Association between human leukocyte antigen-G 14-bp insertion/deletion polymorphism and cancer risk: A meta-analysis and systematic review

The 14-bp insertion/deletion as a promising gene polymorphism to understand cancer risk: Evidence from a systematic review and comprehensive meta-analysis

Background

HLA-G is associated with cancer cell escape. The 3'UTR polymorphism is involved in the regulation of membrane-bound HLA-G and soluble HLA-G proteins. The aim of our study was to assess the association of the HLA-G 14-bp insertion (I)/deletion (D) polymorphism with cancer susceptibility and its interaction with clinicopathological features and environmental factors.

Methods

A meta-analysis was performed to investigate the association between the HLA-G 14-bp I/D polymorphism and different types of cancers according to the Prisma guidelines.

Results

Thirty-nine publications that studied the 14-bp I/D polymorphism in cancers met our inclusion criteria. The findings of the meta-analysis showed a significant association between the 14-bp I/D polymorphism and cancer risk under the allelic contrast model D vs. I (OR = 1,112, 95 % CI = 1,009-1,227; P = 0,033) suggesting that the D allele was a risk factor for cancer susceptibility. Stratification by cancer type demonstrated a significant association of the 14-bp I/D polymorphism with breast cancer under the D vs. I contrast allele model (OR = 1,267, 95 % CI = 1,028-1,563; P = 0,027). No significant association was found for digestive, cervical, haematological and thyroid cancers. A comparison of groups stratified by ethnicity showed a significant association for Caucasians under the D vs. I model (OR = 1,147, 95 % CI = 1,002-1,313; P = 0,047); and for mixed ethnicities under the DD + DI vs. II (OR = 1,388, 95 % CI = 1,083-1,780; P = 0,010) and DI vs. II (OR = 1,402, 95 % CI = 1,077-1,824; P = 0,012) models. A comparison of cancer risks associated with the 14-bp I/D polymorphism according to geographic location revealed significant risks for the D allele and DD genotype in North Africa, the Middle East and South America. However, no significant susceptibility to cancer associated with the 14-bp I/D polymorphism was shown for Europe and North Asia. The findings of a meta-analysis of subgroups by disease stage showed a significant association in both early and advanced stages, with the 14-bp deletion variant being a risk factor. Similarly, a significant cancer risk was shown for the 14-bp deletion variant in both low- and high-grade cancers. Finally, the risk associated with the 14-bp I/D polymorphism was higher in cancers with concomitant viral infection with human papillomavirus (HPV), hepatitis B virus (HBV) or hepatitis C virus (HCV).

Conclusion

The findings of the overall meta-analysis showed a significant association between the HLA-G 14-bp I/D polymorphism and cancer susceptibility. The findings stratified analysis and subgroup comparisons showed that the 14-bp I/D deletion variant was associated with an increased risk of breast cancer. The HLA-G 14-bp I/D polymorphism may interact with individual and clinicopathological factors to alter cancer risk. These promising findings for cancer risk provide the basis for further studies that explore 14bp I/D polymorphism in cancer screening and immunotherapeutic approach.

HLA-G 14 bp Ins/Del (rs66554220) Variant Is Not Associated with Breast Cancer in Women from Western Mexico

HLA-G is a physiology and pathologic immunomodulator detrimentally related to cancer. Its gene is heavily transcriptionally and post-transcriptionally regulated by variants located in regulator regions like 3'UTR, being the most studied Ins/Del of 14-bp (rs66554220), which is known to influence the effects of endogen cell factors; nevertheless, the reports are discrepant and controversial. Herein, the relationship of the 14-bp Ins/Del variant (rs66554220) with breast cancer (BC) and its clinical characteristics were analyzed in 182 women with non-familial BC and 221 disease-free women as a reference group. Both groups from western Mexico and sex-age-matched (sm-RG). The rs66554220 variant was amplified by SSP-PCR and the fragments were visualized in polyacrylamide gel electrophoresis. The variant rs66554220 was not associated with BC in our population. However, we suggest the Ins allele as a possible risk factor for developing BC at clinical stage IV (OR = 3.05, 95% CI = 1.16-7.96, p = 0.01); nevertheless, given the small stratified sample size (n = 11, statistical power = 41%), this is inconclusive. In conclusion, the 14-bp Ins/Del (rs66554220) variant of HLA-G is not associated with BC in the Mexican population, but might be related to advanced breast tumors. Further studies are required.

