Omic Approaches to Factor VIII Inhibitor Development in Hemophilia Patients of Mexican Descent

PROJECT SUMMARY/ABSTRACT Bleeding in Hemophilia A (HA) is currently prevented by regular infusions of therapeutic factor VIII (FVIII) proteins (tFVIIIs). Unfortunately, ~30% of all severe HA patients (HAPs) develop antibodies called FVIII inhibitors (FEIs) that neutralize tFVIIIs and greatly increase morbidity & mortality. FEIs develop significantly more often in HAPs

with Mexican ancestry (MA) vs. non-Hispanic white (NHW) ancestry. This research seeks to identify genetic and environmental variables underlying the high incidence of FEIs in HAPs of MA by applying novel omic approaches in a powerful systematic immunoepidemiologic study of the immunogenicity of tFVIIIs. We will leverage a unique

resource, the My Life, Our Future (MLOF) repository, which has ~400 such subjects already enrolled in our study. We have four main aims. Aim 1: To enroll and extensively characterize a cohort of 200 severe HAPs with MA. We will recruit 200 severe HAPs (including 30 sib pairs) in the US and Mexico. Relevant clinical data and

blood samples will be collected to assess FEI risk. We will use the (i) WGS and mRNA-Seq data from these 200 new individuals plus the ~400 subjects of MA in the MLOF project (N=600) and (ii) functional CD4 T-cell data from all 200 new subjects. We will assess intracellular (i) CRM status (i.e., presence or absence of FVIII antigen)

in all 200 new subjects, as this variable underlies the contribution of F8 mutation type to FEI risk. Aim 2: To elucidate the genetic basis of FEI risk in MA severe HAPs using trans-omic endophenotypes. Using a novel statistical genetics approach employing both close and distant relatedness in the overall sample of ~600

MA severe HAPs, we will identify endophenotypes genetically correlated with FEI risk from novel phenotypic measures immunologically related to FEI development. The best endophenotypes for FEI risk will be genetically characterized using both quantitative genetic methods and variant-specific association analyses. Aim 3: To

detect and characterize environmental effects on FEI risk. Using a novel statistical genetic approach to maximize systematic environmental signals influencing FEI risk, we will search for environmental traits reflected in high-dimensional transcriptomic biomarkers that are correlated with FEI development. Aim 4: To perform a

case/control peptidomic analysis of FEI risk. We will select a subset of 40 HAPs as 20 FEI discordant sib pairs (one brother has a FEI and the other does not) and recruit their carrier mothers. We will characterize each subject’s tFVIII peptidome, i.e., the HLA-class-II (HLAII)-bound collection of tFVIII-derived-peptides (tFVIII:dPs)

that are presented to their CD4 T-cells. We will then identify the “culprit tFVIII:dP” and “offending HLAII allele” (OHA), which are most correlated with FEI development in the proband of each sib pair. Finally, we will evaluate the relevance of our findings using: 1) CRISPR/Cas9 to knockout (ko) specific OHAs in their B-lymphoblastoid

cells (BLCs) in vitro; and 2) their ko BLCs for functional T-cell studies. As tFVIIIs are more immunogenic in HAPs with MA, this study is likely to identify new determinants of FEI risk (both genetic & non-genetic) which will assist the development of new (i) diagnostics that are more accurate, (ii) therapeutics with improved safety and efficacy,

and (iii) management strategies that reduce race- and ethnicity-based disparities in health outcomes.