Impact of the MICA-129Met/Val Dimorphism on NKG2D-Mediated Biological Functions and Disease Risks

Oncolytic adenovirus coding for shedding-resistant MICA enhances immune responses against tumors

Cancer immunotherapies strive to overcome tumor-induced immune suppression and activate antitumor immune responses. Although cytotoxic T lymphocytes (CTLs) play a pivotal role in this process, natural killer (NK) cells have also demonstrated remarkable tumor-killing abilities, given their ability to discriminate tumor cells from normal cells and mediate specific antitumoral cytotoxicity. NK cells activation depends on a balance between activation and inhibition signals from several ligands/receptors. Among them, MICA/NKG2D axis is a master regulator of NK activation. MHC class I chain-related polypeptide A (MICA) expression is upregulated by many tumor cell lines and primary tumors and serves as a ligand for the activating NK group 2D (NKG2D) receptor on NK cells and subpopulations of T cells. However, cancer cells can cleave MICA, making it soluble and de-targeting tumor cells from NK cells, leading to tumor immune escape.In this study, we present ICOVIR15KK-MICAMut, an oncolytic adenovirus (OAdv) armed with a transgene encoding a non-cleavable MICA to promote NK-mediated cell-killing capacity and activate the immune response against cancer cells. We first demonstrated the correct MICA overexpression from infected cells. Moreover, our MICA-expressing OAdv promotes higher NK activation and killing capacity than the non-armed virus in vitro. In addition, the armed virus also demonstrated significant antitumor activity in immunodeficient mice in the presence of human PBMCs, indicating the activation of human NK cells. Finally, OAdv-MICA overexpression in immunocompetent tumor-bearing mice elicits tumor-specific immune response resulting in a greater tumor growth control.In summary, this study highlights the significance of NK cells in cancer immunotherapy and presents an innovative approach using a modified oncolytic virus to enhance NK cell activation and antitumor immune response. These findings suggest promising potential for future research and clinical applications.

The Significance of Major Histocompatibility Complex Class I Chain-related Molecule A in Solid Organ and Hematopoietic Stem Cell Transplantation: A Comprehensive Overview

Improving long-term allograft survival and minimizing recipient morbidity is of key importance in all of transplantation. Improved matching of classical HLA molecules and avoiding HLA donor-specific antibody has been a major focus; however, emerging data suggest the relevance of nonclassical HLA molecules, major histocompatibility complex class I chain-related gene A (MICA) and B, in transplant outcomes. The purpose of this review is to discuss the structure, function, polymorphisms, and genetics of the MICA molecule and relates this to clinical outcomes in solid organ and hematopoietic stem cell transplantation. The tools available for genotyping and antibody detection will be reviewed combined with a discussion of their shortcomings. Although data supporting the relevance of MICA molecules have accumulated, key knowledge gaps exist and should be addressed before widespread implementation of MICA testing for recipients pre- or posttransplantation.

Impact of MICA 3'UTR allelic variability on miRNA binding prediction, a bioinformatic approach

MicroRNAs (miRNAs) are small non-coding RNAs that participate as powerful genetic regulators. MiRNAs can interfere with cellular processes by interacting with a broad spectrum of target genes under physiological and pathological states, including cancer development and progression. Major histocompatibility complex major histocompatibility complex class I-related chain A (MICA) belongs to a family of proteins that bind the natural-killer group 2, member D (NKG2D) receptor on Natural Killer cells and other cytotoxic lymphocytes. MICA plays a crucial role in the host's innate immune response to several disease settings, including cancer. MICA harbors various single nucleotide polymorphisms (SNPs) located in its 3'-untranslated region (3'UTR), a characteristic that increases the complexity of MICA regulation, favoring its post-transcriptional modulation by miRNAs under physiological and pathological conditions. Here, we conducted an in-depth analysis of MICA 3'UTR sequences according to each MICA allele described to date using NCBI database. We also systematically evaluated interactions between miRNAs and their putative targets on MICA 3'UTR containing SNPs using in silico analysis. Our in silico results showed that MICA SNPs rs9266829, rs 1880, and rs9266825, located in the target sequence of miRNAs hsa-miR-106a-5p, hsa-miR-17-5p, hsa-miR-20a-5p, hsa-miR-20b-5p, hsa-miR-93, hsa-miR-1207.5p, and hsa-miR-711 could modify the binding free energy between -8.62 and -18.14 kcal/mol, which may affect the regulation of MICA expression. We believe that our results may provide a starting point for further exploration of miRNA regulatory effects depending on MICA allelic variability; they may also be a guide to conduct miRNA in silico analysis for other highly polymorphic genes.

The impact of NKG2A and NKG2D receptors and HLA-E and MICA ligands polymorphisms on post-transplant complications after paediatric allogeneic HSCT: a single-centre experience

Introduction: Natural Killer cells are the first subpopulation of lymphocytes that reconstitute after allogeneic haematopoietic stem cell transplantation (HSCT). Their activity is regulated by various receptor-ligand interactions, including stimulation of the activating NKG2D receptor by the MICA molecule, and inhibitory NKG2A receptor interacting with the HLA-E. In this study the research effort focused on the effect of selected NKG2A and NKG2D receptors and their ligands (HLA-E and MICA molecules) polymorphisms that may affect the pathomechanisms of post-transplant complications after HSCT in children. Methods: One hundred donor-recipient pairs from a single paediatric transplantation centre were investigated. Altogether six single nucleotide substitutions (NKG2A rs7301582; NKG2D rs1049174, rs1154831; HLA-E rs1264457; MICA rs1051792, rs1063635) were genotyped, and the influence of polymorphisms was analysed on acute and chronic graft-versus-host disease (GvHD), cytomegalovirus (CMV) infection incidence, disease relapse and survival. Results: The distribution of the evaluated polymorphisms did not differ between patients and their donors. The results showed a significant influence of HLA-E rs1264457 polymorphism in patients' HLA-E*01:01 allele, which was associated with increased risk of CMV infection (p = 0.050), especially in children positive for CMV IgG before transplantation (p = 0.001). Furthermore, the effect of HLA-E*01:01 allele on CMV infections was more evident in children above the age of 7 years (p = 0.031). Strong tendencies (0.05 < p < 0.10) towards association with the risk of acute GvHD were also observed for the NKG2A or MICA polymorphisms of the recipients. In addition, NKG2D rs1154831 AA and MICA rs1063635 GG might play a protective role as they were not present in any recipient who died after transplantation. Conclusion: In summary, there is emerging evidence that genotyping results of NKG2 receptors and their ligands, may have prognostic value for the outcome of paediatric allogeneic HSCT, but more extensive studies performed on larger groups of donors and transplant recipients are required to confirm these observations.

Associations between MICA and MICB Genetic Variants, Protein Levels, and Colorectal Cancer: Atherosclerosis Risk in Communities (ARIC)

BACKGROUND

The MHC class I chain-related protein A (MICA) and protein B (MICB) participate in tumor immunosurveillance and may be important in colorectal cancer, but have not been examined in colorectal cancer development.