HLA-G 5'URR regulatory polymorphisms are associated with the risk of developing gliomas

BACKGROUND

Human leukocyte antigen G (HLA-G) belongs to non-classical MHC class I molecules that is involved in the suppression of immune response. As HLA-G plays important role in the maintenance of fetal tolerance, its overexpression has been associated with tumor progression. For the regulation of HLA-G levels, genetic variants within the 5' upstream regulatory region (5'URR) are of crucial importance. Our study aimed to analyze the association between 16 HLA-G 5'URR variants, sHLA-G level and clinical variables in glioma patients.

METHODS

We investigated 59 patients with gliomas (mean age 54.70 ± 15.10 years) and 131 healthy controls (mean age 41.45 ± 9.75 years). Patient's blood was obtained on the day of surgical treatment. The HLA-G 5'URR polymorphisms were typed by direct sequencing and the plasma level of sHLA-G assessed by ELISA.

RESULTS

Haploblock within HLA-G 5'URR consisting of -762T, -716G, -689G, -666T, -633A, followed by -486C and -201A alleles were significantly more frequent in patients with gliomas than in the controls (p < 0.05). No correlation of HLA-G 5'URR variants with sHLA-G plasma level was found. Analysis of HLA-G 5'URR variants with main clinical variables in patients with grade IV gliomas revealed that haploblock carriers of -762CT, -716TG, -689AG, -666GT, -633GA, -486AC, -477GC, -201GA followed by -369AC carriers tend to have lower age at onset as compared to other genotype carriers (p = 0.04).

CONCLUSION

Our results suggest genetic association of HLA-G 5'URR variants with risk of developing gliomas and possible contribution of HLA-G to disease pathology.

3'UTR-HLA-G polymorphisms and circulating sHLA-G are associated with breast cancer: Evidence from a meta-analysis

BACKGROUND

Human leukocyte antigen-G (HLA-G) gene polymorphisms and circulating sHLA-G have often been linked to the risk of breast cancer (BC). However, the results remain controversial. To resolve this issue, we performed a meta-analysis of HLA-G gene polymorphisms and sHLA-G levels in BC.

METHODS

We performed a meta-analysis on the association of HLA-G 14-bp Insertion/Deletion (Ins/Del) and HLA-G +3142 C/G polymorphisms with BC as well as the relationship between sHLA-G and the disease outcome.

RESULTS

Pooled analysis showed a statistically significant association between the HLA-G 14-bp Ins/Del polymorphism and BC susceptibility for the overall population and for Caucasians. The Del allele and genotypes with at least one copy of the Del allele presented significant risks for BC. For HLA-G +3142 C/G polymorphism, the G allele significantly decreased the risk of BC for the overall population and for Caucasians, indicating that the G allele was a protective factor against BC and that the C allele was a significant risk factor for BC. The meta-analysis revealed a significantly increased level of sHLA-G patients with BC compared to the control group for the overall population, Caucasians and Asians.

CONCLUSION

The present meta-analysis showed a major association of both HLA-G 14-bp Ins/Del and +3142 C/G polymorphisms with BC susceptibility, suggesting Del and C variants as highly significant risk factors for BC. The present study also showed significantly higher sHLA-G levels in patients with BC compared to healthy controls. Our pooled results suggested a critical role of HLA-G in BC, thereby providing evidence to use HLA-G as a biomarker and a therapeutic tool.

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

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

Systematic Evaluation of HLA-G 3'Untranslated Region Variants in Locally Advanced, Non-Metastatic Breast Cancer Patients: UTR-1, 2 or UTR-4 are Predictors for Therapy and Disease Outcome

