Soluble human leucocyte antigen-G molecules in peripheral blood haematopoietic stem cell transplantation: a specific role to prevent acute graft-versus-host disease and a link with regulatory T cells

Therapeutic Effects of HLA-G5 Overexpressing hAMSCs on aGVHD After Allo-HSCT: Involving in the Gut Microbiota at the Intestinal Barrier

Background

Acute graft-versus-host disease (aGVHD) initiated by intestinal barrier dysfunction and gut microbiota dysbiosis, remains one of the main obstacles for patients undergoing allogenic hematopoietic stem cell transplantation (allo-HSCT) to achieve good prognosis. Studies have suggested that mesenchymal stem cells (MSCs) can suppress immune responses and reduce inflammation, and human leukocyte antigen-G5 (HLA-G5) plays an important role in the immunomodulatory effects of MSCs, but very little is known about the potential mechanisms in aGVHD. Thus, we explored the effect of HLA-G5 on the immunosuppressive properties of human amnion MSCs (hAMSCs) and demonstrated its mechanism related to the gut microbiota at the intestinal barrier in aGVHD.

Methods

Patients undergoing allo-HSCT were enrolled to detect the levels of plasma-soluble HLA-G (sHLA-G) and regulatory T cells (Tregs). Humanized aGVHD mouse models were established and treated with hAMSCs or HLA-G5 overexpressing hAMSCs (ov-HLA-G5-hAMSCs) to explore the mechanism of HLA-G5 mediated immunosuppressive properties of hAMSCs and the effect of ov-HLA-G5-hAMSCs on the gut microbiota at the intestinal barrier in aGVHD.

Results

The plasma levels of sHLA-G on day +30 after allo-HSCT in aGVHD patients were lower than those in patients without aGVHD, and the sHLA-G levels were positively correlated with Tregs percentages. ov-HLA-G5-hAMSCs had the potential to inhibit the expansion of CD3+CD4+ T and CD3+CD8+ T cells and promote Tregs differentiation, suppress proinflammatory cytokine secretion but promote anti-inflammatory cytokines release. Besides, ov-HLA-G5-hAMSCs also could reverse the intestinal barrier dysfunction and gut microbiota dysbiosis in aGVHD.

Conclusion

We demonstrated that HLA-G might work with Tregs to create a regulatory network together to reduce the occurrence of aGVHD. HLA-G5 mediated hAMSCs to exert higher immunosuppressive properties in vivo and reverse the immune imbalance caused by T lymphocytes and cytokines. Furthermore, HLA-G5 overexpressing hAMSCs could restore gut microbiota and intestinal barriers, thereby ameliorating aGVHD.

The association between genetic variants at 3'-UTR and 5'-URR of HLA-G gene and the clinical outcomes of patients with leukemia receiving hematopoietic stem cell transplantation

In addition to the classical human leukocyte antigen (HLA) genes, the outcomes of post-hematopoietic stem cell transplantation (HSCT) are associated with human leukocyte antigen (HLA)-related genes and non-HLA genes involved in immune regulation. HLA-G gene plays an important role in immune tolerance, assisting immune escape of tumor cells, and decrease of transplant rejection. In this study, we explored the association of genetic variants at the 3'-untranslated region (3'-UTR) and 5'-upstream regulatory region (5'-URR) of HLA-G gene with the adverse outcomes of patients with leukemia receiving HSCT. The genomic DNAs of 164 patients who had acute leukemia and received HSCT were collected for analysis. Nine single nucleotide polymorphisms (SNPs) and six haplotypes in the 3'-UTR and 27 SNPs and 6 haplotypes in the 5'-URR were selected to investigate their relationship with the development of adverse outcomes for patients receiving HSCT, including mortality, relapse, and graft-versus-host disease. Our results revealed that two SNPs (rs371194629 and rs9380142) and one haplotype (UTR-3) located in the 3'-UTR and two SNPs (rs3823321 and rs1736934) and one haplotype (G0104a) located in the 5'-URR of HLA-G were associated with the occurrence of chronic GVHD or development of any forms of GVHD. No SNP was found to associate with the occurrence of mortality and relapse for patients receiving HSCT. These SNPs and haplotypes may play important roles in regulating immune tolerance of allografts post-HSCT that can be used to predict the risk of poor outcomes after receiving HSCT and giving preventive treatment to patients on time.

Extended loci histocompatibility matching in HSCT-Going beyond classical HLA

Unrelated haematopoietic stem cell transplantation (HSCT) has evolved from an experimental protocol to a potentially curative first-line treatment in a variety of haematologic malignancies. The continuous refinement of treatment protocols and supportive care paired with ongoing achievements in the technological field of histocompatibility testing enabled this transformation. Without a doubt, HLA matching is still the foremost criterion for donor selection in unrelated HSCT. However, HSCT-related treatment complications still occur frequently, often resulting in patients suffering severely or even dying as a consequence of such complications. Current literature indicates that other immune system modulating factors may play a role in the setting of HSCT. In this review, we discuss the current clinical evidence of a possible influence of nonclassical HLA antigens HLA-E, HLA-F, and HLA-G as well as the HLA-like molecules MICA and MICB, in HSCT.

