The role of HLA variation in lymphoma aetiology and survival.

ABSTRACT

Epidemiologic and laboratory evidence has consistently supported a strong inflammatory and immune component for lymphoma aetiology. These studies have consistently implicated variation in the immune gene, human leucocyte antigen (HLA), to be associated with lymphoma risk. In this review, we summarize the historical and recent evidence of HLA in both lymphoma aetiology and survival. The recent momentum in uncovering HLA associations has been propelled by the conduct of genome-wide association studies (GWAS), which has permitted the evaluation of imputed HLA alleles in much larger sample sizes than historically feasible with allelotyping studies. Based on the culmination of smaller HLA typing studies and larger GWAS, we now recognize several HLA associations with Hodgkin (HL) and non-Hodgkin lymphomas (NHLs) and their subtypes. Although other genetic variants have also been implicated with lymphoma risk, it is notable that HLA associations have been reported in every NHL and HL subtype evaluated to date. Both HLA class I and class II alleles have been linked with NHL and HL risk. It is notable that the associations identified are largely specific to each lymphoma subtype. However, pleiotropic HLA associations have also been observed. For example, rs10484561, which is in linkage disequilibrium with HLA-DRB1*0101˜DQA1*0101˜DQB1*0501, has been implicated in increased FL and DLBCL risk. Opposing HLA associations across subtypes have also been reported, such as for HLA-A*0101 which is associated with increased risk of EBV-positive cHL but decreased risk of EBV-negative cHL and chronic lymphocytic leukaemia/small cell lymphoma. Due to extensive linkage disequilibrium and allele/haplotypic variation across race/ethnicities, identification of causal alleles/haplotypes remains challenging. Follow-up functional studies are needed to identify the specific immunological pathways responsible in the multifactorial aetiology of HL and NHL. Correlative studies linking HLA alleles with known molecular subtypes and HLA expression in the tumours are also needed. Finally, additional association studies investigating HLA diversity and lymphoma survival are also required to replicate initial associations reported to date.