METHODS

sMICA and sMICB blood levels were measured by SomaScan in Visit 2 (1990-92, baseline) and Visit 3 (1993-95) samples in cancer-free participants in the Atherosclerosis Risk in Communities Study. We selected rs1051792, rs1063635, rs2516448, rs3763288, rs1131896, rs2596542, and rs2395029 that were located in or in the vicinity of MICA or MICB and were associated with cancer or autoimmune diseases in published studies. SNPs were genotyped by the Affymetrix Genome-Wide Human SNP Array. We applied linear and Cox proportional hazards regressions to examine the associations of preselected SNPs with sMICA and sMICB levels and colorectal cancer risk (236 colorectal cancers, 8,609 participants) and of sMICA and sMICB levels with colorectal cancer risk (312 colorectal cancers, 10,834 participants). In genetic analyses, estimates adjusted for ancestry markers were meta-analyzed.

RESULTS

Rs1051792-A, rs1063635-A, rs2516448-C, rs3763288-A, rs2596542-T, and rs2395029-G were significantly associated with decreased sMICA levels. Rs2395029-G, in the vicinity of MICA and MICB, was also associated with increased sMICB levels. Rs2596542-T was significantly associated with decreased colorectal cancer risk. Lower sMICA levels were associated with lower colorectal cancer risk in males (HR = 0.68; 95% confidence interval, 0.49-0.96) but not in females (Pinteraction = 0.08).

CONCLUSIONS

Rs2596542-T associated with lower sMICA levels was associated with decreased colorectal cancer risk. Lower sMICA levels were associated with lower colorectal cancer risk in males.

IMPACT

These findings support an importance of immunosurveillance in colorectal cancer.

MICA and MICB allele assortment in Finland

Genetic variation in the MICA and MICB genes located within the major histocompatibility complex region has been reported to be associated with transplantation outcome and susceptibility to autoimmune diseases and infections. Only limited data of polymorphism in these genes in different populations are available. We here report allelic variation at 2-field resolution and the haplotypes of the MICA and MICB genes in Finland (n = 1032 individuals), a north European population with historical bottleneck and founder effects. Altogether 24 MICA and 18 MICB alleles were found, forming 70 estimated MICA-MICB haplotypes. As compared to other populations frequency differences were found, for example, MICA*010:01 was found to be at an allele frequency of 0.133 in Finland which is higher than in other European populations (0.021-0.077), but close to Asian populations (0.151-0.220). Three novel alleles with amino acid change are described. The results demonstrate a relatively high level of polymorphism and population differences in MICA and MICB allele distribution.

Diseases association with the polymorphic major histocompatibility complex class I related chain a: MICA gene

The Major Histocompatibility Complex class I chain-related molecule A (MICA) genes encode a highly polymorphic glycoprotein among the cell surface antigens that trigger an immune response after allograft transplantation. It is encoded by the MICA gene, a member of the glycosylated MIC genes. Discovered in 1994, the MICA gene is located within the MHC class I region. Moreover, its biological function is achieved through the interaction with the NKG2D receptor. Unlike the classical HLA molecules, MICA protein is not associated with β2- microglobulin nor binds peptides. MICA gene expression may result in a cytotoxic response and IFN-γ secretion through the up-regulation by heat shock proteins in response to infection (Human Cytomegalovirus HCMV), mediated by NKG2D-expressing cells. Anti-MICA antibodies were identified as significant risk factors for antibody mediated rejection after being detected in sera of patients with graft rejection. In addition, soluble MICA proteins (sMICA) has been detected in the serum of transplant recipients with cancers. Furthermore, the association of MICA polymorphisms with infectious diseases, various autoimmune diseases, cancer, and allograft rejection or graft-versus-host disease (GVHD) has been studied. Moreover, numerous advanced disease studies centered on MICA polymorphism are independent of HLA association. In this review, we discussed the up-to-date data about MICA and the association of MICA polymorphism with infections, autoimmune diseases, graft-versus-host disease, and cancer.

Major Histocompatibility Complex Class I Chain-Related α (MICA) STR Polymorphisms in COVID-19 Patients

The SARS-CoV-2 disease presents different phenotypes of severity. Comorbidities, age, and being overweight are well established risk factors for severe disease. However, innate immunity plays a key role in the early control of viral infections and may condition the gravity of COVID-19. Natural Killer (NK) cells are part of innate immunity and are important in the control of virus infection by killing infected cells and participating in the development of adaptive immunity. Therefore, we studied the short tandem repeat (STR) transmembrane polymorphisms of the major histocompatibility complex class I chain-related A (MICA), an NKG2D ligand that induces activation of NK cells, among other cells. We compared the alleles and genotypes of MICA in COVID-19 patients versus healthy controls and analyzed their relation to disease severity. Our results indicate that the MICA*A9 allele is related to infection as well as to symptomatic disease but not to severe disease. The MICA*A9 allele may be a risk factor for SARS-CoV-2 infection and symptomatic disease.

Leveraging NKG2D Ligands in Immuno-Oncology

Immune checkpoint inhibitors (ICI) revolutionized the field of immuno-oncology and opened new avenues towards the development of novel assets to achieve durable immune control of cancer. Yet, the presence of tumor immune evasion mechanisms represents a challenge for the development of efficient treatment options. Therefore, combination therapies are taking the center of the stage in immuno-oncology. Such combination therapies should boost anti-tumor immune responses and/or target tumor immune escape mechanisms, especially those created by major players in the tumor microenvironment (TME) such as tumor-associated macrophages (TAM). Natural killer (NK) cells were recently positioned at the forefront of many immunotherapy strategies, and several new approaches are being designed to fully exploit NK cell antitumor potential. One of the most relevant NK cell-activating receptors is NKG2D, a receptor that recognizes 8 different NKG2D ligands (NKG2DL), including MICA and MICB. MICA and MICB are poorly expressed on normal cells but become upregulated on the surface of damaged, transformed or infected cells as a result of post-transcriptional or post-translational mechanisms and intracellular pathways. Their engagement of NKG2D triggers NK cell effector functions. Also, MICA/B are polymorphic and such polymorphism affects functional responses through regulation of their cell-surface expression, intracellular trafficking, shedding of soluble immunosuppressive isoforms, or the affinity of NKG2D interaction. Although immunotherapeutic approaches that target the NKG2D-NKG2DL axis are under investigation, several tumor immune escape mechanisms account for reduced cell surface expression of NKG2DL and contribute to tumor immune escape. Also, NKG2DL polymorphism determines functional NKG2D-dependent responses, thus representing an additional challenge for leveraging NKG2DL in immuno-oncology. In this review, we discuss strategies to boost MICA/B expression and/or inhibit their shedding and propose that combination strategies that target MICA/B with antibodies and strategies aimed at promoting their upregulation on tumor cells or at reprograming TAM into pro-inflammatory macrophages and remodeling of the TME, emerge as frontrunners in immuno-oncology because they may unleash the antitumor effector functions of NK cells and cytotoxic CD8 T cells (CTL). Pursuing several of these pipelines might lead to innovative modalities of immunotherapy for the treatment of a wide range of cancer patients.