Immunomodulating functions of human leukocyte antigen-G and its role in graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapeutic strategy to treat several hematological malignancies and non-hematological malignancies. However, graft-versus-host disease (GVHD) is a frequent and serious transplant-related complication which dramatically restrains the curative effect of allo-HSCT and a significant cause of morbidity and mortality in allogeneic HCT recipients. Effective prevention of GVHD mainly depends on the induction of peripheral immune tolerance. Human leukocyte antigen-G (HLA-G) is a non-classical MHC class I molecule with a strong immunosuppressive function, which plays a prominent role in immune tolerance. HLA-G triggers different reactions depending on the activation state of the immune cells and system. It also exerts a long-term immune tolerance mechanism by inducing regulatory cells. In this present review, we demonstrate the immunomodulatory properties of human leukocyte antigen-G and highlight the role of HLA-G as an immune regulator of GVHD. Furthermore, HLA-G could also serve as a good predictor of GVHD and represent a new therapeutic target for GVHD.

Stem cells and COVID-19: are the human amniotic cells a new hope for therapies against the SARS-CoV-2 virus?

A new coronavirus respiratory disease (COVID-19) caused by the SARS-CoV-2 virus, surprised the entire world, producing social, economic, and health problems. The COVID-19 triggers a lung infection with a multiple proinflammatory cytokine storm in severe patients. Without effective and safe treatments, COVID-19 has killed thousands of people, becoming a pandemic. Stem cells have been suggested as a therapy for lung-related diseases. In particular, mesenchymal stem cells (MSCs) have been successfully tested in some clinical trials in patients with COVID-19. The encouraging results positioned MSCs as a possible cell therapy for COVID-19. The amniotic membrane from the human placenta at term is a valuable stem cell source, including human amniotic epithelial cells (hAECs) and human mesenchymal stromal cells (hAMSCs). Interestingly, amnion cells have immunoregulatory, regenerative, and anti-inflammatory properties. Moreover, hAECs and hAMSCs have been used both in preclinical studies and in clinical trials against respiratory diseases. They have reduced the inflammatory response and restored the pulmonary tissue architecture in lung injury in vivo models. Here, we review the existing data about the stem cells use for COVID-19 treatment, including the ongoing clinical trials. We also consider the non-cellular therapies that are being applied. Finally, we discuss the human amniotic membrane cells use in patients who suffer from immune/inflammatory lung diseases and hypothesize their possible use as a successful treatment against COVID-19.

Human Amniotic Epithelial Stem Cells: A Promising Seed Cell for Clinical Applications

Perinatal stem cells have been regarded as an attractive and available cell source for medical research and clinical trials in recent years. Multiple stem cell types have been identified in the human placenta. Recent advances in knowledge on placental stem cells have revealed that human amniotic epithelial stem cells (hAESCs) have obvious advantages and can be used as a novel potential cell source for cellular therapy and clinical application. hAESCs are known to possess stem-cell-like plasticity, immune-privilege, and paracrine properties. In addition, non-tumorigenicity and a lack of ethical concerns are two major advantages compared with embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). All of the characteristics mentioned above and other additional advantages, including easy accessibility and a non-invasive application procedure, make hAESCs a potential ideal cell type for use in both research and regenerative medicine in the near future. This review article summarizes current knowledge on the characteristics, therapeutic potential, clinical advances and future challenges of hAESCs in detail.

Umbilical cord blood-derived mesenchymal stromal cells promote myeloid-derived suppressor cell proliferation by secreting HLA-G to reduce acute graft-versus-host disease after hematopoietic stem cell transplantation

BACKGROUND AIMS

Mesenchymal stem cells (MSCs) use multiple mechanisms to constrain both innate and adaptive immune responses to prevent graft-versus-host disease (GVHD). Myeloid-derived suppressor cells (MDSCs), as a heterogeneous population of early myeloid progenitor cells originating from bone marrow, are a naturally occurring immune regulatory population associated with inhibition of ongoing inflammatory responses, indicating their potential for GVHD therapy. There is accumulating evidence that MSCs and MDSCs do not act independently, but rather establish crosstalk. However, the role of MSCs in MDSC expansion and activation in GVHD remains unexplored.

METHODS

In vitro experiments included 2 groups: peripheral blood mononuclear cells (PBMCs) after mobilization and human umbilical cord blood-derived MSCs (UCB-MSCs) co-cultured with PBMCs. The number and functional difference of MDSCs in PBMCs were determined by flow cytometry. The culture supernatants of co-cultured cells were analyzed to identify cytokines involved in MDSC proliferation. The relationship between MSCs and MDSCs was clarified in GVHD and graft-versus-leukemia (GVL) animal models.

RESULTS

In vitro experiments confirmed that UCB-MSCs secreted HLA-G protein to promote and maintain the proliferation of MDSCs in peripheral blood after granulocyte colony-stimulating factor mobilization, and UCB-MSCs mediated the function of MDSCs to inhibit the proliferation of T cells and promote the proliferation of regulatory T cells. UCB-MSCs overexpressing HLA-G induced MDSC production in recipient mice, improved the ability of MDSCs to suppress T cells and further reduced acute GVHD (aGVHD) symptoms and survival time without influencing GVL effects.

