Lack of association between human leukocyte antigen-E alleles and nasopharyngeal carcinoma in Tunisians

Dimorphism of HLA-E and its Disease Association

HLA-E is a nonclassical member of the major histocompatibility complex class I gene locus. HLA-E protein shares a high level of homology with MHC Ia classical proteins: it has similar tertiary structure, associates with β2-microglobulin, and is able to present peptides to cytotoxic lymphocytes. The main function of HLA-E under normal conditions is to present peptides derived from the leader sequences of classical HLA class I proteins, thus serving for monitoring of expression of these molecules performed by cytotoxic lymphocytes. However, opposite to multiallelic classical MHC I genes, HLA-E in fact has only two alleles—HLA-E*01:01 and HLA-E*01:03—which differ by one nonsynonymous amino acid substitution at position 107, resulting in an arginine in HLA-E*01:01 (HLA-E^R) and glycine in HLA-E*01:03 (HLA-E^G). In contrast to HLA-E^R,HLA-E^G has higher affinity to peptide, higher surface expression, and higher thermal stability of the corresponding protein, and it is more ancient than HLA-E^R, though both alleles are presented in human populations in nearly equal frequencies. In the current review, we aimed to uncover the reason of the expansion of the younger allele, HLA-E^R, by analysis of associations of both HLA-E alleles with a number of diseases, including viral and bacterial infections, cancer, and autoimmune disorders.

Are HLA-E*0103 alleles predictive markers for nasopharyngeal cancer risk?

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a particular entity of head neck cancer, tightly related to Epstein-Barr virus infection and thus to HLA genes. In this study, we aimed to analyze HLA-E polymorphism in NPC advent and prognosis. 130 unrelated patients with CNP and 180 unrelated and healthy controls were included in our study. HLA-E genotyping was performed by PCR/RFLP method; SPSS (13.0) was used for statistical analysis, and survival curbs were established with the "Kaplan-Meier" method (Log Rank<0.05).

RESULTS

We found a significant difference within HLA-E*103 variants between patients and controls: E*1031 and E*1032 were associated with CNP (OR=1.613, p=0.013 and OR=1.0809, p=0.055), and E*1033 with controls (OR=0.254, p<10(-4)).

CONCLUSION

Our study reveals that HLA-E polymorphism is associated with nasopharyngeal cancer. HLA-E expression studies could be used to understand the implication of E*103 variants.

HLA Allele E*01:01 Is Associated with a Reduced Risk of EBV-Related Classical Hodgkin Lymphoma Independently of HLA-A*01/*02

BACKGROUND

An inefficient immune response against Epstein-Barr virus (EBV) infection is related to the pathogenesis of a subgroup of classical Hodgkin lymphomas (cHL). Some EBV immune-evasion mechanisms target HLA presentation, including the non-classical HLA-E molecule. HLA-E can be recognized by T cells via the TCR, and it also regulates natural killer (NK) cell signaling through the inhibitory CD94/NKG2A receptor. Some evidences indicate that EBV-infected B-cells promote the proliferation of NK subsets bearing CD94/NKG2A, suggesting a relevant function of these cells in EBV control. Variations in CD94/NKG2A-HLA-E interactions could affect NK cell-mediated immunity and, consequently, play a role in EBV-driven transformation and lymphomagenesis. The two most common HLA-E alleles, E*01:01 and E*01:03, differ by a single amino acid change that modifies the molecule function. We hypothesized that the functional differences in these variants might participate in the pathogenicity of EBV.

AIM

We studied two series of cHL patients, both with EBV-positive and-negative cases, and a cohort of unrelated controls, to assess the impact of HLA-E variants on EBV-related cHL susceptibility.

RESULTS

We found that the genotypes with at least one copy of E*01:01 (i.e., E*01:01 homozygous and heterozygous) were underrepresented among cHL patients from both series compared to controls (72.6% and 71.6% vs 83%, p = 0.001). After stratification by EBV status, we found low rates of E*01:01-carriers mainly among EBV-positive cases (67.6%). These reduced frequencies are seen independently of other factors such as age, gender, HLA-A*01 and HLA-A*02, HLA alleles positively and negatively associated with the disease (adjusted OR = 0.4, p = 0.001). Furthermore, alleles from both HLA loci exert a cumulative effect on EBV-associated cHL susceptibility.