Despite major improvements in diagnostics and therapy in early as well as in locally advanced breast cancer (LABC), metastatic relapse occurs in about 20% of patients, often explained by early micro-metastatic spread into bone marrow by disseminated tumor cells (DTC). Although neoadjuvant chemotherapy (NACT) has been a successful tool to improve overall survival (OS), there is growing evidence that various environmental factors like the non-classical human leukocyte antigen-G (HLA-G) promotes cancer invasiveness and metastatic progression. HLA-G expression is associated with regulatory elements targeting certain single-nucleotide polymorphisms (SNP) in the HLA-G 3’ untranslated region (UTR), which arrange as haplotypes. Here, we systematically evaluated the impact of HLA-G 3’UTR polymorphisms on disease status, on the presence of DTC, on soluble HLA-G levels, and on therapy and disease outcome in non-metastatic LABC patients. Although haplotype frequencies were similar in patients (n = 142) and controls (n = 204), univariate analysis revealed that the UTR-7 haplotype was related to patients with low tumor burden, whereas UTR-4 was associated with tumor sizes >T1. Furthermore, UTR-4 was associated with the presence of DTC, but UTR-3 and UTR-7 were related to absence of DTC. Additionally, increased levels of soluble HLA-G molecules were found in patients carrying UTR-7. Regarding therapy and disease outcome, univariate and multivariate analysis highlighted UTR-1 or UTR-2 as a prognostic parameter indicative for a beneficial course of disease in terms of complete response towards NACT or progression-free survival (PFS). At variance, UTR-4 was an independent risk factor for a reduced OS besides already known parameters. Taken into account the most common HLA-G 3’UTR haplotypes (UTR-1–UTR-7, UTR-18), deduction of the UTR-1/2/4 haplotypes to specific SNPs revealed that the +3003C variant, unique for UTR-4, seemed to favor a detrimental disease outcome, while the +3187G and +3196G variants, unique for UTR-1 or UTR-2, were prognostic parameters for a beneficial course of disease. In conclusion, these data suggest that the HLA-G 3’UTR variants +3003C, +3187G, and +3196G are promising candidates for the prediction of therapy and disease outcome in LABC patients.

HLA-G 14bp Ins/Del Polymorphism in the 3'UTR Region and Acute Rejection in Kidney Transplant Recipients: An Updated Meta-Analysis

Background and Objectives: Acute kidney injury (AKI) affects the survival rate of kidney transplant organs and patients. Acute rejection (AR) due to AKI may lead to kidney transplantation failure. It is known that there is a relationship between human leukocyte antigen-G (HLA-G), which is involved in immune regulation, and AR in transplant patients. Moreover, 14-bp insertion/deletion polymorphism in the 3' untranslated region (UTR) region of the HLA-G gene is known to affect HLA-G expression. However, its relationship to AR is still controversial. The aim of this study was to investigate whether HLA-G 14-bp insertion/deletion polymorphism contributed to the development of AR in kidney transplant patients using a meta-analysis. Materials and Methods: To perform our meta-analysis, eligible studies about HLA-G 14-bp insertion/deletion polymorphism and AR were searched in electronic databases until 1 June 2021. Finally, a total of 336 patients with AR and 952 patients without AR in relation to kidney transplantation were analyzed from a total of nine studies. Results: In our results, the Del allele and Ins/Del+Del/Del and Del/Del genotypes significantly increased susceptibility of AR in Asian populations [odds ratio (OR) = 2.359, 95% confidence interval (CI) = 1.568-3.550, p = 3.8 × 10^-5; OR = 3.357, 95% CI = 1.769-6.370, p = 0.002; OR = 2.750, 95% CI = 1.354-5.587, p = 0.0052 in each model, respectively]. Conclusions: Evidence of the present results indicate that HLA-G 14-bp insertion/deletion polymorphism is associated with susceptibility to AR in the Asian population.

Association of the 3' untranslated region polymorphisms of HLA-G with susceptibility to chronic hepatitis C virus infection in the Chinese population