CONCLUSIONS

UCB-MSCs expanded MDSCs via HLA-G/Ig-like transcript 4, reducing the severity of aGVHD without affecting GVL. The immunosuppressive potential of MSCs for the treatment of aGVHD significantly affects the development of MDSCs, thereby consolidating the position of MSCs in the prevention and treatment of aGVHD.

Is there a role for HLA-G in the induction of regulatory T cells during the maintenance of a healthy pregnancy?

PROBLEM

Pregnancy remains an immune challenge for the uterus that has to adapt to a semi-allogeneic fetus using various regulatory mechanisms. Both HLA-G and regulatory T cells (CD4⁺  CD25⁺  FOXP3⁺  T_regs ) are upregulated in successful pregnancy, but not in abortion. It is unclear if HLA-G plays a role in the upregulation of regulatory cells.

METHOD OF STUDY

We measured the level of both sHLA-G and T_reg  cells in the blood of healthy pregnant multigravida, unexplained recurrent spontaneous abortions (URSA) and healthy non-pregnant and nulliparous females. We cultured peripheral blood lymphocytes of healthy non-pregnant multigravida females who never had an abortion with lymphocytes of their partners at ratio of 1:1, with and without sHLA-G to detect changes in number of T_reg  cells, or relevant cytokines.

RESULTS

Soluble HLA-G concentrations and T_reg  cells percentage were significantly lower in women with URSA as compared to healthy pregnant multigravida women and were comparable to healthy non-pregnant nulliparous women. Percentage of T_regs  increased between zero time and mixed lymphocyte cultures (MLC) in both cultures with and without recombinant sHLA-G but no significant difference between the two cultures. When stimulated with sHLA-G the mean extracellular IL-10 concentration was unchanged, while the mean INF-γ concentration was slightly higher with no significant difference. Intracellular TGF-β was higher in CD4⁺  cells after incubation with sHLA-G.

CONCLUSION

The results of this study are consistent with previous studies on the role of sHLA-G and T_reg  cells in inducing immune-tolerance in pregnancy. The results also suggest a possible role for HLA-G in the enrichment of T_reg  cells.

Effects of recombinant thrombomodulin therapy and soluble human leukocyte antigen-G levels during hematopoietic stem cell transplantation

BACKGROUND

Conditioning chemotherapies for hematopoietic stem cell transplantation (HSCT), especially those that include total body irradiation, can result in serious complications such as graft-versus-host disease (GVHD). Human leukocyte antigen G (HLA-G) is a non-classical class I molecule with multiple immunoregulatory functions.

METHODS

We measured interleukin (IL)-10, transforming growth factor (TGF)β₁, and soluble HLA-G (sHLA-G) in HSCT patients and examined the relationship between sHLA-G levels and acute GVHD (aGVHD). Additionally, we investigated the effect of recombinant soluble thrombomodulin (rTM) therapy on sHLA-G levels. Our study cohort included 135 patients who underwent allogeneic HSCT at several institutions in Japan.

RESULTS

Serum levels of IL-10 and TGFβ₁ exhibited no significant changes following HSCT. In contrast, levels of sHLA-G were significantly increased at days 21 and 28 post-HSCT. For patients with confirmed complications, the frequency of aGVHD was significantly lower in those with a > 2.8-fold increase in sHLA-G levels at day 28 relative to day 7 post-HSCT. sHLA-G levels in patients who received rTM therapy were significantly higher at days 21 and 28 post-HSCT compared with those in patients who did not receive rTM therapy.

CONCLUSION

These data suggest that HLA-G/sHLA-G participate in prevention of GVHD, and that rTM may prevent aGVHD following HSCT by promoting elevation of sHLA-G.

Stem cell characteristics and the therapeutic potential of amniotic epithelial cells

Multiple stem cell types can be isolated from the human placenta. Recent advances in stem cell biology have revealed that human amniotic epithelial cells (hAECs) are one of the perinatal stem cells which possess embryonic stem cell-like differentiation capability and adult stem cell-like immunomodulatory properties. Unlike other types of placental stem cells, hAECs are derived from pluripotent epiblasts and maintain multilineage differentiation potential throughout gestation. Similar to mesenchymal stem cells, hAECs are also able to modulate the local immune response. These, and other properties, make hAECs attractive for cellular therapy. This review article summarizes current knowledge of stem cell characteristics and immunomodulatory properties of amniotic epithelial cells and aims to advance our understanding towards the goal of novel therapy development.

Role of major histocompatibility complex variation in graft-versus-host disease after hematopoietic cell transplantation

Graft-versus-host disease (GVHD) remains a significant potentially life-threatening complication of allogeneic hematopoietic cell transplantation (HCT). Since the discovery of the human leukocyte antigen (HLA) system over 50 years ago, significant advances have clarified the nature of HLA variation between transplant recipients and donors as a chief etiology of GVHD. New information on coding and non-coding gene variation and GVHD risk provides clinicians with options to consider selected mismatched donors when matched donors are not available. These advances have increased the availability of unrelated donors for patients in need of a transplant and have lowered the overall morbidity and mortality of HCT.