MICA*019 Allele and Soluble MICA as Biomarkers for Ankylosing Spondylitis in Taiwanese

MICA (major histocompatibility complex class I chain-related gene A) interacts with NKG2D on immune cells to regulate host immune responses. We aimed to determine whether MICA alleles are associated with AS susceptibility in Taiwanese. MICA alleles were determined through haplotype analyses of major MICA coding SNP (cSNP) data from 895 AS patients and 896 normal healthy controls in Taiwan. The distributions of MICA alleles were compared between AS patients and normal healthy controls and among AS patients, stratified by clinical characteristics. ELISA was used to determine soluble MICA (sMICA) levels in serum of AS patients and healthy controls. Stable cell lines expressing four major MICA alleles (MICA*002, MICA*008, MICA*010 and MICA*019) in Taiwanese were used for biological analyses. We found that MICA*019 is the only major MICA allele significantly associated with AS susceptibility (P_FDR = 2.25 × 10⁻¹¹⁵; OR, 14.90; 95% CI, 11.83–18.77) in Taiwanese. In addition, the MICA*019 allele is associated with syndesmophyte formation (P_FDR = 0.0017; OR, 1.69; 95% CI, 1.29–2.22) and HLA-B27 positivity (P_FDR = 1.45 × 10⁻³³; OR, 28.79; 95% CI, 16.83–49.26) in AS patients. Serum sMICA levels were significantly increased in AS patients as compared to healthy controls. Additionally, MICA*019 homozygous subjects produced the highest levels of sMICA, compared to donors with other genotypes. Furthermore, in vitro experiments revealed that cells expressing MICA*019 produced the highest level of sMICA, as compared to other major MICA alleles. In summary, the MICA*019 allele, producing the highest levels of sMICA, is a significant risk factor for AS and syndesmophyte formation in Taiwanese. Our data indicate that a high level of sMICA is a biomarker for AS.

Associations of high-resolution-typing-defined MICA and MICB polymorphisms, and the levels of soluble MICA and MICB with Oral Squamous Cell Carcinoma in Bulgarian patients

BACKGROUND

Oral Squamous Cell Carcinoma (OSCC) is a malignancy characterized by an aggressive tumor growth and significant mortality. Clarifying mechanisms responsible for immunomodulation are among the main challenges for the development of personalized approaches for the management of patients with Oral Squamous Cell Carcinoma. The aim of the present study was to analyze the relevance of MICA and MICB to Oral Squamous Cell Carcinoma pathogenesis focusing on allele polymorphisms and the levels of soluble MICA and MICB molecules.

MATERIALS AND METHODS

73 patients diagnosed with Oral Squamous Cell Carcinoma and 149 healthy controls from the Bulgarian population were included in the study. MICA and MICB polymorphism was analyzed at high-resolution level using Next-Generation Sequencing. Serum levels of soluble MICA and MICB molecules were measured by ELISA.

RESULTS

Our results show significant protective association with MICB*002:01, while relatively rare alleles MICB*018, *019, and *020 were observed with statistically significant increased frequency in Oral Squamous Cell Carcinoma patients compared to controls. Additionally, a predisposing association was observed for MICA*008:01-MICB*019 haplotype. A correlation analysis between functionally relevant MICA polymorphisms and sMICA showed that homozygosity for MICA-A5.1 or 129Val in OSCC patients was associated with significantly higher serum levels of sMICA.

CONCLUSION

This is the first study showing significant associations between MICB alleles and Oral Squamous Cell Carcinoma and suggesting the possible role of MICB in immunosurveillance in Oral Squamous Cell Carcinoma development. Observed correlations between the levels of soluble MICA molecules and functionally relevant polymorphisms might represent a further step toward a better understanding of molecular mechanisms of Oral Squamous Cell Carcinoma and developing strategies for therapeutic targeting harnessing effective immunosurveillance.

Major Histocompatibility Complex Class I-Related Chain A (MICA) Allelic Variants Associate With Susceptibility and Prognosis of Gastric Cancer

Gastric cancer (GC) is the fifth most prevalent type of cancer worldwide. Gastric tumor cells express MICA protein, a ligand to NKG2D receptor that triggers natural killer (NK) cells effector functions for early tumor elimination. MICA gene is highly polymorphic, thus originating alleles that encode protein variants with a controversial role in cancer. The main goal of this work was to study MICA gene polymorphisms and their relationship with the susceptibility and prognosis of GC. Fifty patients with GC and 50 healthy volunteers were included in this study. MICA alleles were identified using Sanger sequencing methods. The analysis of MICA gene sequence revealed 13 MICA sequences and 5 MICA-short tandem repeats (STR) alleles in the studied cohorts We identified MICA^*002 (^*A9) as the most frequent allele in both, patients and controls, followed by MICA^*008 allele (^*A5.1). MICA^*009/049 allele was significantly associated with increased risk of GC (OR: 5.11 [95% CI: 1.39–18.74], p = 0.014). The analysis of MICA-STR alleles revealed a higher frequency of MICA^*A5 in healthy individuals than GC patients (OR = 0.34 [95% CI: 0.12–0.98], p = 0.046). Survival analysis after gastrectomy showed that patients with MICA^*002/002 or MICA^*002/004 alleles had significantly higher survival rates than those patients bearing MICA^*002/008 (p = 0.014) or MICA^*002/009 (MICA^*002/049) alleles (p = 0.040). The presence of threonine in the position MICA-181 (MICA^*009/049 allele) was more frequent in GC patients than controls (p = 0.023). Molecular analysis of MICA-181 showed that the presence of threonine provides greater mobility to the protein than arginine in the same position (MICA^*004), which could explain, at least in part, some immune evasion mechanisms developed by the tumor. In conclusion, our findings suggest that the study of MICA alleles is crucial to search for new therapeutic approaches and may be useful for the evaluation of risk and prognosis of GC and personalized therapy.

Shared epitope and polymorphism of MICA and NKG2D encoding genes in Greek and Polish patients with rheumatoid arthritis

The present study aimed to analyse and compare the distribution of MICA (rs1051792) and NKG2D/KLRK1 (rs1154831, rs1049174, rs2255336) polymorphisms in 61 Greek and 100 Polish patients with rheumatoid arthritis in relation to the presence of the HLA-DRB1 shared epitope and clinical parameters. Genotyping of selected polymorphism was performed using real-time PCR. HLA-DRB1 shared epitope alleles segregated differently in Greek and Polish patients but in both populations were detected in over 60% of cases. The rs1051792-A variant was more common among SE-positive Polish patients (p = 0.003) while the rs1049174-G allele was more frequently observed in Greeks than in Poles (p < 0.001). Moreover, among Greek patients, the rs1051792-GG homozygotes more frequently presented with anti-CCP antibodies and rheumatoid factor (RF), while carriers of the rs1049174-G variant and rs1154831-CC homozygotes were characterized by lower disease activity scores (p < 0.05 in all cases). These results imply that, in addition to the HLA-DRB1 SE alleles, MICA and NKG2D polymorphisms may also play a role in rheumatoid arthritis.