Hepatitis C virus (HCV) infection is a global health problem. Several previous studies have addressed the role of host single-nucleotide polymorphisms (SNPs) in HCV infection. SNPs in the regulatory region of the human leukocyte antigen G (HLA-G) gene play an important role in several diseases. The objective of this study is to determine the association of HLA-G 3'untranslated region (UTR) polymorphisms with the susceptibility to chronic hepatitis C infection in the Chinese population. HLA-G 3' UTR polymorphisms, which include 14-bp Ins/Del (rs371194629), +3003T/C (rs1707), +3010C/G (rs1710), +3027 A/C (rs17179101), +3035C/T (rs17179108), +3142 G/C (rs1063320), +3187 A/G (rs9380142) and + 3196C/G (rs1610696), were analyzed in 246 patients with chronic hepatitis C infection and 294 healthy individuals. The alleles, genotypes, and haplotypes were compared between chronic hepatitis C-infected subjects and controls using chi-square tests and logistic regression models. After a correction of multiple comparisons by the false discovery rate (FDR), the allele frequency of + 3196C, genotype frequencies of + 3187 AA and + 3196CC and frequency of the UTR-3 haplotype were significantly higher in the patients than in the control group (P < 0.05), whereas the frequencies of UTR-1 and UTR-2 haplotypes were significantly lower in the patients than in the control group (P < 0.05). After a correction of multiple comparisons by FDR, UTR-2 and UTR-3 maintained significant associations with chronic hepatitis C. This study indicates that HLA-G 3'UTR polymorphisms are associated with the susceptibility to chronic hepatitis C infection in the Chinese population. HLA-G 3'UTR may play an important role in risk modulation toward HCV infection.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

HLA-G Genotype/Expression/Disease Association Studies: Success, Hurdles, and Perspectives

The non-classical HLA-G is a well-known immune-modulatory molecule. In physiological condition, HLA-G surface expression is restricted to the maternal–fetal interface and to immune-privileged adult tissues, whereas soluble forms of HLA-G are detectable in various body fluids. HLA-G can be de novo expressed in pathological conditions including tumors, chronic infections, or after allogeneic transplantation. HLA-G exerts positive effects modulating innate and adaptive immune responses and promoting tolerance, or detrimental effects inducing immune escape mechanisms. HLA-G locus, in contrast to classical HLA class I gene, is highly polymorphic in the non-coding 3′ untranslated region (UTR) and in the 5′ upstream regulatory region (5′ URR). Variability in these regions influences HLA-G expression by modifying mRNA stability or allowing posttranscriptional regulation in the case of 3′ UTR or by sensing the microenvironment and responding to specific stimuli in the case of HLA-G promoter regions (5′ URR). The influence of genetic variations on the expression of HLA-G makes it an attractive biomarker to monitor disease predisposition and progression, or response to therapy. Here, we summarize the current knowledge, efforts, and obstacles to generate a general consensus on the correlation between HLA-G genetic variability, protein expression, and disease predisposition. Moreover, we discuss perspectives for future investigation on HLA-G genotype/expression in association with disease predisposition and progression.

HLA-G 14 bp In/Del and +3142 C/G genotypes are differentially expressed between patients with grade IV gliomas and controls

Aim: Human Leukocyte Antigen-G (HLA-G) is a non-classical class I molecule that is involved in maternal-fetal immunotolerance. In cancer, this molecule contributes to the tumor escape. The aim of this study was to evaluate the 14 bp In/Del and +3142 C > G polymorphisms of the HLA-G 3' UTR and its relation with plasma and tissue HLA-G expression in patients with grade IV (high-grade) and grade I/II (low-grade) gliomas and controls.Patients and methods: Peripheral blood and tumor biopsies were collected from 85 patients with gliomas and blood samples from 94 controls. Polymorphisms were analyzed from blood DNA. Soluble HLA-G (sHLA-G) was measured by ELISA in plasma of the subjects and the tissue expression by immunohistochemistry on patient's tissue.Results: Higher levels of sHLA-G were observed in grade IV gliomas patients than in controls (p < 0.0001). In grade IV patients, the heterozygous 14pb In/Del, +3142 C/G genotypes and Del/C*In/G haplotype were associated with higher sHLA-G levels (p < 0.0001) when compared with controls. GBM patients were stratified into high and low sHLA-G expression and an association was found between +3142 C allele and high sHLA-G plasmatic levels (p = 0.0095). Tissue HLA-G immunolabel was higher in high-grade than low-grade gliomas (p = 0.0033).Conclusion: This was the first study evaluating HLA-G 3' UTR polymorphisms and expression in patients with gliomas. The 14 bp In/Del and +3142 C/G genotypes and haplotypes showed high influence over sHLA-G expression, suggesting a heterozygous advantage in the tumor context and may contribute to a worse prognosis in glioma patients.

