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

Hypomethylation-induced regulatory programs in T cells unveiled by transcriptomic analyses

Regulatory T cells (Tregs) are essential mediators of tolerance mitigating aberrant immune responses. While naturally occurring Treg (nTreg) development and function are directed by epigenetic events, induced Treg (iTreg) identity and mechanisms of action remain elusive. Mirroring the epigenetic circuits of nTregs, we and others have used hypomethylation agents (HAs) to ex vivo convert T cells into iTregs (HA-iTregs) and further showed that the suppressive properties of the HA-iTregs are predominantly confined in an emergent population, which de novo expresses the immunomodulatory molecule HLA-G, consequently providing a surface marker for isolation of the suppressive HA-iTreg compartment (G+ cells). We isolated the HA-induced G+ cells and their G- counterparts and employed high-throughput RNA-sequencing (RNA-seq) analyses to uncover the G+-specific transcriptomic changes guiding T cells toward a regulatory trajectory upon their exposure to HA. We found a distinct transcriptional upregulation of G+ cells accompanied by enrichment of immune-response-related pathways. Although single-cell RNA-seq profiling revealed regulatory G+ cells to have molecular features akin to nTregs, when assessed in conjunction with the comparative transcriptomic analysis and profiling of secreted cytokines against the non-suppressive G- cells, FOXP3 and other T-helper signatures appear to play a minor role in their suppressive phenotype. We found an ectopic expression of IDO-1 and CCL17/22 in G+ cells, denoting that in vitro exposure of T cells to HA may well unlock myeloid suppressor genes. This report provides transcriptional data shaping the molecular identity of a highly purified and potent HA-iTreg population and hints toward ectopic myeloid-specific molecular mechanisms mediating HA-iTreg function.

Epigenetic/genetic variations in CG-rich elements of immune-related genes contribute to food allergy development during childhood

BACKGROUND

Genetic areas of FOXP3 TSDR, human leukocyte antigen-G (HLA-G) upstream of CpG island 96, CpG41 and CpG73 islands of the HLA-DRB1 and HLA-DQB1 genes respectively, previously documented to display immune-modulatory properties, were subjected to epigenetic/genetic analysis to assess their influence in IgE-mediated food allergy (FA) development in children.

METHODS

Sixty-four orally challenged and IgE-tested food allergic subjects together with 44 controls were recruited. Targeted pyrosequencing analysis to detect DNA methylation status and genetic variations was utilized and experimental results obtained were analyzed by a statistical software platform and correlated to clinical data. Also, transcription factor (TF) binding sites in study areas were unmasked by the JASPAR prediction database.

RESULTS

Parents' smoking was significantly correlated with aberrant methylation patterns, regardless of food allergic or control status. HLA-G promoter region showed a trend for hypomethylation in food allergic subjects, with one of the CG sites displaying significantly decreased methylation values. Rs1233333, residing within the HLA-G promoter region preserved a protective role toward DNA methylation. Variable methylation patterns were recorded for CpG41 of the HLA-DRB1 gene and hypermethylation of the region was significantly correlated with the presence of single nucleotide polymorphisms (SNPs). TFs' recognition sites, located in studied genetic areas and exerting pivotal regulatory biological roles, are potentially affected by divergent DNA methylation status.

CONCLUSIONS

We propose that HLA-G expression is triggered by food-derived allergens, providing a Treg^{FoxP3-/HLA-G+} subpopulation generation to promote direct immune tolerance. Furthermore, clear evidence is provided for the underlying co-operation of genetic polymorphisms with epigenetic events, mainly at the CpG41 island of the HLA-DRB1 gene, which needs an extended investigation and elucidation.

HLA-G Expressing Immune Cells in Immune Mediated Diseases

HLA-G is a HLA class Ib antigen that possesses immunomodulatory properties. HLA-G-expressing CD4+ and CD8+ T lymphocytes, NK cells, monocytes, and dendritic cells with immunoregulatory functions are present in small percentages of patients with physiologic conditions. Quantitative and qualitative derangements of HLA-G+ immune cells have been detected in several conditions in which the immune system plays an important role, such as infectious, neoplastic, and autoimmune diseases as well as in complications from transplants and pregnancy. These observations strongly support the hypothesis that HLA-G+ immune cells may be implicated in the complex mechanisms underlying the pathogenesis of these disorders.