High-throughput genotyping of HLA-G, HLA-F, MICA, and MICB and analysis of frequency distributions in healthy blood donors from Catalonia

Similarly to HLA class I molecules, certain non-classical HLA class I genes and MHC class I polypeptide-related sequences A and B (MICA and MICB) act as ligands for KIR and NKG2D natural killer receptors. Although these genes are less polymorphic than HLA class I, few studies have analyzed their association with diseases. Information on allele frequencies in healthy donors is needed to map their distribution worldwide. This study is the first to analyze high-resolution HLA-G, HLA-F, MICA, and MICB allele frequencies using a novel high-throughput next generation-sequencing method. We analyzed DNA samples from 96 unrelated blood donors resident in Catalonia, Spain, and registered in the Barcelona Blood and Tissue Bank. Using the first two fields of the HLA nomenclature, we detected six HLA-G and two HLA-F alleles. The most frequent alleles were HLA-G*01:01 (77.08%) and HLA-F*01:01(84.90%). When the four fields were analyzed, we detected 16 and 10 alleles, respectively. Nineteen alleles were detected for MICA and 10 for MICB. The most frequent alleles in these cases were MICA*008:01 (16.15%) and MICB*005:02 (46.84%). All frequencies were in Hardy Weinberg equilibrium except MICA. We also estimated maximum-likelihood haplotype frequencies and calculated corresponding linkage disequilibrium (LD) values and found that few allele pairs were in disequilibrium. Strong LD between MICA and HLA-B (using data from a previous study) was observed. Our findings will be useful for guiding further research evaluating the functional role of these genes in different diseases and populations.

Genetic variants in NKG2D axis and susceptibility to Epstein-Barr virus-induced nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a rare epithelial carcinoma arising from the nasopharyngeal region. The pathogenesis of NPC is linked to Epstein-Barr virus (EBV) infection, although genetics and lifestyle factors appears to be also implicated. NKG2D is an immunoreceptor expressed by NK and T-cell subsets that recognizes MICA protein and other ligands on tumor cells. NKG2D interaction with MICA plays a role in the immunosurveillance to viruses and cancer.

METHODS

We investigated potential associations between functional polymorphisms in NKG2D and MICA genes with NPC susceptibility. We conducted a case-control study including 255 Vietnamese patients with EBV + non-differentiated NPC and 220 healthy controls.

RESULTS

We observed a significant association between the LNK/LNK genotype of rs1049174 (a variant associated with lower NKG2D receptor expression and reduced NK cell cytotoxicity) and increased susceptibility to NPC (adjusted OR = 1.66, 95% CI 1.07-2.59; p = 0.024). Similarly, the AA genotype of MICA rs2596542 was significantly associated with NPC (adjusted OR = 2.12; 95% CI 1.22-3.81; p = 0.009). In addition, tumor specimens of NPC patients with the AA genotype displayed a higher expression level of MICA proteins and showed higher EBV titers compared with tumor tissues from patients with the GG or GA genotypes. Higher EBV copy numbers were also observed in tumors with the A allele of MICA rs1051792 (also known as MICA-129 Met/Val) compared with those with the G allele; however, MICA rs1051792 variants were not associated with NPC susceptibility. These results suggest that genetic variants in components of the NKG2D axis may influence the individual susceptibility to EBV-induced NPC.

Convergent Evolution by Cancer and Viruses in Evading the NKG2D Immune Response

The natural killer group 2 member D (NKG2D) receptor and its family of NKG2D ligands (NKG2DLs) are key components in the innate immune system, triggering NK, γδ and CD8+ T cell-mediated immune responses. While surface NKG2DL are rarely found on healthy cells, expression is significantly increased in response to various types of cellular stress, viral infection, and tumour cell transformation. In order to evade immune-mediated cytotoxicity, both pathogenic viruses and cancer cells have evolved various mechanisms of subverting immune defences and preventing NKG2DL expression. Comparisons of the mechanisms employed following virus infection or malignant transformation reveal a pattern of converging evolution at many of the key regulatory steps involved in NKG2DL expression and subsequent immune responses. Exploring ways to target these shared steps in virus- and cancer-mediated immune evasion may provide new mechanistic insights and therapeutic opportunities, for example, using oncolytic virotherapy to re-engage the innate immune system towards cancer cells.

Review of Genetic Variation as a Predictive Biomarker for Chronic Graft-Versus-Host-Disease After Allogeneic Stem Cell Transplantation

Chronic graft-versus-host disease (cGvHD) is one of the major complications of allogeneic stem cell transplantation (HSCT). cGvHD is an autoimmune-like disorder affecting multiple organs and involves a dermatological rash, tissue inflammation and fibrosis. The incidence of cGvHD has been reported to be as high as 30% to 60% and there are currently no reliable tools for predicting the occurrence of cGvHD. There is therefore an important unmet clinical need for predictive biomarkers. The present review summarizes the state of the art for genetic variation as a predictive biomarker for cGvHD. We discuss three different modes of action for genetic variation in transplantation: genetic associations, genetic matching, and pharmacogenetics. The results indicate that currently, there are no genetic polymorphisms or genetic tools that can be reliably used as validated biomarkers for predicting cGvHD. A number of recommendations for future studies can be drawn. The majority of studies to date have been under-powered and included too few patients and genetic markers. Like in all complex multifactorial diseases, large collaborative genome-level studies are now needed to achieve reliable and unbiased results. Some of the candidate genes, in particular, CTLA4, HSPE, IL1R1, CCR6, FGFR1OP, and IL10, and some non-HLA variants in the HLA gene region have been replicated to be associated with cGvHD risk in independent studies. These associations should now be confirmed in large well-characterized cohorts with fine mapping. Some patients develop cGvHD despite very extensive immunosuppression and other treatments, indicating that the current therapeutic regimens may not always be effective enough. Hence, more studies on pharmacogenetics are also required. Moreover, all of these studies should be adjusted for diagnostic and clinical features of cGvHD. We conclude that future studies should focus on modern genome-level tools, such as machine learning, polygenic risk scores and genome-wide association study-transcription meta-analyses, instead of focusing on just single variants. The risk of cGvHD may be related to the summary level of immunogenetic differences, or whole genome histocompatibility between each donor-recipient pair. As the number of genome-wide analyses in HSCT is increasing, we are approaching an era where there will be sufficient data to incorporate these approaches in the near future.

MICA polymorphisms associated with antithyroid drug-induced agranulocytosis in the Chinese Han population

Background

Graves' disease (GD) is a clinical autoimmune thyroid disease. During the treatment of GD, antithyroid drug‐induced agranulocytosis (TIA) is a common and even life‐threatening adverse drug reaction. Previous studies suggested that susceptibility to TIA is strongly associated with HLA‐B*27:05, HLA‐B*38:02, and HLA‐DRB1*08:03 genetic variation and six single nucleotide polymorphisms (SNPs) in MICA genes.

Aims

The purpose of this study is to further study the associations between TIA, HLA‐B and MICA.

Materials & Methods

We genotyped MICA‐STR and MICA‐129 variants in 41 TIA and 308 control patients with GD and investigated the linkage effect among SNPs and short tandem repeat (STR) of MICA and HLA‐B alleles.

