- and hetero-dimerization (Face-3 and Face-4). Alterations in the redox environment promote dimerization. Heterodimerization can occur among and between the alleles of different haplotypes. The glycosylation of these variants differ from that of Face-1, and they may occur with bound exogenous peptides. Spontaneous arthritis occurs in HLA-B27+ mice lacking B2m (HLA-B27+ B2m-/-) but not in HLA-B27+ B2m+/- mice. The mice with HLA-B27 in Face-2 spontaneous configuration develop symptoms such as changes in nails and joints, hair loss, and swelling in paws, leading to ankyloses. Anti-HC-specific mAbs delay disease development. Some HLA-I polyreactive mAbs (MEM series) used for immunostaining confirm the existence of B2m-free variants in several cancer cells. The upregulation of Face-2 in human cancers occurs concomitantly with the downregulation of intact HLAs (Face-1). The HLA monomeric and dimeric variants interact with inhibitory and activating ligands (e.g., KIR), growth factors, cytokines, and neurotransmitters. Similarities in the amino acid sequences of the HLA-I variants and HLA-II β-chain suggest that Face-2 could be the progenitor of both HLA classes. These findings may support the recognition of these variants as a neo-HLA class and proto-HLA.

Dimerization of Transmembrane Proteins in Cancer Immunotherapy

Transmembrane proteins (TMEMs) are integrated membrane proteins that span the entire lipid bilayer and are permanently anchored to it. TMEMs participate in various cellular processes. Some TMEMs usually exist and perform their physiological functions as dimers rather than monomers. TMEM dimerization is associated with various physiological functions, such as the regulation of enzyme activity, signal transduction, and cancer immunotherapy. In this review, we focus on the dimerization of transmembrane proteins in cancer immunotherapy. This review is divided into three parts. First, the structures and functions of several TMEMs related to tumor immunity are introduced. Second, the characteristics and functions of several typical TMEM dimerization processes are analyzed. Finally, the application of the regulation of TMEM dimerization in cancer immunotherapy is introduced.

IL-10-producing memory B regulatory cells as a novel target for HLA-G to prolong human kidney allograft survival

Despite the growing interest in the role of regulatory B cells (Bregs) in autoimmunity, their distinct role and function in kidney transplant outcomes remain elusive. Here, we retrospectively analyzed the proportion of Bregs, transitional Bregs (tBregs) and memory Bregs (mBregs) and their capacity to produce IL-10 in non-rejected (NR) versus rejected (RJ) kidney transplant recipients. In the NR group, we observed a significant increase in the proportion of mBregs (CD19⁺CD24^hiCD27⁺) but no difference in tBregs (CD19⁺CD24^hiCD38⁺), as compared to the RJ group. We also observed a significant increase in IL-10-producing mBregs (CD19⁺CD24^hiCD27⁺IL-10⁺) in the NR group. As our group and others have previously reported a potential role of the human leukocyte antigen G (HLA-G) in human renal allograft survival, notably through IL-10, we then investigated possible crosstalk between HLA-G and IL-10⁺ mBregs. Our ex vivo data suggest a role of HLA-G in enhancing IL-10⁺ mBreg expansion upon stimulation, which further decreased CD3⁺ T cell proliferation capability. Using RNA-sequencing (RNA-seq), we identified potential key signaling pathways involved in HLA-G-driven IL-10⁺ mBreg expansion, such as the MAPK, TNF and chemokine signaling pathways. Together, our study highlights a novel HLA-G-mediated IL-10-producing mBreg pathway that may serve as a therapeutic target to improve kidney allograft survival.

HLA-G in asthma and its potential as an effective therapeutic agent

OBJECTIVE

Asthma is a heterogeneous disease. Severity of asthma and sensitivity to medications vary across asthma subtypes. Human leukocyte antigen (HLA)-G has a wide range of functions in normal and pathological physiology. Due to its powerful immune function, HLA-G participates in the pathogenesis of different asthma phenotypes by regulating the activity and function of various immune cells. The mechanism of HLA-G in asthma is not fully clear, and there is no consensus on its mechanism in asthma. Further studies are needed to explore the role of HLA-G in different phenotypes of human asthma.