Mesenchymal stem cells upregulate Treg cells via sHLA-G in SLE patients

BACKGROUND

Soluble human leukocyte antigen-G (sHLA-G) is a non-classical HLA class I molecule, exhibiting strong immunosuppressive properties by inducing the differentiation of T regulatory cells (Treg). Mesenchymal stem cells (MSCs) transplantation alleviates disease progression in systemic lupus erythematosus (SLE) patients. However, the underlying mechanisms are largely unknown.

OBJECTIVES

To explore whether sHLA-G is involved in upregulating effects of MSCs on Treg, which contributes to therapeutic effects of MSCs transplantation in SLE.

METHODS

The serum sHLA-G levels of SLE patients and healthy controls were detected by ELISA. The percentages of peripheral blood CD4+ILT2+, CD8+ILT2+, CD19+ILT2+ cells and Treg cells were examined by flow cytometry. Ten patients with active SLE, refractory to conventional therapies, were infused with umbilical cord derived MSCs (UC-MSCs) and serum sHLA-G was measured 24h and 1month after infusion. The mice were divided into three groups: C57BL/6 mice, B6.MRL-Fas^lpr mice infused with phosphate buffer saline (PBS), and B6.MRL-Fas^lpr mice infused with bone marrow MSCs (BM-MSCs). Then, the concentrations of serum Qa-2 were detected. Peripheral blood mononuclear cells (PBMCs) were isolated from SLE patients and co-cultured with UC-MSCs for 3days at different ratios (50:1, 10:1, and 2:1) with or without HLA-G antibody, and the frequencies of CD4+CD25+Foxp3+ T cells were then determined by flow cytometry.

RESULTS

The concentrations of serum sHLA-G were comparable between SLE patients and healthy controls. However, there was a negative correlation between sHLA-G levels and SLE disease activity index (SLEDAI) scores in active SLE patients (SLEDAI>4). We found that serum sHLA-G levels were negatively correlated with blood urea nitrogen, serum creatinine and 24-hour urine protein in SLE patients. The sHLA-G levels were significantly lower in SLE patients with renal involvement than those without renal involvement. The expression of ILT2 on CD4+ T cells from SLE patients decreased significantly compared to that of healthy controls. A positive correlation between the frequencies of Treg and CD4+ILT2+ T cells was found in SLE patients. The levels of sHLA-G increased 24h post UC-MSCs transplantation. The concentrations of Qa-2 in BM-MSCs transplanted mice were significantly higher than those of control group. In vitro studies showed that MSCs increased the frequency of Treg cells in SLE patients in a dose-dependent manner, which was partly abrogated by the anti-HLA-G antibody.

CONCLUSIONS

Our results suggested that MSCs may alleviate SLE through upregulating Treg cells, which was partly dependent on sHLA-G.

Human amnion epithelial cells expressing HLA-G as novel cell-based treatment for liver disease

Despite routine liver transplantation and supporting medical therapies, thousands of patients currently wait for an organ and there is an unmet need for more refined and widely available regenerative strategies to treat liver diseases. Cell transplants attempt to maximize the potential for repair and/or regeneration in liver and other organs. Over 40years of laboratory pre-clinical research and 25years of clinical procedures have shown that certain liver diseases can be treated by the infusion of isolated cells (hepatocyte transplant). However, like organ transplants, hepatocyte transplant suffers from a paucity of tissues useful for cell production. Alternative sources have been investigated, yet with limited success. The tumorigenic potential of pluripotent stem cells together with their primitive level of hepatic differentiation, have limited the use of stem cell populations. Stem cell sources from human placenta, and the amnion tissue in particular are receiving renewed interest in the field of regenerative medicine. Unlike pluripotent stem cells, human amnion epithelial (AE) cells are easily available without ethical or religious concerns; they do not express telomerase and are not immortal or tumorigenic when transplanted. In addition, AE cells have been reported to express genes normally expressed in mature liver, when transplanted into the liver. Moreover, because of the possibility of an immune-privileged status related to their expression of HLA-G, it might be possible to transplant human AE cells without immunosuppression of the recipient.

Role of Pharmacogenetics in Hematopoietic Stem Cell Transplantation Outcome in Children

Hematopoietic stem cell transplantation (HSCT) is an established therapeutic procedure for several congenital and acquired disorders, both malignant and nonmalignant. Despite the great improvements in HSCT clinical practices over the last few decades, complications, such as graft vs. host disease (GVHD) and sinusoidal obstructive syndrome (SOS), are still largely unpredictable and remain the major causes of morbidity and mortality. Both donor and patient genetic background might influence the success of bone marrow transplantation and could at least partially explain the inter-individual variability in HSCT outcome. This review summarizes some of the recent studies on candidate gene polymorphisms in HSCT, with particular reference to pediatric cohorts. The interest is especially focused on pharmacogenetic variants affecting myeloablative and immunosuppressive drugs, although genetic traits involved in SOS susceptibility and transplant-related mortality are also reviewed.