Association of HLA-G 3'UTR 14-bp Ins/Del polymorphism with breast cancer among South Indian women

AIM

Human leucocyte antigen-G (HLA-G) and tumour necrosis factor-alpha (TNF-α) are potent immune mediators implicated in the pathogenesis of breast cancer. The polymorphisms in the 3' untranslated region (3'UTR) of HLA-G and promoter region of TNF-α are well known to influence their expression levels and may consequently contribute to varied disease predisposition. Therefore, in the present study, we explored the effect of HLA-G 3'UTR (14-bp Ins/Del and +3142 C/G) and TNF-α promoter (-238 G/A and -308 G/A) polymorphisms on breast cancer risk among South Indian women.

METHODS

A total of 342 women (100 patients with breast cancer, 142 patients with benign breast disorder and 100 healthy women volunteers) were enrolled for this study. Genotyping of HLA-G and TNF-α polymorphisms were performed by direct PCR DNA amplification and amplification refractory mutation system PCR methods, respectively.

RESULTS

Significantly higher frequencies of HLA-G 14-bp Ins allele and Ins/+3142G haplotype were observed in patients with breast cancer than healthy controls (OR=1.56, P_c=0.036) and patients with benign breast disorder (OR=1.47, P_c=0.046). Similarly, subgroup analysis based on age at diagnosis (age≤50 years and >50 years) of breast cancer revealed higher frequencies of 14-bp Ins allele and Ins/+3142G haplotype in the patients of age >50 years than healthy controls (OR=1.77, P_c=0.03). Additionally, the extended haplotypes and multifactor dimensionality reduction analysis of the studied polymorphisms revealed significant contribution of HLA-G 14-bp Ins/Del polymorphism towards breast cancer risk.

CONCLUSION

The findings of the present study suggest that the HLA-G 14-bp Ins/Del polymorphism could influence breast cancer pathogenesis among South Indian women.

The Impact of HLA-G 3'UTR Polymorphisms in Breast Cancer in a Tunisian Population

Human leukocyte antigens G and E (HLA-G and HLA-E) are nonclassical major histocompatibility complex (MHC) class I molecules. These molecules play an important role in immune surveillance by inhibiting natural killer and cytotoxic T cells responsible for immune escape. The expression of HLA-G and HLA-E has been associated with several diseases including tumor. The main objective of the study is to evaluate the impact of three HLA-G 3'UTR potential polymorphisms: +3187 A > G (rs9380142), +3142 G > C (rs1063320), +2960 14-base pair (bp) Insertion/Deletion (Ins/Del) (rs66554220), and the HLA-E*01:01/01:03 A > G (rs1264457) polymorphism in Tunisian breast cancer population. A total of 355 patients and 381 controls were genotyping for HLA-G and HLA-E polymorphisms using a Taq Man assay. +3142 C allele and +3142 C/C genotype were significantly associated with increased risk of breast cancer (p = 0.00002; OR = 1.58; 95% CI = 27-1.97) (49% versus 35%; p = 0.0001; OR = 1.79; 95% CI = 1.32-2.44). In addition, Del allele and the homozygous state for Del/Del genotype confer a risk for breast cancer (52% versus 45%, p = 0.006; OR = 1.33, 95% CI = 1.08-1.64) (28% versus 22%, p = 0.039; OR = 1.43, 95% CI = 0.90-2.25). However, no statistical significant differences were reported for HLA-G + 3187 A > G and HLA-E variations and breast cancer in a Tunisian population. The found results indicate that HLA-G may play an important role in the breast cancer.

Genetic variation in the HLA-G 3'UTR 14-bp insertion/deletion and the associated cancer risk: evidence from 25 case-control studies