CONCLUSIONS

These results indicate that E*01:01 is a novel protective genetic factor in EBV-associated cHL and support a role for HLA-E recognition on the control of EBV infection and lymphomagenesis.

NKG2C copy number variations in five distinct populations in mainland China and susceptibility to nasopharyngeal carcinoma (NPC)

In this study, copy number variation (CNV) of NKG2C gene was investigated in 1129 normal, unrelated individuals representing two southern Chinese Han populations (Hunan Han and Guangdong Han), two northern Chinese populations (Inner Mongolia Han and Inner Mongolia Mongol) and one southeastern Chinese Han population (Fujian Han) using polymerase chain reaction-sequence-specific priming (PCR-SSP) method. CNV of NKG2C gene did not vary significantly among the five Chinese populations, with NKG2C gene deletion showing a frequency ranging from 0.2031 to 0.2688. Compared with worldwide ethnic groups, very significant difference was observed between the five Chinese populations and the Mexican mestizos (all Pcorrected=0.0025), and between the Fujian Han population and the German population (Pcorrected=0.005). We further examined CNV of NKG2C and HLA-E allelic distribution in 653 patients afflicted with nasopharyngeal carcinoma (NPC) in Hunan province. Neither CNV of NKG2C nor HLA-E was associated with NPC. There was a trend of reduced NPC risk in individuals who were homozygous for both HLA-E(∗)01:03 and NKG2C deletion (0.46% vs. 2.51%, P=0.0076, Pcorrected=0.0684, OR (95% CI)=0.1794 (0.0473-0.6809)). Taken together, our results suggest that NKG2C deletion and HLA-E signalling pathway does not play a major role in determining genetic susceptibility to NPC.

Clinical and immunological significance of HLA-E in stem cell transplantation and cancer

Human leukocyte antigen-E (HLA-E) is a nonclassical HLA class I molecule that canonically binds peptides derived from the leader sequence of classical HLA class I. HLA-E can also bind peptides from stress protein [e.g. heat shock protein 60 (Hsp60)] and pathogens, illustrating the importance of HLA-E for anti-viral and anti-tumor immunity. Like classical HLA class I molecules, HLA-E is ubiquitously expressed, however, it is characterized by only a very limited sequence variability and two dominant protein forms have been described (HLA-E*01:01 and HLA-E*01:03). HLA-E influences both the innate and the adaptive arms of the immune system by the engagement of inhibitory (e.g. NKG2A) and activating receptors [e.g. αβ T cell receptor (αβTCR) or NKG2C] on NK cells and CD8 T cells. The effects of HLA-E on the cellular immune response are therefore complex and not completely understood yet. Here, we aim to provide an overview of the immunological and clinical relevance of HLA-E and HLA-E polymorphism in stem cell transplantation and in cancer. We review novel insights in the mechanism via which HLA-E expression levels are controlled and how the cellular immune response in transplantation and cancer is influenced by HLA-E.

Genetic predisposition factors and nasopharyngeal carcinoma risk: a review of epidemiological association studies, 2000-2011: Rosetta Stone for NPC: genetics, viral infection, and other environmental factors

While infection with Epstein-Barr virus (EBV) is known to be an essential risk factor for the development of nasopharyngeal carcinoma (NPC), other co-factors including genetic factors are thought to play an important role. In this review, we summarize association studies conducted over the past decade to evaluate the role of genetic polymorphisms in NPC development. A review of the literature identified close to 100 studies, including 3 genome-wide association studies (GWAS), since 2000 that evaluated genetic polymorphisms and NPC risk in at least 100 NPC cases and 100 controls. Consistent evidence for associations were reported for a handful of genes, including immune-related HLA Class I genes, DNA repair gene RAD51L1, cell cycle control genes MDM2 and TP53, and cell adhesion/migration gene MMP2. However, for most of the genes evaluated, there was no effort to replicate findings and studies were largely modest in size, typically consisting of no more than a few hundred cases and controls. The small size of most studies, and the lack of attempts at replication have limited progress in understanding the genetics of NPC. Moving forward, if we are to advance our understanding of genetic factors involved in the development of NPC, and of the impact of gene-gene and gene-environment interations in the development of this disease, consortial efforts that pool across multiple, well-designed and coordinated efforts will most likely be required.