Biology of the immunomodulatory molecule HLA-G in human liver diseases

The non-classical human leukocyte antigen-G (HLA-G), plays an important role in inducing tolerance, through its immunosuppressive effects on all types of immune cells. Immune tolerance is a key issue in the liver, both in liver homeostasis and in the response to liver injury or cancer. It would therefore appear likely that HLA-G plays an important role in liver diseases. Indeed, this molecule was recently shown to be produced by mast cells in the livers of patients infected with hepatitis C virus (HCV). Furthermore, the number of HLA-G-positive mast cells was significantly associated with fibrosis progression. The generation of immune tolerance is a role common to both HLA-G, as a molecule, and the liver, as an organ. This review provides a summary of the evidence implicating HLA-G in liver diseases. In the normal liver, HLA-G transcripts can be detected, but there is no HLA-G protein. However, HLA-G protein is detectable in the liver tissues and/or plasma of patients suffering from hepatocellular carcinoma, hepatitis B or C, or visceral leishmaniasis and in liver transplant recipients. The cells responsible for producing HLA-G differ between diseases. HLA-G expression is probably induced by microenvironmental factors, such as cytokines. The expression of HLA-G receptors, such as ILT2, ILT4, and KIRD2L4, on liver cells has yet to be investigated, but these receptors have been detected on all types of immune cells, and such cells are present in liver. The tolerogenic properties of HLA-G explain its deleterious effects in cancers and its beneficial effects in transplantation. Given the key role of HLA-G in immune tolerance, new therapeutic agents targeting HLA-G could be tested for the treatment of these diseases in the future.

HLA-G as a tolerogenic molecule in transplantation and pregnancy

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.

Total expression of HLA-G and TLR-9 in chronic lymphocytic leukemia patients

Suppressed immune status facilitates immune escape mechanisms that allow chronic lymphocytic leukemia cells to proliferate and expand. The expression of HLA-G could effectively inhibit the immune response. In immune response inhibitory signals follow activation of immune system which might be occur during bacterial or viral infection in CLL patients. In the current study we characterized two components of immune system, inhibitory molecule HLA-G with its receptor - CD85j and Toll-like receptor 9. The material was obtained from 41 CLL patients and 41 HV with similar median age. In CLL patients expression of intracellular and surface HLA-G and soluble HLA-G levels were significantly higher than in HV. We found higher expression of CD85j compared to HV and the positive correlation between expression of HLA-G and CD85j. All the CLL cells expressed TLR-9, and the level of expression positively correlated with expression of HLA-G and CD85j. Patients with higher expression of intracellular expression of TLR-9 have significantly longer treatment-free survival than patients with low expression of TLR-9 (57 months vs. 8 months, respectively). Summarizing in CLL we characterized activatory and inhibitory components of immune system that might be connected functionally. Analysis of TLR-9 expression might have additional prognostic value for CLL patients.

Soluble human leukocyte antigen G molecule expression in allogeneic hematopoietic stem cell transplantation: good predictor of acute graft-versus-host disease

BACKGROUND

Graft-versus-host disease (GVHD) remains a main complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Human leukocyte antigen G (HLA-G) is a non-classical class I molecule exerting multiple immunoregulatory functions. The aim of this study was to explore the relationship between soluble HLA-G (sHLA-G) and GVHD after allo-HSCT.

METHODS

The sHLA-G levels were examined using enzyme-linked immunosorbent assay in patients with hematological malignancies (n = 106) before transplantation, on days +15 and +30 after transplantation, as well as healthy volunteers (n = 10).

RESULTS

The levels of sHLA-G5, sHLA-G6 and sHLA-G7 in patients on days +15 and +30 after transplantation were all significantly higher than those before transplantation (all p ≤ 0.001). The increased levels of sHLA-G5 on days +15 and +30 after transplantation were both significantly higher in patients with grade 0-I acute GVHD (aGVHD) compared to those with grade II-IV aGVHD (both p < 0.001). The increased levels of sHLA-G5 on days +15 and +30 after transplantation were both negatively correlated with the severity of aGVHD (both p < 0.001).

CONCLUSION

sHLA-G5 might be a predictor of the occurrence and severity of aGVHD, which may help to establish individual prophylaxis against aGVHD and improve the survival for patients after allo-HSCT.

The plasma levels of soluble HLA-G molecules correlate directly with CD34+ cell concentration and HLA-G 14bp insertion/insertion polymorphism in cord blood donors

BACKGROUND

Cord blood provides haematopoietic stem cells for allogeneic transplantation and, thanks to the naivety of its immune system, has several advantages over other sources of stem cells. In the transplantation setting, the presence of immunosuppressive human leucocyte antigen (HLA)-G molecules has been advocated to prevent both rejection and Graft-versus-Host disease. HLA-G is physiologically expressed throughout pregnancy and is contained in cord blood at birth. Moreover, it has recently been reported that not only cord blood mesenchymal cells, but also CD34+ cell progenies produce soluble HLA-G (sHLA-G). We tried to identify the largest producer of sHLA-G among 85 healthy cord blood donors at Pavia Cord Blood Bank, correlating the sHLA-G concentration with the HLA-G 14bp insertion/deletion (INS/DEL) genotype and CD34+ cell concentration.

MATERIALS AND METHODS

We measured sHLA-G levels in 36 cord blood plasma stored at -20 °C for 2 months and 49 cord blood plasma stored at -196 °C for 4-6 years, by enzyme-linked immunosorbent assay. All cord blood donors were genotyped for the HLA-G 14bp INS/DEL polymorphism by polymerase chain reaction. For each cord blood unit, we measured the cell concentration by flow cytometry.