METHODS

Observational study.

RESULTS

HLA-G is an important immunomodulatory factor in asthma. Studies have found different levels of HLA-G in patients with different asthma subtypes and healthy controls, but other studies have come to the opposite conclusion.

CONCLUSION

We speculate that further study on the mechanism of HLA-G in asthma pheno-types may explain some of the contradictions in current studies. Findings should provide information regarding the potential of HLA-G as a novel target for asthma diagnosis and treatment.

Involvement of circulating soluble HLA-G after liver transplantation in the low immunogenicity of hepatic allograft

Graft rejection is a critical risk in solid-organ transplantation. To decrease such risk, an understanding of the factors involved in low immunogenicity of liver allografts could potentially make it possible to transfer this tolerogenic property to other transplanted organs. HLA-G, a natural physiological molecule belonging to the Human Leukocyte Antigen class (HLA) Ib family that induces tolerance, is associated with fewer rejections in solid-organ transplantation. In contrast to HLA-G, HLA antigen incompatibilities between donor and recipient can lead to rejection, except in liver transplantation. We compared HLA-G plasma levels and the presence of anti-HLA antibodies before and after LT to understand the low immunogenicity of the liver. We conducted a large prospective study that included 118 patients on HLA-G plasma levels during a 12-month follow-up and compared them to the status of anti-HLA antibodies. HLA-G plasma levels were evaluated by ELISA at seven defined pre- and post-LT time points. HLA-G plasma levels were stable over time pre-LT and were not associated with patient characteristics. The level increased until the third month post-LT, before decreasing to a level comparable to that of the pre-LT period at one year of follow-up. Such evolution was independent of biological markers and immunosuppressive treatment, except with glucocorticoids. An HLA-G plasma level ≤ 50 ng/ml on day 8 after LT was significantly associated with a higher rejection risk. We also observed a higher percentage of rejection in the presence of donor specific anti-HLA antibodies (DSA) and an association between the increase in HLA-G plasma levels at three months and the absence of DSA. The low immunogenicity of liver allografts could be related to early elevated levels of HLA-G, which lead, in turn, to a decrease in anti-HLA antibodies, opening potential new therapeutic strategies using synthetic HLA-G proteins.

Biological Characteristics of HLA-G and Its Role in Solid Organ Transplantation

Organ transplantation is a lifesaving option for patients with advanced diseases. Rejection is regarded as one of the most severe risk factors post-transplantation. A molecule that contributes to immune tolerance and resisting rejection is human leukocyte antigen (HLA)-G, which belongs to the non-classical major histocompatibility complex class (MHC) I family. HLA-G was originally found to play a role during pregnancy to maintain immune tolerance between mother and child. It is expressed in the placenta and detected in several body fluids as soluble factor as well as different membrane isoforms on cells. Recent findings on HLA-G show that it can also play multifaceted roles during transplantation. This review will explain the general characteristics and biological function of HLA-G and summarize the views supporting the tolerogenic and other roles of HLA-G to better understand its role in solid organ transplantation (SOT) and its complications. Finally, we will discuss potential future research on the role of HLA-G in prevention, diagnosis, and treatment in SOT.

HLA-G 14bp Ins/Del Polymorphism, Plasma Level of Soluble HLA-G, and Association with IL-6/IL-10 Ratio and Survival of Glioma Patients

HLA-G is an immune checkpoint molecule with immunosuppressive and anti-inflammatory activities, and its expression and level of its soluble form (sHLA-G) may play an important role in tumor prognosis. The HLA-G 14bp ins/del polymorphism and the plasma level of soluble HLA-G (sHLA-G) were investigated by a polymerase chain reaction and ELISA, respectively, in 59 glioma patients. A significantly higher proportion of glioma patients had the 14 nt insert in both homozygous and heterozygous states compared to the control group. Glioma patients also had higher plasma levels of sHLA-G. Patients with methylated MGMT promoters had lower levels of sHLA-G than those with unmethylated MGMT promoters. The level of sHLA-G negatively correlated with the overall survival of patients. Glioblastoma patients who survived more than one year after diagnosis had lower levels of sHLA-G than those surviving less than one year. Patients with sHLA-G levels below the cut-off value of 40 U/mL survived significantly longer than patients with sHLA-G levels above 40 U/mL. The levels of sHLA-G were also negatively correlated with the level of IL-6 (p = 0.0004) and positively with IL-10/IL-6 (p = 0.046). Conclusion: The presence of the 14 nt insert in both homozygous and heterozygous states of the HLA-G 14bp ins/del polymorphism is more frequent in glioma patients and the elevated plasma levels of sHLA-G are negatively associated with their survival.