Human leucocyte antigen-G (HLA-G) plays an important role in the progression of human cancers. A growing number of published studies have investigated the correlation between the HLA-G 3' untranslated region (3'UTR) 14-bp insertion/deletion (Ins/Del) polymorphism and the associated cancer risk in different populations. However, results from previous studies are inconclusive and inconsistent for the different type of cancers. Therefore, we undertook a meta-analysis to assess the effects of the HLA-G 14-bp Ins/Del polymorphism on cancer risk. A systematic literature search was conducted in PubMed, Web of Science, CNKI, VIP, and Wanfang databases to obtain relevant studies up to 28 January 2019. The pooled odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were used. Twenty-five published case-control studies comprising 4981 cases and 6391 controls were included in the current meta-analysis. The results of the overall analysis revealed that the HLA-G 14-bp Ins/Ins genotype and Ins allele were associated with the total cancer risk in the homozygote comparison model (Ins/Ins vs. Del/Del: OR = 0.80, CI = 0.64-1.00; P=0.049) and the allelic comparison model (Ins vs. Del: OR = 0.89, CI = 0.81-0.99; P=0.035), with a protective role. Further subgroup analyses indicated that the HLA-G 14-bp Ins/Del polymorphism was associated with the risk of breast cancer and oesophageal cancer (EC), and significant risk of cancer was also observed in Mixed populations and population-based (PB). The results of our meta-analysis show that the HLA-G 14-bp Ins/Del polymorphism plays an important role in cancer risk, particularly in breast cancer and esophageal cancer in Mixed populations. Additional case-control studies with different types of cancer spanning different ethnicities are needed to extend the present findings.

Genetic association between HLA-G 14-bp polymorphism and diseases: A systematic review and meta-analysis

BACKGROUND

HLA-G is an immune checkpoint molecule. Since a differential molecule expression has been reported even for healthy individuals, many studies have focused on polymorphisms at HLA-G regulatory regions, particularly the 3' untranslated region (3'UTR). The presence/absence of a 14-bp sequence was the first polymorphism described and it is the most studied in association between HLA-G and disorders.

METHODS

In this study, we performed a systematic review and meta-analysis of all association studies published regarding the HLA-G 14-bp.

RESULTS

We verified association between 14-bp alleles and diseases in the following situations: (1) presence of 14-bp (insertion) conferred susceptibility to preeclampsia (child alleles evaluated) and systemic lupus erythematosus (OR = 1.42; 95%CI = 1.04-1.93; p = 0.026 and OR = 1.13; 95%CI = 1.01-1.27, p = 0.028); (2) 14-bp absence (deletion) was associated with increased risk to breast cancer (OR = 1.23; 95%CI = 1.06-1.43; p = 0.006) and human Cytomegalovirus infection (OR = 2.06; 95%CI = 1.60-2.64; p < 0.0001); and (3) a risk association was observed between the group of reproductive disorders and the 14-bp insertion (OR = 1.12; 95%CI = 1.01-1.24; p = 0.034).

CONCLUSIONS

Considering that others 14-bp associations were inconclusive and that other variation sites observed at HLA-G 3'UTR exhibit a proven role on post-transcriptional regulation of HLA-G expression, the complete 3'UTR segment should be analyzed in terms of disease susceptibility, instead of a single polymorphism.

Comparison of 3 Methodologies for Genotyping of Small Deletion and Insertion Polymorphisms

BACKGROUND

The quantification of genomic chimerism is increasingly recognized for its clinical significance after transplantation. Before the measurement of chimerism, accurate genotyping of genetic polymorphisms for informative alleles that can distinguish donor DNA from recipient DNA is essential. The ease of allelic discrimination of small deletion and insertion polymorphisms (DIPs) makes DIPs attractive markers to track chimerism. Current methodologies for the genotyping of DIPs are largely based on “open-tube” approaches. “Closed-tube” approaches involving no or minimal post-PCR handling are preferred. We compared 3 distinct methodologies to determine an optimal platform for DIP genotyping.

METHODS

Genomic DNA from 19 normal individuals was genotyped for 6 small biallelic DIPs using high-resolution melting analysis (HRMA), probe-free droplet digital PCR (ddPCR), and microfluidic electrophoresis of PCR products. For HRMA, 3 different platforms were compared.

RESULTS

Our newly developed probe-free ddPCR approach allowed the genotype of each DIP to be determined by fluorescence intensity based on amplicon size. Microfluidic electrophoresis also allowed genotypes to be determined by amplicon size. HRMA assays allowed the genotype of each DIP to be determined by melting profile. Genotyping results were concordant between the 3 methodologies. HRMA was the most readily performed methodology and was robust across 3 separate HRMA-capable platforms.

CONCLUSIONS

We demonstrated the effectiveness of probe-free ddPCR to accurately genotype small biallelic DIPs. Nevertheless, HRMA proved to be the optimal approach for genotyping small DIPs because closed-tube approaches are preferred owing to rapid and less laborious workflows and least risk of PCR contamination.