RESULTS

We did not find differences in sHLA-G levels between cord blood plasma aliquots stored for 4-6 years at -196 °C and cord blood plasma aliquots stored for 2 months at -20 °C. We observed a higher sHLA-G concentration in cord blood plasma donors who carried the HLA-G 14bp INS/INS genotype and had higher CD34+ cell concentrations (P=0.006).

DISCUSSION

This is the first report showing that the best cord blood stem cell donor is also the best sHLA-G producer, particularly if genetically characterized by the HLA-G 14bp INS/INS genotype. If the therapeutic role of sHLA-G molecules were to be finally established in the transplantation setting, our data suggest that cord blood plasma donors can provide a safe source of allogeneic sHLA-G immunosuppressive molecules ready for transfusion.

Soluble HLA-G molecules and HLA-G 14-base pair polymorphism after allogeneic hematopoietic cell transplantation

HLA-G 14-base pair (bp) polymorphism and soluble human leukocyte antigen G were previously reported to be implicated in allogeneic hematopoietic cell transplantation (allo-HSCT) outcome. However, soluble HLA-G blood levels and the 14-bp insertion-deletion polymorphism were separately assessed in the context of allo-HSCT. The aim of the present study was to examine the influence of the 14-bp insertion/deletion polymorphism of the HLA-G gene together with the soluble HLA-G plasma levels on allo-HSCT complications. We investigated the possible impact of HLA-G 14-bp polymorphism together with the pretransplantation and posttransplantation concentration of soluble HLA-G in 59 patients undergoing allo-HSCT. No association was found between the HLA-G 14-bp polymorphism, the soluble HLA-G level and acute graft-versus-host disease (GvHD), disease recurrence, or death. In contrast with previous reports the present data suggest a weak or negligible involvement of both 14-bp polymorphism on HLA-G gene and sHLA-G concentration in posttransplantation complications such as acute or chronic GvHD, relapse, or death.

Identification of a novel HLA-G+ regulatory population in blood: expansion after allogeneic transplantation and de novo HLA-G expression at graft-versus-host disease sites

BACKGROUND

The human leukocyte antigen-G (HLA-G) has been considered to be an important tolerogeneic molecule playing an essential role in maternal-fetal tolerance, which constitutes the perfect example of successful physiological immunotolerance of semi-allografts. In this context, we investigated the putative role of this molecule in the allogeneic hematopoietic cell transplantation setting.

DESIGN AND METHODS

The percentage of HLA-G(+) cells in peripheral blood of healthy donors and allo-transplanted patients was evaluated by flow cytometry. Their immunoregulatory and tolerogeneic properties were investigated in in vitro immunostimulatory and immunosuppression assays. Immunohistochemical analysis for HLA-G expression was performed in skin biopsies from allo-transplanted patients and correlated with the occurrence of graft-versus-host disease.

RESULTS

We identified a CD14(+)HLA-G(pos) population with an HLA-DR(low) phenotype and decreased in vitro immunostimulatory capacity circulating in peripheral blood of healthy individuals. Naturally occurring CD14(+)HLA-G(pos) cells suppressed T-cell responses and exerted an immunotolerogenic action on T cells by rendering them hyporesponsive and immunosuppressive in vitro. After allogeneic hematopoietic cell transplantation, HLA-G(pos) cells increase in blood. Interestingly, besides an increase in CD14(+)HLA-G(pos) cells, there was also a pronounced expansion of CD3(+)HLA-G(pos) cells. Of note, CD3(+)HLA-G(pos) and CD14(+)HLA-G(pos) cells from transplanted patients were suppressive in in vitro lymphoproliferation assays. Furthermore, we found an upregulation of HLA-G expression in skin specimens from transplanted patients that correlated with graft-versus-host disease. Inflammatory cells infiltrating the dermis of transplanted patients were also HLA-G(pos).

CONCLUSIONS

We report the presence of naturally occurring HLA-G(pos) monocytic cells with in vitro suppressive properties. HLA-G expressing regulatory blood cells were found in increased numbers after allogeneic transplantation. Epithelial cells in skin affected by graft-versus-host disease revealed elevated HLA-G expression.

Expression of soluble HLA-G in multiple myeloma patients and patients with renal failure

Human lymphocyte antigen-G (HLA-G) is an immunosuppressive molecule that induces functional silencing of immune component cells and can be responsible for immunosuppression in patients with multiple myeloma (MM). Immune dysfunction is an important feature of MM and leads to infections as well as may promote disease progression. Ninety-five patients were included in this study. In MM, the sHLA-G levels were increased when compared to healthy volunteers and the levels of sHLA-G correlated with concentration of creatinine. Interestingly, we detected high levels of sHLA-G in patients with renal insufficiency without any malignant disease but levels were lower than in MM.