Results

The results showed that MICA*A5.1 was significantly associated with TIA (p = .007, odd ratio = 1.958, 95% confidence interval, 1.192–3.214). In addition, high linkage among MICA‐129 and six SNPs MICA and HLA‐B was detected, and two haplotypes (AAAACAAAAACGGCCTA and AACAAAAAAAACATTAA (p = 5.14E−07 and p = 3.42E−08, respectively)) were significantly associated with TIA. Furthermore, when we analyzed only MICA‐129 and HLA‐B separately, the haplotypes (AAAACAAAAAA with p = 2.49E−07 and AACAAAAAAAA with p = 2.14E−09) were identified with more significant effects. MICA‐129 was completely linked to six SNPs with haplotypes ACATTACA (p = 2.05E−05) significantly associated with TIA.

Conclusion

These data indicated that there was a significant linkage effect between MICA‐129 and other alleles, suggesting that they exert interactive effects as risk factors for the development of TIA.

Polymorphisms in Inflammatory Genes Modulate Clinical Complications in Patients With Sickle Cell Disease

Sickle cell disease (SCD), the most common monogenic disease worldwide, is marked by a phenotypic variability that is, to date, only partially understood. Because inflammation plays a major role in SCD pathophysiology, we hypothesized that single nucleotide polymorphisms (SNP) in genes encoding functionally important inflammatory proteins might modulate the occurrence of SCD complications. We assessed the association between 20 SNPs in genes encoding Toll-like receptors (TLR), NK cell receptors (NKG), histocompatibility leukocyte antigens (HLA), major histocompatibility complex class I polypeptide-related sequence A (MICA) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), and the occurrence of six SCD clinical complications (stroke, acute chest syndrome (ACS), leg ulcers, cholelithiasis, osteonecrosis, or retinopathy). This study was performed in a cohort of 500 patients. We found that the TLR2 rs4696480 TA, TLR2 rs3804099 CC, and HLA-G, rs9380142 AA genotypes were more frequent in patients who had fewer complications. Also, in logistic regression, the HLA-G rs9380142 G allele increased the risk of cholelithiasis (AG vs. AA, OR 1.57, 95%CI 1.16-2.15; GG vs. AA, OR 2.47, 95%CI 1.34-4.64; P = 0.02). For SNPs located in the NKG2D loci, in logistic regression, the A allele in three SNPs was associated with a lower frequency of retinopathy, namely, rs2246809 (AA vs. GG: OR 0.22, 95%CI 0.09-0.50; AG vs. GG: OR 0.47, 95%CI 0.31-0.71; P = 0.004, for patients of same origin), rs2617160 (AT vs. TT: OR 0.67, 95%CI 0.48-0.92; AA vs. TT: OR 0.45, 95%CI 0.23-0.84; P = 0.04), and rs2617169 (AA vs. TT: OR 0.33, 95%CI 0.13-0.82; AT vs. TT: OR 0.58, 95%CI 0.36-0.91, P = 0.049, in patients of same SCD genotype). These results, by uncovering susceptibility to, or protection against SCD complications, might contribute to a better understanding of the inflammatory pathways involved in SCD manifestations and to pave the way for the discovery of biomarkers that predict disease severity, which would improve SCD management.

MICAgen Mice Recapitulate the Highly Restricted but Activation-Inducible Expression of the Paradigmatic Human NKG2D Ligand MICA

NKG2D is a potent activating immunoreceptor expressed on nearly all cytotoxic lymphocytes promoting their cytotoxicity against self-cells expressing NKG2D ligands (NKG2DLs). NKG2DLs are MHC class I-like glycoproteins that usually are not expressed on "healthy" cells. Rather, their surface expression is induced by various forms of cellular stress, viral infection, or malignant transformation. Hence, cell surface NKG2DLs mark "dangerous" cells for elimination by cytotoxic lymphocytes and therefore can be considered as "kill-me" signals. In addition, NKG2DLs are up-regulated on activated leukocytes, which facilitates containment of immune responses. While the NKG2D receptor is conserved among mammals, NKG2DL genes have rapidly diversified during mammalian speciation, likely due to strong selective pressures exerted by species-specific pathogens. Consequently, NKG2DL genes are not conserved in man and mice, although their NKG2D-binding domains maintained structural homology. Human NKG2DLs comprise two members of the MIC (MICA/MICB) and six members of the ULBP family of glycoproteins (ULBP1-6) with MICA representing the best-studied human NKG2DLs by far. Many of these studies implicate a role of MICA in various malignant, infectious, or autoimmune diseases. However, conclusions from these studies often were limited in default of supporting in vivo experiments. Here, we report a MICA transgenic (MICAgen) mouse model that replicates central features of human MICA expression and function and, therefore, constitutes a novel tool to critically assess and extend conclusions from previous in vitro studies on MICA. Similarly to humans, MICA transcripts are broadly present in organs of MICAgen mice, while MICA glycoproteins are barely detectable. Upon activation, hematopoietic cells up-regulate and proteolytically shed surface MICA. Shed soluble MICA (sMICA) is also present in plasma of MICAgen mice but affects neither surface NKG2D expression of circulating NK cells nor their functional recognition of MICA-expressing tumor cells. Accordingly, MICAgen mice also show a delayed growth of MICA-expressing B16F10 tumors, not accompanied by an emergence of MICA-specific antibodies. Such immunotolerance for the xenoantigen MICA ideally suits MICAgen mice for anti-MICA-based immunotherapies. Altogether, MICAgen mice represent a valuable model to study regulation, function, disease relevance, and therapeutic targeting of MICA in vivo.

Association of MICA-129Met/Val polymorphism with clinical outcome of anti-TNF therapy and MICA serum levels in patients with rheumatoid arthritis

MHC class I polypeptide-related sequence A (MICA) is a stress-induced protein involved in activation of NK and T cells through interaction with NKG2D receptor. These molecules are atypically expressed in synovium of patients diagnosed with rheumatoid arthritis (RA). A total of 279 patients with RA, qualified to TNF-blockade therapy, were genotyped for MICA rs1051792 SNP. The effectiveness of anti-TNF agents was assessed with European League Against Rheumatism criteria. Significant relationship between MICA rs1051792 and outcome of TNF-blockade therapy has been found. The MICA rs1051792 GG genotype was overrepresented in patients non-responsive to anti-TNF drugs in comparison with other genotypes (p = 0.010). On the other hand, beneficial therapeutic response was more frequently detected among RA subjects possessing heterozygous genotype than those with homozygous genotypes (p = 0.003). Furthermore, increased MICA concentrations in serum were observed in patients possessing MICA rs1051792 GG genotype as compared with those with GA or AA genotypes (p = 1.8 × 10^-5). The results from this study indicate the potential influence of MICA rs1051792 polymorphism on modulation of therapeutic response to TNF-blockade treatment in RA.