The Human Leukocyte Antigen G as an Immune Escape Mechanism and Novel Therapeutic Target in Urological Tumors

The non-classical human leukocyte antigen G (HLA-G) is a potent regulatory protein involved in the induction of immunological tolerance. This is based on the binding of membrane-bound as well as soluble HLA-G to inhibitory receptors expressed on various immune effector cells, in particular NK cells and T cells, leading to their attenuated functions. Despite its restricted expression on immune-privileged tissues under physiological conditions, HLA-G expression has been frequently detected in solid and hematopoietic malignancies including urological cancers, such as renal cell and urothelial bladder carcinoma and has been associated with progression of urological cancers and poor outcome of patients: HLA-G expression protects tumor cells from anti-tumor immunity upon interaction with its inhibitory receptors by modulating both the phenotype and function of immune cells leading to immune evasion. This review will discuss the expression, regulation, functional and clinical relevance of HLA-G expression in urological tumors as well as its use as a putative biomarker and/or potential therapeutic target for the treatment of renal cell carcinoma as well as urothelial bladder cancer.

Placental Immune Tolerance and Organ Transplantation: Underlying Interconnections and Clinical Implications

The immune system recognizes and attacks non-self antigens, making up the cornerstone of immunity activity against infection. However, during organ transplantation, the immune system also attacks transplanted organs and leads to immune rejection and transplantation failure. Interestingly, although the embryo and placenta are semi-allografts, like transplanted organs, they can induce maternal tolerance and be free of a vigorous immune response. Also, embryo or placenta-related antibodies might adversely affect subsequent organ transplantation despite the immune tolerance during pregnancy. Therefore, the balance between the immune tolerance in maternal-fetal interface and normal infection defense provides a possible desensitization and tolerance strategy to improve transplantation outcomes. A few studies on mechanisms and clinical applications have been performed to explore the relationship between maternal-fetal immune tolerance and organ transplantation. However, up to now, the mechanisms underlying maternal-fetal immune tolerance remain vague. In this review, we provide an overview on the current understanding of immune tolerance mechanisms underlying the maternal-fetal interface, summarize the interconnection between immune tolerance and organ transplantation, and describe the adverse effect of pregnancy alloimmunization on organ transplantation.

HLA Class I Molecules as Immune Checkpoints for NK Cell Alloreactivity and Anti-Viral Immunity in Kidney Transplantation

Natural killer (NK) cells are innate lymphocytes that can kill diseased- or virally-infected cells, mediate antibody dependent cytotoxicity and produce type I immune-associated cytokines upon activation. NK cells also contribute to the allo-immune response upon kidney transplantation either by promoting allograft rejection through lysis of cells of the transplanted organ or by promoting alloreactive T cells. In addition, they protect against viral infections upon transplantation which may be especially relevant in patients receiving high dose immune suppression. NK cell activation is tightly regulated through the integrated balance of signaling via inhibitory- and activating receptors. HLA class I molecules are critical regulators of NK cell activation through the interaction with inhibitory- as well as activating NK cell receptors, hence, HLA molecules act as critical immune checkpoints for NK cells. In the current review, we evaluate how NK cell alloreactivity and anti-viral immunity are regulated by NK cell receptors belonging to the KIR family and interacting with classical HLA class I molecules, or by NKG2A/C and LILRB1/KIR2DL4 engaging non-classical HLA-E or -G. In addition, we provide an overview of the methods to determine genetic variation in these receptors and their HLA ligands.

