Immunogenetics of factor VIII inhibitor development

Abstract

Objective: The purpose of our study is to investigate the hypothesis that polymorphisms in immunoregulatory genes and/or the factor VIII gene are partly responsible for recognition of therapeutic factor VIII as ‘foreign’, thereby provoking inhibitor antibodies. As a critical first step in our study we have set out to determine the minimal number of single nucleotide polymorphisms (SNPs) in immunoregulatory genes and the factor VIII gene that define the relevant DNA haplotypes seen in the Caucasian population (CEU) as shown in the HapMap project.Methods: We searched the CEU dataset in the HapMap genetic database (release 23a, March 8, 2008) as a source for SNPs with potential to define haplotypes ‘tag SNPs’ in the genes for IL1‐beta, IL4, IL10, IL13, interferon gamma, TNF‐alpha, TGF‐beta, zinc alpha‐2 glycoprotein I, and the coagulation factor VIII gene. These genes were selected based on their central role in regulation of the immune response, previously published correlations with factor VIII inhibitor risk, or results of studies of factor VIII immunogenicity in animals. Using the Haploview programme we surveyed SNPs in each gene, plus approximately 20 kb of DNA 5′ and 3′ to each gene to assess potential regulatory elements that might influence gene expression. Tag SNPs were picked for each gene at various levels of coverage, based on correlation coefficients (r2) of >0.8, >0.9, and =1.0.Summary: Our analysis indicates that the total number of tag SNPs required to study the nine genes of interest, with r2 values of > 0.8, > 0.9, or = 1.0, is on the order of 96, 138 and 146, respectively. Thus, a study of these proposed candidate genes is feasible with currently available SNP ascertainment based on multiplex PCR amplification/extension and MALDI‐TOF analysis.Conclusions: With approximately 150 SNPs (at r2 = 1.0) we will be able to determine association between factor VIII inhibitor development and any of seven immunoregulatory genes and two plasma proteins, including the coagulation factor VIII gene. We have extracted genomic DNA from peripheral blood leukocytes obtained from >900 caucasian haemophilia A patients who participated in the Multicenter Haemophilia Cohort Studies I & II, and are beginning to ascertain these SNPs for their association with risk for development of inhibitors to factor VIII in haemophilia A patients.