MICA and KLRK1 genes and their impact in cervical intraepithelial neoplasia development in the southern Brazilian population

Cervical carcinoma and cervical intraepithelial neoplasia (CIN) are associated with persistent infection by oncogenic subtypes of HPV (Human Papillomavirus). Factors linked to immunity, genetics and others like oral contraceptive use, sexual behavior, coinfections with other microorganisms and smoking seem to influence the mechanisms that determine regression or progression to CIN and cervical cancer. We investigated the effect of the MHC class I chain-related gene A (MICA) and Killer Cell Lectin Like receptor K1 (KLRK1) genes on cervical cancer and CIN lesions susceptibility in a group of 195 patients from southern Brazil. There were found a significantly higher number of ex-smokers in the control group (p = 0.005). There were more oral contraceptives (OC) users in the patient group. MICA*008:01/04 allele showed a significant difference between patient and control groups (p = 0.03; OR = 0.63, 95% CI 0.41-0.96), as well as MICA*018:01(p = 0.004, OR = 0.15, 95% CI 0.03-0.64) and MICA*002:01/020 (p = 0.01; OR = 0.60, 95% CI 0.40-0.88). We also analyzed cases and controls according to the MICA-129 genotypes (Met/Val). There was found a difference (p = 0.02) with the Met/Val genotype in a higher frequency in controls and Val/Val and Val/MICA del at a higher frequency in the patient group. For the KLRK1 gene there was no significant difference between groups.

High-Throughput MICA/B Genotyping of Over Two Million Samples: Workflow and Allele Frequencies

MICA and MICB are ligands of the NKG2D receptor and thereby influence NK and T cell activity. MICA/B gene polymorphisms, expression levels and the amount of soluble MICA/B in the serum have been linked to autoimmune diseases, infections, and cancer. In hematopoietic stem cell transplantation, MICA matching between donor and patient has been correlated with reduced acute and chronic graft-vs.-host disease and improved survival. Hence, we developed an extremely cost-efficient high-throughput workflow for genotyping MICA/B for newly registered potential stem cell donors. Since mid-2017, we have genotyped over two million samples using NGS amplicon sequencing for MICA/B exons 2–5. In donors of German origin, MICA*008 is the most common MICA allele with a frequency of 42.3%. It is followed by MICA*002 (11.7%) and MICA*009 (8.8%). The three most common MICB alleles are MICB*005 (43.9%), MICB*004 (21.7%), and MICB*002 (18.9%). In general, MICB is less diverse than MICA and only 6 alleles, instead of 15, account for a cumulative allele frequency of 99.5%. In 0.5% of the samples we observed at least one allele of MICA or MICB which has so far not been reported to the IPD/IMGT-HLA database. By providing MICA/B typed voluntary donors, clinicians become empowered to include MICA/B into their donor selection process to further improve unrelated hematopoietic stem cell transplantation.

Influence of major histocompatibility complex class I chain-related gene A polymorphisms on cytomegalovirus disease after allogeneic hematopoietic cell transplantation

OBJECTIVE/BACKGROUND

Cytomegalovirus (CMV) infection and disease are common infectious complications after allogeneic hematopoietic cell transplantation (alloHCT). Major histocompatibility complex (MHC) class I chain-related gene A (MICA) is a ligand of the natural killer (NKG2D) receptor on immune effector cells that helps mediate NK cell alloreactivity. We hypothesized that MICA polymorphisms may influence CMV infection and disease incidence after alloHCT.

METHODS

We conducted a retrospective analysis of 423 adults at the Cleveland Clinic with hematologic malignancies treated with a matched related or unrelated donor alloHCT. CMV cases analyzed included a compositive of instances of viral copy replication above detection limits as well as any biopsy-proven tissue invasive disease episodes. Genotypes at the MICA-129 position have been categorized as weak (valine/valine; V/V), intermediate (methionine/valine; M/V), or strong (methionine/methionine; M/M) receptor affinity.

RESULTS

In multivariable analysis, V/V donor MICA-129 genotype was associated with CMV infection and disease (hazard ratio [HR] = 1.40; 95% confidence interval [CI], 1.00-1.96; p = .05), but not MICA mismatch (HR = 1.38; 95% CI, 0.83-2.29; p = .22). There was no association of acute or chronic GVHD with MICA donor-recipient mismatch (HR = 1.05; 95% 95% CI, 0.66-1.68; p = .83 and HR = 0.94; 95% CI, 0.51-1.76; p = .85, respectively) or V/V donor MICA-129 genotypes (HR = 1.02; 95% CI, 0.79-1.31; p = .89 and HR = 0.89; 95% CI, 0.65-1.22; p = .47, respectively).

CONCLUSION

These findings suggest that the donor MICA-129 V/V genotype with weak NKG2D receptor binding affinity is associated with an increased risk of CMV infection and disease after alloHCT.

Association between MICA rs2596542 Polymorphism with the Risk of Hepatocellular Carcinoma in Chronic Hepatitis C Patients

In this study we investigated the impact of rs2596542A/G single nucleotide polymorphism (SNP) in the major histocompatibility complex class I chain-related sequence A (MICA) gene on HCV-induced hepatocellular carcinoma (HCC) susceptibility in a Brazilian population. In total, 252 HCV-infected patients (98 with HCV-induced HCC and 154 non-malignant HCV-induced liver cirrhosis) were enrolled and 98 healthy control subjects (negative anti-HCV). The MICA rs2596542 SNP genotypes were determined by real-time PCR assay. No differences in MICA genotype frequencies between HCV-induced cirrhosis patients and controls were observed. However, genotype frequencies of rs2596542A/G SNP were statistically different between HCV-induced HCC patients and controls (p = 0.048), and also between HCC and HCV-induced cirrhosis patients (p = 0.039). The highest frequency of the rs2596542AA genotype was observed in HCC patients (31.6%) when compared with HCV-induced cirrhosis patients (18.8%) and healthy controls (19.4%). Also, rs2596542AA genotype carriers have an increased risk for HCC when compared to HCV-induced cirrhosis status [odds ratio (OR) = 1.99; 95% confidence interval (CI) = 1.06-3.74, p = 0.020)] and healthy individuals (OR = 1.92, 95% CI = 1.00-3.70, p = 0.049). Taken together our study suggest that MICA rs2596542 SNP impacts HCV-induced HCC susceptibility suggesting that genetic variants in MICA are of clinical relevance to hepatocarcinogenesis by impacting host immune response in chronic HCV infection.

NKG2D/NKG2-Ligand Pathway Offers New Opportunities in Cancer Treatment

The antitumor functions of NK cells are regulated by the integration of positive and negative signals triggered by numerous membrane receptors present on the NK cells themselves. Among the main activating receptors, NKG2D binds several stress-induced molecules on tumor targets. Engagement of NKG2D by its ligands (NKG2D-Ls) induces NK cell activation leading to production of cytokines and target cell lysis. These effects have therapeutic potential as NKG2D-Ls are widely expressed by solid tumors, whereas their expression in healthy cells is limited. Here, we describe the genetic and environmental factors regulating the NKG2D/NKG2D-L pathway in tumors. NKG2D-L expression is linked to cellular stress and cell proliferation, and has been associated with oncogenic mutations. Tumors have been found to alter their to NKG2D-L expression as they progress, which interferes with the antitumor function of the pathway. Nevertheless, this pathway could be advantageously exploited for cancer therapy. Various cancer treatments, including chemotherapy and targeted therapies, indirectly interfere with the cellular and soluble forms of NKG2D-Ls. In addition, NKG2D introduced into chimeric antigen receptors in T- and NK cells is a promising tumor immunotherapy approach.