Humanized Mouse Model as a Novel Approach in the Assessment of Human Allogeneic Responses in Organ Transplantation

The outcome of organ transplantation is largely dictated by selection of a well-matched donor, which results in less chance of graft rejection. An allogeneic immune response is the main immunological barrier for successful organ transplantation. Donor and recipient human leukocyte antigen (HLA) mismatching diminishes outcomes after solid organ transplantation. The current evaluation of HLA incompatibility does not provide information on the immunogenicity of individual HLA mismatches and impact of non-HLA-related alloantigens, especially in vivo. Here we demonstrate a new method for analysis of alloimmune responsiveness between donor and recipient in vivo by introducing a humanized mouse model. Using molecular, cellular, and genomic analyses, we demonstrated that a recipient's personalized humanized mouse provided the most sensitive assessment of allogeneic responsiveness to potential donors. In our study, HLA typing provided a better recipient-donor match for one donor among two related donors. In contrast, assessment of an allogeneic response by mixed lymphocyte reaction (MLR) was indistinguishable between these donors. We determined that, in the recipient's humanized mouse model, the donor selected by HLA typing induced the strongest allogeneic response with markedly increased allograft rejection markers, including activated cytotoxic Granzyme B-expressing CD8+ T cells. Moreover, the same donor induced stronger upregulation of genes involved in the allograft rejection pathway as determined by transcriptome analysis of isolated human CD45+cells. Thus, the humanized mouse model determined the lowest degree of recipient-donor alloimmune response, allowing for better selection of donor and minimized immunological risk of allograft rejection in organ transplantation. In addition, this approach could be used to evaluate the level of alloresponse in allogeneic cell-based therapies that include cell products derived from pluripotent embryonic stem cells or adult stem cells, both undifferentiated and differentiated, all of which will produce allogeneic immune responses.

Human leukocyte antigen-G upregulates immunoglobulin-like transcripts and corrects dysfunction of immune cells in immune thrombocytopenia

Human leukocyte antigen-G (HLA-G) is a non-classical major histocompatibility complex class I antigen with potent immune-inhibitory function. HLA-G benefit patients in allotransplantation and autoimmune diseases by interacting with its receptors, immunoglobulinlike transcripts. Here we observed significantly less HLA-G in plasma from immune thrombocytopenia (ITP) patients positive for anti-platelet autoantibodies compared with autoantibodies-negative patients or healthy controls, while we found that HLA-G is positively correlated with platelet counts in both patients and healthy controls. We also found less membranebound HLA-G and immunoglobulin-like transcripts on CD4⁺ and CD14⁺ cells in patients. Recombinant HLA-G upregulated immunoglobulin-like transcript 2 expression on CD4⁺ and immunoglobulin-like transcript 4 on CD14⁺ cells. HLA-G upregulated IL-4 and IL-10, and downregulated tumor necrosis factor-a, IL-12 and IL-17 secreted by patient peripheral blood mononuclear cells, suggesting a stimulation of Th2 differentiation and downregulation of Th1 and Th17 immune response. HLA-G-modulated dendritic cells from ITP patients showed decreased expression of CD80 and CD86, and suppressed CD4⁺ T-cell proliferation compared to unmodulated cells. Moreover, HLA-G-modulated cells from patients induced less platelet apoptosis. HLA-G administration also significantly alleviated thrombocytopenia in a murine model of ITP. In conclusion, our data demonstrated that impaired expression of HLA-G and immunoglobulin-like transcripts is involved in the pathogenesis of ITP; recombinant HLA-G can correct this abnormality via upregulation of immunoglobulin-like transcripts, indicating that HLA-G can be a diagnostic marker and a therapeutic option for ITP.

Immune Responses in Malaria and Vaccine Strategies

Malaria is a pandemic with nearly half of global population at risk, caused by parasite Plasmodium species, particularly P. falciparum with a high morbidity and mortality, especially among children. There is an urgent need for development of population protective vaccines, such as in sub-Saharan low-income countries, where P. falciparum malaria is endemic. After years of endeavour with children and adults for safety and efficacy clinical trials, the P. falciparum circumsporozoite protein antigen, is targeted by specific antibodies induced by recombinant vaccine, called TRS,S. TRS,S has been authorized by WHO and Malawi Government to be the first malaria vaccine for up to 2 years of aged children for protection against malaria. Other malaria vaccines in clinical trials are also very promising candidates, including the original live, X-ray attenuated P-sporozoite vaccine, inducing antigen-specific T cell immunity at liver stage. Malaria parasite at blood symptomatic stage is targeted by specific antibodies to parasite-infected erythrocytes, which are important against pathogenic placenta-infected erythrocyte sequestration. Here, the demographic distribution of Plasmodium species and their pathogenicity in infected people are discussed. The role of innate phagocytic cells and malaria antigen specific T cell immunity, as well as that of specific antibody production by B cells are highlighted. The paramount role of cytotoxic CD8⁺ T cellular immunity in malaria people protection is also included.