14-bp Insertion/Deletion Polymorphism of the HLA-G gene in Breast Cancer among Women from North Western Iran

BACKGROUND

The human leukocyte antigen-G (HLA-G) gene is highly expressed in cancer pathologies and is one strategy used by tumor cells to escape immune surveillance. A 14-bp insertion/deletion (InDel) polymorphism of the HLA-G gene has been suggested to be associated with HLA-G mRNA stability and the expression of HLA-G. The aim of present study was to assess any genetic association between this polymorphism and breast cancer among Iranian-Azeri women.

MATERIALS AND METHODS

In this study 227 women affected with breast cancer, in addition to 255 age-sex and ethnically matched healthy individuals as the control group, participated. Genotyping was performed using polymerase chain reaction and electrophoresis assays. The data were compiled according to the genotype and allele frequencies, compared using the Chi-square test. Statistical significance was set at P<0.05.

RESULTS

In this case-control study, no significant difference was found between the case and control groups at allelic and genotype levels, although there is a slightly higher allele frequency of HLA-G 14bp deletion in breast cancer affected group. However,when the stage I subgroup was compared with stage II plus stage III subgroup of affected breast cancer, a significant difference was seen with the 14 bp deletion allele frequency. The stage II-III subgroup patients had higher frequency of deletion allele (57.4% vs 45.8%) than stage I cases (χ2=4.16, p-value=0.041).

CONCLUSIONS

Our data support a possible action of HLA-G 14bp InDel polymorphism as a potential genetic risk factor for progression of breast cancer. This finding highlights the necessity of future studies of this gene to establish the exact role of HLA-G in progression steps of breast cancer.

HNRNPR Regulates the Expression of Classical and Nonclassical MHC Class I Proteins

MHC class I molecules, in addition to their role in specific activation of the CTL of adaptive immune system, function also as the main ligands for NK cell inhibitory receptors, which prevent NK cells from killing normal, healthy cells. MHC class I proteins are divided into classical and nonclassical proteins. The former group consists of hundreds of HLA-A, B, and C alleles, which are universally expressed, whereas several alleles of the latter group, such as HLA-G, manifest a restricted expression pattern. Despite the important role played by these molecules in innate and adaptive immune responses, their complex expression regulation is not fully known. In our study, we investigated the regulation processes controlling the expression of MHC class I molecules, with a particular focus on their 3' untranslated regions. We identified heterogeneous nuclear ribonucleoprotein R (HNRNPR) as an important positive regulator of classical and nonclassical MHC class I molecules. HNRNPR is a RNA-binding protein belonging to the heterogeneous nuclear ribonucleoprotein family, which has a known role in processing of precursor mRNA. We demonstrated that HNRNPR binds MHC class I mRNAs in their 3' untranslated regions and enhances their stability and consequently their expression. Furthermore, regulation by HNRNPR modulates the cytotoxic activity of NK cells. In conclusion, we show that HNRNPR acts as a general positive regulator of MHC class I expression.

HLA-G 14-bp Ins/Ins Genotype in Patients Harbouring Helicobacter pylori Infection: A Potential Risk Factor?

H. pylori is a potent pathogen due to its capacity to successfully evade host defence mechanisms. Despite inducing immune responses in infected individuals, sometimes these responses fail to clear the infection and the bacterium establishes a persistent infection leading to chronic inflammation. In this context, we hypothesized that human leucocyte antigen G (HLA-G), a non-classical major histocompatibility complex molecule that has the ability to regulate immune responses both in physiological and in pathological conditions, may play an important role in promoting tolerance and helping H. pylori to subvert host defence and consequently establish a chronic infection. Therefore, we evaluated the expression of HLA-G 14-bp Ins/Del polymorphism in patients harbouring H. pylori infection, as well as their relationship with histological and demographic variables, to gain a better understanding of the actual role of HLA-G and its genetic polymorphisms in bacterial infection. Sixty-eight patients with clinical symptoms suggestive of H. pylori infection were enrolled to assess HLA-G 14-bp Ins/Del polymorphism allele and genotype frequencies. After adjustment for covariates (age and gender), the odds of having the genotype Ins/Ins, compared to Del/Del, were 3.77 times greater among HP+ cases than among controls. These findings suggest that the 14-bp Ins/Ins genotype, already associated with inflammatory and autoimmune diseases as well as some viral and parasitic infections, could confer a greater risk of developing H. pylori infection.