Genetic Variants in Preeclampsia: Lessons From Studies in Latin-American Populations

Placental vascularization is a tightly regulated physiological process in which the maternal immune system plays a fundamental role. Vascularization of the maternal-placental interface involves a wide range of mechanisms primarily orchestrated by the fetal extravillous trophoblast and maternal immune cells. In a healthy pregnancy, an immune cross-talk between the mother and fetal cells results in the secretion of immunomodulatory mediators, apoptosis of specific cells, cellular differentiation/proliferation, angiogenesis, and vasculogenesis, altogether favoring a suitable microenvironment for the developing embryo. In the context of vasculopathy underlying common pregnancy disorders, it is believed that inefficient invasion of extravillous trophoblast cells in the endometrium leads to a poor placental blood supply, which, in turn, leads to decreased secretion of angiogenic factors, hypoxia, and inflammation commonly associated with preterm delivery, intrauterine growth restriction, and preeclampsia. In this review, we will focus on studies published by Latin American research groups, providing an extensive review of the role of genetic variants from candidate genes involved in a broad spectrum of biological processes underlying the pathophysiology of preeclampsia. In addition, we will discuss how these studies contribute to fill gaps in the current understanding of preeclampsia. Finally, we discuss some trending topics from important fields associated with pregnancy vascular disorders (e.g., epigenetics, transplantation biology, and non-coding RNAs) and underscore their possible implications in the pathophysiology of preeclampsia. As a result, these efforts are expected to give an overview of the extent of scientific research produced in Latin America and encourage multicentric collaborations by highlighted regional research groups involved in preeclampsia investigation.

A Valine Mismatch at Position 129 of MICA Is an Independent Predictor of Cytomegalovirus Infection and Acute Kidney Rejection in Simultaneous Pancreas⁻Kidney Transplantation Recipients

The polymorphic major histocompatibility complex class I chain-related molecule A (MICA) and its soluble form (sMICA) interact with activating receptor natural-killer group 2 member D (NKG2D) on natural-killer (NK) and T cells, thereby modifying immune responses to transplantation and infectious agents (e.g., cytomegalovirus). Two single-nucleotide polymorphisms (SNPs), rs2596538GA in the MICA promoter and rs1051792AG in the coding region (MICA-129Val/Met), influence MICA expression or binding to NKG2D, with MICA-129Met molecules showing higher receptor affinity. To investigate the impact of these SNPs on the occurrence of cytomegalovirus infection or acute rejection (AR) in individuals who underwent simultaneous pancreas⁻kidney transplantation (SPKT), 50 recipient-donor pairs were genotyped, and sMICA levels were measured during the first year post-transplantation. Recipients with a Val-mismatch (recipient Met/Met and donor Val/Met or Val/Val) showed shorter cytomegalovirus infection-free and shorter kidney AR-free survival. Additionally, Val mismatch was an independent predictor of cytomegalovirus infection and kidney AR in the first year post-transplantation. Interestingly, sMICA levels were lower in rs2596538AA and MICA129Met/Met-homozygous recipients. These results provide further evidence that genetic variants of MICA influence sMICA levels, and that Val mismatch at position 129 increases cytomegalovirus infection and kidney AR risk during the first year post-SPKT.

Functional Characterisation and Analysis of the Soluble NKG2D Ligand Repertoire Detected in Umbilical Cord Blood Plasma

We previously reported that cord blood plasma (CBP) contains significantly more soluble NKG2D ligands (sNKG2DLs), such as sMICB and sULBP1, than healthy adult plasma. Viral infection or malignant transformation upregulates expression of NKG2D ligand on affected cells, leading to NK group 2, member D (NKG2D)-mediated natural killer (NK) cell lysis. Conversely, sNKG2DL engagement of NKG2D decreases NK cell cytotoxicity leading to viral or tumour immune escape. We hypothesised that sNKG2DLs detected in CBP may represent an additional fetal–maternal tolerance mechanism. To further understand the role of sNKG2DL in pregnancy and individual contributions of the various ligand types, we carried out functional analysis using 181 CBP samples. To test the ability of CBP to suppress the function of NK cells in vitro, we measured expression of NKG2D, CD107a, and IFN-γ in NK cells from control donors after exposure to 181 individual CBP samples and characterised the sMICA, sMICB, and sULBP1 content of each one. Furthermore, to detect possible allelic differences between samples that may also affect function, we carried out umbilical cord blood typing for MHC class I-related chain A (MICA) and MHC class I-related chain B (MICB) coding and promoter allelic types. Strongest functional correlations related to increasing concentration of exosomal sULBP1, which was present in all CBP samples tested. In addition, common MICB alleles, such as MICB*005:02, resulted in increased concentration of sMICB. Interestingly, MICB*005:02 uniquely associated with eight different promoter types. Among promoter polymorphisms, P2 resulted in the highest expression of sMICB and P9 the least and was confirmed using luciferase reporter assays. Higher levels of sMICB associated with lower IFN-γ production, indicating that sMICB also suppressed NK cell function. We also examined the MICA functional dimorphism encoding methionine (met) or valine (val) at residue 129 associated with strong or weak NKG2D binding, respectively. Most sMICA associated with val/val, some with met/val but none with met/met and, counter-intuitively, the presence of sMICA in CBP increased NK cell cytotoxicity. We propose a model for fetal–maternal tolerance, whereby NK cell activity is limited by sULBP1 and sMICB in CBP. The release of 129val sMICA with weak NKG2D signalling may reduce the overall net suppressive signal and break tolerance thus allowing fetal NK cells to overcome immunological threats in utero.

The Donor Major Histocompatibility Complex Class I Chain-Related Molecule A Allele rs2596538 G Predicts Cytomegalovirus Viremia in Kidney Transplant Recipients

The interaction of major histocompatibility complex class I chain-related protein A (MICA) and its cognate activating receptor natural killer (NK) group 2 member D (NKG2D) receptor plays a significant role in viral immune control. In the context of kidney transplantation (KTx), cytomegalovirus (CMV) frequently causes severe complications. Hypothesizing that functional polymorphisms of the MICA/NKG2D axis might affect antiviral NK and T cell responses to CMV, we explored the association of the MICA-129 Met/Val single nucleotide polymorphism (SNP) (affecting the binding affinity of MICA with the NKG2D receptor), the MICA rs2596538 G/A SNP (influencing MICA transcription), and the NKG2D rs1049174 G/C SNP (determining the cytotoxic potential of effector cells) with the clinical outcome of CMV during the first year after KTx in a cohort of 181 kidney donor-recipients pairs. Univariate analyses identified the donor MICA rs2596538 G allele status as a protective prognostic determinant for CMV disease. In addition to the well-known prognostic factors CMV high-risk sero-status of patients and the application of lymphocyte-depleting drugs, the donor MICA rs2596538 G allele carrier status was confirmed by multivariate analyses as novel-independent factor predicting the development of CMV infection/disease during the first year after KTx. The results of our study emphasize the clinical importance of the MICA/NKG2D axis in CMV control in KTx and point out that the potential MICA transcription in the donor allograft is of clinically relevant importance for CMV immune control in this allogeneic situation. Furthermore, they provide substantial evidence that the donor MICA rs2596538 G allele carrier status is a promising genetic marker predicting CMV viremia after KTx. Thus, in the kidney transplant setting, donor MICA rs2596538 G may help to allow the future development of personal CMV approaches within a genetically predisposed patient cohort.