Association of HLA-G low expressor genotype with severe acute graft-versus-host disease after sibling bone marrow transplantation

Background: Human leukocyte antigen-G (HLA-G) molecules play a prominent role in immune tolerance. Structurally similar to their classical HLA homologs, they are distinct by having high rate of polymorphism in the non-coding regions including a functionally relevant 14-base pair (bp) insertion/deletion (Ins/Del) allele in the 3′ untranslated region (3′UTR), rarely examined in a hematopoietic stem cell transplantation (HSCT) setting. Here, we analyzed the potential impact of HLA-G Ins/Del dimorphism on the incidence of acute graft-versus-host disease (aGvHD), transplant-related mortality (TRM), overall survival (OS), and incidence of relapse after HSCT using bone marrow (BM) as stem cell source from HLA-matched donors. Methods: One hundred fifty-seven sibling pairs, who had undergone HSCT, were studied for the distribution of the HLA-G 14 bp Ins/Del polymorphism using a polymerase chain reaction (PCR)-based technique. Potential genetic association with the incidence of aGvHD, TRM, and OS was analyzed by monovariate and multivariate analyses. Results: Monovariate analysis showed that the homozygous state for the 14-bp Ins allele is a risk factor for severe aGvHD (grade III and IV; P = 0.008), confirmed subsequently by multivariate analysis [hazard ratio (HR) = 3.5; 95% confidence interval (95%CI) = 1.3–9.5; P = 0.012]. We did not find any association between HLA-G polymorphism and the other studied complications. Conclusion: Our data suggest that the HLA-G low expressor 14 bp Ins allele constitutes a risk factor for the incidence of severe aGvHD in patients who received BM as stem cell source.

The tolerogenic interplay(s) among HLA-G, myeloid APCs, and regulatory cells

Myeloid antigen-presenting cells (APCs), regulatory cells, and the HLA-G molecule are involved in modulating immune responses and promoting tolerance. APCs are known to induce regulatory cells and to express HLA-G as well as 2 of its receptors; regulatory T cells can express and act through HLA-G; and HLA-G has been directly involved in the generation of regulatory cells. Thus, interplay(s) among HLA-G, APCs, and regulatory cells can be easily envisaged. However, despite a large body of evidence on the tolerogenic properties of HLA-G, APCs, and regulatory cells, little is known on how these tolerogenic players cooperate. In this review, we first focus on key aspects of the individual relationships between HLA-G, myeloid APCs, and regulatory cells. In its second part, we highlight recent work that gathers individual effects and demonstrates how intertwined the HLA-G/myeloid APCs/regulatory cell relationship is.

Plasma soluble human leukocyte antigen-G expression is a potential clinical biomarker in patients with hepatitis B virus infection

The significance of upregulated soluble human leukocyte antigen-G (sHLA-G) expression under various pathologic conditions has been discussed. In this study, we evaluated the potential significance of plasma sHLA-G expression in patients with hepatitis B virus (HBV) infection. The study included 90 acute hepatitis B patients (AHB), 131 chronic hepatitis B patients (CHB), 152 resolved hepatitis B individuals (RHB), and 129 normal controls. sHLA-G were determined using enzyme-linked immunosorbent assay. A receiver operating characteristic (ROC) curve was used to evaluate the feasibility of plasma sHLA-G as a biomarker for distinguishing patients with HBV infection. sHLA-G levels in AHB (median, 193.1 U/mL; p < 0.001), CHB (median, 324.6 U/mL; p < 0.001), and RHB (median, 14.8 U/mL; p = 0.006) patients was much higher than that in normal controls (median, 9.0 U/mL). A significant difference for sHLA-G levels was also observed between patients with HBV infection (AHB vs CHB, AHB vs RHB, and CHB vs RHB; all p < 0.001). The area under the ROC curve for sHLA-G levels was 1.000 (p < 0.001) for AHB, 0.993 (p < 0.001) for CHB, and 0.604 (p = 0.003) for RHB patients versus normal controls, respectively. Data also indicated that the percentage of CD4(+)CD25(+)FoxP3(+) T regulatory cells and HLA-G(+)CD14(+) monocytes was significantly increased in AHB and CHB patients compared with normal controls (all p < 0.001). Our findings indicated that induction of HLA-G expression may play a role in HBV immune evasion and sHLA-G levels could be a useful biomarker in HBV infection.

The role of HLA--G 14-bp polymorphism in allo-HSCT after short-term course MTX for GvHD prophylaxis

HLA-G molecules are HLA class Ib antigens characterized by tolerogenic and immunoinhibitory functions. The HLA-G 14-bp insertion/deletion (ins/del) polymorphism controls protein expression and seems to be implicated in both MTX treatment response and SCT outcome. The aim of our study is to evaluate the role of HLA-G 14 bp polymorphism in subjects affected by hematological malignancies undergoing allo-SCT and receiving MTX therapy for GvHD prophylaxis. We performed a retrospective analysis of HLA-G 14 bp polymorphism using a specific PCR in 47 recipients and in their respective donors, and evaluated the correlation with the incidence of aGvHD, OS and disease-free survival (DFS) after allo-SCT. We did not observe any correlation between this polymorphism and the risk of aGvHD occurrence. On the contrary, we found that the recipients with a 14 bp ins/14 bp ins genotype were characterized by a lower OS and DFS in univariate and multivariate analysis (OS=OR: 3.235; DFS=OR: 3.302). These data indicate a role for recipient HLA-G 14 bp polymorphism in allo-SCT immunotolerance status and follow-up.