Got your mother in a whirl: The role of maternal T cells and myeloid cells in pregnancy

Appropriate development of the placenta is required for healthy pregnancy to occur. After implantation of the fertilized blastocyst, fetal trophoblasts invade the endometrium and myometrium of the mother's uterus to establish placentation. In this process, fetal trophoblasts encounter maternal immune cells. In this review, we focus on the role of maternal T cells and myeloid cells (macrophages, dendritic cells) in pregnancy and their interaction with trophoblasts. To retain immunologic tolerization, trophoblasts evade immune recognition by T cells and produce factors that modulate their phenotype and function. On top of that, the local environment at the maternal-fetal interface favors expansion of regulatory T cells. Macrophages and dendritic cells are essential in maintaining a healthy pregnancy. They produce soluble factors and act as antigen-presenting cells, thereby interacting with T cells. Herein, M2 macrophages, immature dendritic cells, CD4⁺ Th2 cells, and regulatory T cells represent an axis that maintains a local immune tolerant environment. We consider outstanding issues concerning these cell types and their pathways, which need to be addressed in future investigations. Data from recent single-cell sequencing experiments of the placental bed, to study heterogeneity of maternal immune cells and to predict cell-cell interactions, are discussed. Novel ways for long-term culturing of primary trophoblasts allow for cell-cell interaction studies in a functional way. Future directions should include study of the functionality of currently known and newly identified decidual immune cell subsets in healthy and complicated pregnancies, and their interaction with and modulation by trophoblast cells.

Regulatory T Cells in Pregnancy: It Is Not All About FoxP3

In pregnancy, the semi-allogeneic fetus needs to be tolerated by the mother's immune system. Regulatory T cells (Tregs) play a prominent role in this process. Novel technologies allow for in-depth phenotyping of previously unidentified immune cell subsets, which has resulted in the appreciation of a vast heterogeneity of Treg subsets. Similar to other immunological events, there appears to be great diversity within the Treg population during pregnancy, both at the maternal-fetal interface as in the peripheral blood. Different Treg subsets have distinct phenotypes and various ways of functioning. Furthermore, the frequency of individual Treg subsets varies throughout gestation and is altered in aberrant pregnancies. This suggests that distinct Treg subsets play a role at different time points of gestation and that their role in maintaining healthy pregnancy is crucial, as reflected for instance by their reduced frequency in women with recurrent pregnancy loss. Since pregnancy is essential for the existence of mankind, multiple immune regulatory mechanisms and cell types are likely at play to assure successful pregnancy. Therefore, it is important to understand the complete microenvironment of the decidua, preferably in the context of the whole immune cell repertoire of the pregnant woman. So far, most studies have focused on a single mechanism or cell type, which often is the FoxP3 positive regulatory T cell when studying immune regulation. In this review, we instead focus on the contribution of FoxP3 negative Treg subsets to the decidual microenvironment and their possible role in pregnancy complications. Their phenotype, function, and effect in pregnancy are discussed.

HLA-G and humanized mouse models as a novel therapeutic approach in transplantation

HLA-G is a nonclassical MHC-Class I molecule whose expression, along the feto-maternal barrier contributes towards tolerance of the semiallogeneic fetus during pregnancy. In light of its inhibitory properties, recent research has established HLA-G involvement in mechanisms responsible for directing allogeneic immune responses towards tolerance during allogeneic situations such as organ transplantation. Here, we critically review the data supporting the tolerogenic role of HLA-G in organ transplantation, the various factors influencing its expression, and the introduction of novel humanized mouse models that are one of the best approaches to assess the utility of HLA-G as a therapeutic tool in organ transplantation.