Understanding cellular variation in fetal hemoglobin distribution

The National Institute of Diabetes and Digestive and Kidney Diseases awarded Versiti Blood Health, Inc. $1,409,516 on July 1, 2026, under the Diabetes, Digestive, and Kidney Diseases Extramural Research program (CFDA 93.847) to define how genetic and epigenetic regulation of γ-globin expression shapes fetal hemoglobin distribution and modifies disease severity in sickle cell disease.

The project uses single-cell transcriptomics, chromatin accessibility profiling, and genome editing to identify and functionally validate regulatory elements that control fetal hemoglobin distribution in individuals with naturally occurring β-globin locus deletions, including hereditary persistence of fetal hemoglobin and α-thalassemia. The work integrates single-cell RNA sequencing and ATAC-seq analysis in hydroxyurea-treated patients with sustained high fetal hemoglobin levels but divergent clinical outcomes, with the central hypothesis that red cell-intrinsic regulation of γ-globin determines fetal hemoglobin distribution and that variation in this regulation underlies clinical heterogeneity among patients with elevated fetal hemoglobin.

Performance occurs in Wauwatosa, Wisconsin. The period of performance runs from July 1, 2026, through April 30, 2031.

Abstract

Sickle cell disease (SCD) is a severe inherited blood disorder affecting over 100,000 individuals in the united states and millions globally. IT is caused by a missense variant in the -globin gene that leads to hemoglobin s (HBS) polymerization, red blood cell (RBC) sickling, hemolysis, and downstream complications including vaso-occlusive crises (vocs), stroke, and progressive organ damage. Fetal hemoglobin (HBF, ₂₂) inhibits HBS polymerization and is a well-established modifier of disease severity. Pharmacologic agents such as hydroxyurea (HU), and naturally occurring deletions in the -globin locus, such as those found in hereditary persistence of fetal hemoglobin (hpfh), increase HBF and reduce clinical complications. However, many patients remain at risk for complications despite achieving high total HBF levels. Emerging data indicate that the distribution of HBF across individual rbcs, whether uniform (pancellular) or uneven (heterocellular), is a stronger determinant of clinical benefit than total HBF alone. The molecular mechanisms that govern this distribution remain poorly defined. This project will define how genetic and epigenetic regulation of -globin expression shapes HBF distribution and modifies disease severity in SCD. The central hypothesis is that red cell-intrinsic regulation of -globin determines HBF distribution, and that variation in this regulation underlies persistent clinical heterogeneity among patients with elevated HBF. Aim 1 will use single-cell transcriptomics, chromatin accessibility profiling, and genome editing to identify and functionally validate regulatory elements that control HBF distribution in individuals with naturally occurring -globin locus deletions, including hpfh and a-thalassemia. Aim 2 will study HU-treated patients with sustained high HBF levels but divergent clinical outcomes. By integrating single-cell RNA-SEQ, atac-SEQ, whole genome sequencing, and clinical phenotyping from multicenter cohorts, this aim will identify cell-intrinsic regulators associated with differential clinical outcomes. Functional studies in patient-derived erythroid cells will test whether candidate variants and pathways alter HBF distribution. This work addresses a critical GAP in SCD management by identifying mechanisms of incomplete therapeutic response and biomarkers of residual risk. Findings will support precision HBF-inducing strategies and the rational development of combination therapies to reduce disease burden in children and adults with SCD.