Emerging topics and new perspectives on HLA-G

Following the Fifth International Conference on non-classical HLA-G antigens (HLA-G), held in Paris in July 2009, we selected some topics which focus on emerging aspects in the setting of HLA-G functions. In particular, HLA-G molecules could play a role in: (1) various inflammatory disorders, such as multiple sclerosis, intracerebral hemorrhage, gastrointestinal, skin and rheumatic diseases, and asthma, where they may act as immunoregulatory factors; (2) the mechanisms to escape immune surveillance utilized by several viruses, such as human cytomegalovirus, herpes simplex virus type 1, rabies virus, hepatitis C virus, influenza virus type A and human immunodeficiency virus 1 (HIV-1); and (3) cytokine/chemokine network and stem cell transplantation, since they seem to modulate cell migration by the downregulation of chemokine receptor expression and mesenchymal stem cell activity blocking of effector cell functions and the generation of regulatory T cells. However, the immunomodulatory circuits mediated by HLA-G proteins still remain to be clarified.

The role of HLA-G in immunity and hematopoiesis

The non-classical HLA class I molecule HLA-G was initially shown to play a major role in feto-maternal tolerance. Since this discovery, it has been established that HLA-G is a tolerogenic molecule which participates to the control of the immune response. In this review, we summarize the recent advances on (1) the multiple structures of HLA-G, which are closely associated with their role in the inhibition of NK cell cytotoxicity, (2) the factors that regulate the expression of HLA-G and its receptors, (3) the mechanism of action of HLA-G at the immunological synapse and through trogocytosis, and (4) the generation of suppressive cells through HLA-G. Moreover, we also review recent findings on the non-immunological functions of HLA-G in erythropoiesis and angiogenesis.

A simple method for identifying bone marrow mesenchymal stromal cells with a high immunosuppressive potential

BACKGROUND AIMS

The beneficial activity of mesenchymal stromal cells (MSC) in allogeneic hematopietic stem cell transplantation requires correct use in terms of cell dose and timing of infusion and the identification of biomarkers for selection. The immunosuppressive bone marrow (BM)-derived MSC (BM-MSC) functions have been associated with the production of soluble HLA-G molecules (sHLA-G) via interleukin (IL)-10. We have established a reliable method for evaluating BM-MSC HLA-G expression without the influence of peripheral blood mononuclear cells (PBMC).

METHODS

Thirteen BM-MSC from donors were activated with recombinant IL-10 or co-cultured with 10 different phytohemagglutinin (PHA)-treated PBMC (PHA-PBMC). Membrane-bound and sHLA-G expression was evaluated by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively; lymphoproliferation was measured by (methyl-(3)H)thymidine.

RESULTS

The results demonstrated the ability of IL-10 to stimulate both membrane-bound and sHLA-G production by BM-MSC. The levels of HLA-G expression induced by IL-10 in BM-MSC were associated with the inhibition of PHA-PBMC proliferation (sHLA-G, P = 0.0008, r = 0.9308; membrane HLA-G, P = 0.0005, r = 0.9502).

CONCLUSIONS

We propose the evaluation of sHLA-G production in IL-10-treated BM-MSC cultures as a possible marker of immunoregulatory function.

Biology of HLA-G in cancer: a candidate molecule for therapeutic intervention?

Although the expression of the non-classical HLA class I molecule HLA-G was first reported to be restricted to the fetal-maternal interface on the extravillous cytotrophoblasts, the distribution of HLA-G in normal tissues appears broader than originally described. HLA-G expression was found in embryonic tissues, in adult immune privileged organs, and in cells of the hematopoietic lineage. More interestingly, under pathophysiological conditions HLA-G antigens may be expressed on various types of malignant cells suggesting that HLA-G antigen expression is one strategy used by tumor cells to escape immune surveillance. In this article, we will focus on HLA-G expression in cancers of distinct histology and its association with the clinical course of diseases, on the underlying molecular mechanisms of impaired HLA-G expression, on the immune tolerant function of HLA-G in tumors, and on the use of membrane-bound and soluble HLA-G as a diagnostic or prognostic biomarker to identify tumors and to monitor disease stage, as well as on the use of HLA-G as a novel therapeutic target in cancer.

HLA-G: a human pregnancy-related immunomodulator

In human pregnancies mothers and their embryo/fetuses are invariably genetically different. Thus, attenuation of the adaptive maternal immune response, which is programmed to reject 'foreign' entities, is required for pregnancy to be initiated and maintained. Unexpectedly, given the propensity of the immune system to dispose of non-self entities, at least 50% of expected human pregnancies reliably go forward. This indicates that to a large extent, effective systems of tolerance have evolved. Although overlapping and redundant mechanisms of tolerance have been identified, production of HLA-G by trophoblast cells derived from the external trophectoderm layer of the blastocyst appears to be of major importance. At this point in time, no pregnancies in which all of the proteins derived from the HLA-G gene are absent have as yet been reported. Many studies have shown that both membrane-bound and soluble isoforms of the proteins derived from this HLA class Ib gene are produced by placental trophoblast cells, with consequences that include but are not restricted to immune suppression at the maternal-fetal interface. Here we report new studies that are leading to a better understanding of the HLA-G proteins, their unique structures, unusual modes of regulation, diverse functions, and potential for use in diagnostic and therapeutic procedures related to suboptimal fertility in women.