MICA-129 Dimorphism and Soluble MICA Are Associated With the Progression of Multiple Myeloma

Natural killer (NK) cells are immune innate effectors playing a pivotal role in the immunosurveillance of multiple myeloma (MM) since they are able to directly recognize and kill MM cells. In this regard, among activating receptors expressed by NK cells, NKG2D represents an important receptor for the recognition of MM cells, being its ligands expressed by tumor cells, and being able to trigger NK cell cytotoxicity. The MHC class I-related molecule A (MICA) is one of the NKG2D ligands; it is encoded by highly polymorphic genes and exists as membrane-bound and soluble isoforms. Soluble MICA (sMICA) is overexpressed in the serum of MM patients, and its levels correlate with tumor progression. Interestingly, a methionine (Met) to valine (Val) substitution at position 129 of the α2 heavy chain domain classifies the MICA alleles into strong (MICA-129Met) and weak (MICA-129Val) binders to NKG2D receptor. We addressed whether the genetic polymorphisms in the MICA-129 alleles could affect MICA release during MM progression. The frequencies of Val/Val, Val/Met, and Met/Met MICA-129 genotypes in a cohort of 137 MM patients were 36, 43, and 22%, respectively. Interestingly, patients characterized by a Val/Val genotype exhibited the highest levels of sMICA in the sera. In addition, analysis of the frequencies of MICA-129 genotypes among different MM disease states revealed that Val/Val patients had a significant higher frequency of relapse. Interestingly, NKG2D was downmodulated in NK cells derived from MICA-129Met/Met MM patients. Results obtained by structural modeling analysis suggested that the Met to Val dimorphism could affect the capacity of MICA to form an optimal template for NKG2D recognition. In conclusion, our findings indicate that the MICA-129Val/Val variant is associated with significantly higher levels of sMICA and the progression of MM, strongly suggesting that the usage of soluble MICA as prognostic marker has to be definitely combined with the patient MICA genotype.

How Mucosal Epithelia Deal with Stress: Role of NKG2D/NKG2D Ligands during Inflammation

Mucosal epithelia encounter both physicochemical and biological stress during their life and have evolved several mechanisms to deal with them, including regulation of immune cell functions. Stressed and damaged cells need to be cleared to control local inflammation and trigger tissue healing. Engagement of the activating NKG2D receptor is one of the most direct mechanisms involved in the recognition of stressed cells by the immune system. Indeed, injured cells promptly express NKG2D ligands that in turn mediate the activation of lymphocytes of both innate and adaptive arms of the immune system. This review focuses on different conditions that are able to modulate NKG2D ligand expression on the epithelia. Special attention is given to the mechanisms of immunosurveillance mediated by natural killer cells, which are finely tuned by NKG2D. Different types of stress, including viral and bacterial infections, chronic inflammation, and cigarette smoke exposure, are discussed as paradigmatic conditions for NKG2D ligand modulation, and the implications for tissue homeostasis are discussed.

Efficient Killing of Murine Pluripotent Stem Cells by Natural Killer (NK) Cells Requires Activation by Cytokines and Partly Depends on the Activating NK Receptor NKG2D

Natural killer (NK) cells play an important role as cytotoxic effector cells, which scan the organism for infected or tumorigenic cells. Conflicting data have been published whether NK cells can also kill allogeneic or even autologous pluripotent stem cells (PSCs) and which receptors are involved. A clarification of this question is relevant since an activity of NK cells against PSCs could reduce the risk of teratoma growth after transplantation of PSC-derived grafts. Therefore, the hypothesis has been tested that the activity of NK cells against PSCs depends on cytokine activation and specifically on the activating NK receptor NKG2D. It is shown that a subcutaneous injection of autologous iPSCs failed to activate NK cells against these iPSCs and can give rise to teratomas. In agreement with this result, several PSC lines, including two iPSC, two embryonic stem cell (ESC), and two so-called multipotent adult germline stem cell (maGSC) lines, were largely resistant against resting NK cells although differences in killing were found at low level. All PSC lines were killed by interleukin (IL)-2-activated NK cells, and maGSCs were better killed than the other PSC types. The PSCs expressed ligands of the activating NK receptor NKG2D and NKG2D-deficient NK cells from Klrk1^-/- mice were impaired in their cytotoxic activity against PSCs. The low-cytotoxic activity of resting NK cells was almost completely dependent on NKG2D. The cytotoxic activity of IL-2-activated NKG2D-deficient NK cells against PSCs was reduced, indicating that also other activating receptors on cytokine-activated NK cells must be engaged by ligands on PSCs. Thus, NKG2D is an important activating receptor involved in killing of murine PSCs. However, NK cells need to be activated by cytokines before they efficiently target PSCs and then also other NK receptors become relevant. These features of NK cells might be relevant for transplantation of PSC-derived grafts since NK cells have the capability to kill undifferentiated cells, which might be present in grafts in trace amounts.

Genetic Association of Hematopoietic Stem Cell Transplantation Outcome beyond Histocompatibility Genes

The outcome of hematopoietic stem cell transplantation (HSCT) is controlled by genetic factors among which the leukocyte antigen human leukocyte antigen (HLA) matching is most important. In addition, minor histocompatibility antigens and non-HLA gene polymorphisms in genes controlling immune responses are known to contribute to the risks associated with HSCT. Besides single-nucleotide polymorphisms (SNPs) in protein coding genes, SNPs in regulatory elements such as microRNAs (miRNAs) contribute to these genetic risks. However, genetic risks require for their realization the expression of the respective gene or miRNA. Thus, gene and miRNA expression studies may help to identify genes and SNPs that indeed affect the outcome of HSCT. In this review, we summarize gene expression profiling studies that were performed in recent years in both patients and animal models to identify genes regulated during HSCT. We discuss SNP–mRNA–miRNA regulatory networks and their contribution to the risks associated with HSCT in specific examples, including forkheadbox protein 3 and regulatory T cells, the role of the miR-155 and miR-146a regulatory network for graft-versus-host disease, and the function of MICA and its receptor NKG2D for the outcome of HSCT. These examples demonstrate how SNPs affect expression or function of proteins that modulate the alloimmune response and influence the outcome of HSCT. Specific miRNAs targeting these genes and directly affecting expression of mRNAs are identified. It might be valuable in the future to determine SNPs and to analyze miRNA and mRNA expression in parallel in cohorts of HSCT patients to further elucidate genetic risks of HSCT.