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.

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.

Tregs and kidney: From diabetic nephropathy to renal transplantation

Kidney transplantation is recognised as the most effective treatment for patients with end-stage renal disease (ESRD). Kidney transplantation continues to face several challenges including long-term graft and patient survival, and the side effects of immunosuppressive therapy. The tendency in kidney transplantation is to avoid the side effects of immunosuppresants and induce immune tolerance. Regulatory T-cells (Tregs) contribute to self-tolerance, tolerance to alloantigen and transplant tolerance, mainly by suppressing the activation and function of reactive effector T-cells. Additionally, Tregs are implicated in the pathogenesis of diabetes, which is the leading cause of ESRD, suggesting that these cells play a role both in the pathogenesis of chronic kidney disease and the induction of transplant tolerance. Several strategies to achieve immunological tolerance to grafts have been tested experimentally, and include combinations of co-stimulatory blockade pathways, T-cell depletion, in vivo Treg-induction and/or infusion of ex-vivo expanded Tregs. However, a successful regimen that induces transplant tolerance is not yet available for clinical application. This review brings together certain key studies on the role of Tregs in ESRD, diabetes and kidney transplantation, only to emphasize that many more studies are needed to elucidate the clinical significance and the therapeutic applications of Tregs.

CD4(+)HLA-G(+) regulatory T cells: Molecular signature and pathophysiological relevance

The regulation of potentially harmful immune responses by regulatory T (Treg) cells is essential for maintaining peripheral immune tolerance and homeostasis. Especially CD4(+) Treg cells have been regarded as pivotal regulators of autoreactive and inflammatory responses as well as inducers of immune tolerance by using a variety of immune suppressive mechanisms. Besides the well-known classical CD4(+)CD25(+)FoxP3(+) Treg cells, CD4(+) T cells expressing the immune tolerizing molecule human leukocyte antigen G (HLA-G) have been recently described as another potent thymus-derived Treg (tTreg) cell subset. Albeit both tTreg subsets share common molecular characteristics, the mechanisms of their immunosuppressive function differ fundamentally. Dysfunction and numerical abnormalities of classical CD4(+) tTreg cells have been implicated in the pathogenesis of several immune-mediated diseases such as multiple sclerosis (MS). Clearly, a deeper understanding of the various CD4(+) tTreg subsets and also the underlying mechanisms of impaired immune tolerance in these disorders are essential for the development of potential therapeutic strategies. This review focuses on the current knowledge on defining features and functioning of HLA-G(+)CD4(+) tTreg cells as well as their emerging role in various pathologies with special emphasis on the pathogenesis of MS. Furthermore, future research possibilities together with potential therapeutic applications are discussed.

CLL-cells induce IDOhi CD14+HLA-DRlo myeloid-derived suppressor cells that inhibit T-cell responses and promote TRegs

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population that shares certain characteristics including an aberrant myeloid phenotype and the ability to suppress T cells. MDSCs have been predominantly studied in malignant diseases and findings suggest involvement in tumor-associated immune suppression. Chronic lymphocytic leukemia (CLL) is the leukemia with the highest incidence among adults. Immune defects occur already at early disease stages and impact the clinical course. We assessed presence, frequency, association to other immune parameters, and functional properties of circulating CD14(+) cells lacking HLA-DR expression (HLA-DR(lo)) in patients with untreated CLL. These monocytic cells represent one of the best-defined human MDSC subsets. Frequency of CD14(+)HLA-DR(lo) cells was significantly increased in CLL patients. Furthermore, MDSCs suppressed in vitro T-cell activation and induced suppressive regulatory T cells (TRegs). The MDSC-mediated modulation of T cells could be attributed to their increased indoleamine 2,3-dioxygenase (IDO) activity. CLL cells induced IDO(hi) MDSCs from healthy donor monocytes suggesting bidirectional crosstalk between CLL-cells, MDSCs, and TRegs. Overall, we identified a MDSC population that expands in CLL. The exact mechanisms responsible for such accumulation remain to be elucidated and it will be of interest to test whether antagonizing suppressive functions of CLL MDSCs could represent a mean for enhancing immune responses.

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.