Role of microRNAs on HLA-G expression in human tumors

The non-classical human leukocyte antigen G (HLA-G) known to protect the embryo from immune cell destruction leading to fetal maternal tolerance is often overexpressed in human tumors of distinct origin thereby leading to an escape from T and NK cell-mediated immune response. The molecular mechanisms controlling HLA-G expression are complex and involve deregulation at the transcriptional, epigenetic and posttranscriptional level. Using bioinformatics and high through put analyses a number of microRNAs (miRs) have been identified, which were able to bind to the 3' UTR of HLA-G with distinct efficacy. This caused by a downregulation of HLA-G surface expression, which was associated with an increased immune response thereby overcoming the HLA-G-mediated immune tolerance. Reduced expression of HLA-G-specific miRs was associated with tumor progression and metastases and appear to affect directly or indirectly tumor characteristics, such as cell proliferation, apoptosis and resistance to chemotherapy. Recently, an interaction between long non-coding RNAs, such as HOTAIR, and HLA-G-specific miRs has also been demonstrated. This review summarizes the control of HLA-G expression and function by microRNAs as well as its clinical significance.

Human leukocyte antigen-G polymorphisms influence the clinical outcome in diffuse large B-cell lymphoma

The role of HLA-G is extensively studied in cancer due to its inhibition of the immune response. Several polymorphisms in the HLA-G gene have been reported to significantly affect its expression. We, therefore, investigated whether functionally relevant HLA-G polymorphisms, HLA-G-725C/G/T, and HLA-G 14-base pair, have any influence on the susceptibility to diffuse large B-cell lymphoma (DLBCL) and its clinical course. The polymorphisms were genotyped in 207 previously untreated patients with DLBCL and 150 unrelated controls. A significant difference in genotype distribution of HLA-G polymorphic genotypes between the patients and controls was found. The frequencies of the HLA-G-725GG or the HLA-G-725GC genotype were lower, and those of the HLA-G ins/ins genotype were higher in the patients compared with the controls. Patients carrying the HLA-G-725CC genotype presented a higher probability of overall survival (OS) than subjects with other genotype combinations of HLA-G-725C/G/T (P = 0.003). The homozygous HLA-G del/del had a lower probability of OS than subjects carrying the HLA-G deletion/insertion (del/ins) or the HLA-G ins/ins genotype (P = 0.009). Two HLA-G genotype-based risk groups were defined according to the genotype distribution. The high-risk (HR) group presented a shorter OS than low-risk (LR) patients (P = 0.001). In a multivariate analysis adjusted for International Prognostic Index (IPI) factors, both the intermediate high/high IPI-risk group (P < 0.0001) and the HR genotype group (P = 0.004) independently increased the risk of death. This is the first study indicating an important role of HLA-G polymorphisms for the clinical course of DLBCL. The potential influence of HLA-G polymorphisms on the susceptibility to DLBCL thus deserves further study.

The Role of HLA-G Molecule and HLA-G Gene Polymorphisms in Tumors, Viral Hepatitis, and Parasitic Diseases

Considering that the non-classical HLA-G molecule has well-recognized tolerogenic properties, HLA-G expression is expected to be deleterious when present in tumor cells and in cells chronically infected by viruses, whereas HLA-G expression is expected to be advantageous in autoimmune disorders. The expression of HLA-G on tissue or peripheral blood cells, the levels of soluble HLA-G and polymorphic sites along the gene have been studied in several disorders. In this study, we revised the role of the molecule and polymorphic sites along the HLA-G gene in tumors, viral hepatitis, and parasitic disorders. Overall, several lines of evidence clearly show that the induction of HLA-G expression in tumors has been associated with worse disease outcome and disease spread. In addition, the few studies conducted on hepatitis and parasitic disorders indicate that HLA-G may contribute to disease pathogenesis. Few isolated polymorphic sites, primarily located at the coding or 3′ untranslated HLA-G region, have been evaluated in these disorders, and a complete HLA-G typing together with the study of gene regulatory elements may further help on the understanding of the influence of the genetic background on disease susceptibility.