Sickle cell disease is a major clinical problem in the US, France, the United Kingdom, Brazil, and in Africa, India and the Middle East. A recent study shows that the annual cost of medical care in the US for people who suffer from sickle cell disease exceeds $1.1 billion. Sickle hemoglobin (HbS) polymerization drives the pathophysiology of this disease. Fetal hemoglobin (HbF) is present throughout fetal development and is replaced by adult hemoglobin (HbA). A major therapeutic goal in sickle cell disease is to induce high HbF levels in sickle erythrocytes. We contend that the amount of HbF per F-cell (HbF/F-cell) and the distribution of concentrations of HbF/F-cells is a critical determinant of disease severity. Existing measurement of hemolysate HbF concentration or the number of F-cells in blood does not measure HbF/F-cell or the distribution of HbF/F- cell in a patient blood sample. This unmet need is critical because even patients with high HbF can have severe disease since their HbF is unevenly distributed among F-cells and many F-cells have insufficient HbF concentrations to inhibit HbS polymerization. We hypothesize that the proportion of F-cells that have enough HbF to thwart HbS polymerization is the most critical predictor of the likelihood of severe sickle cell disease. HbF/F-cell should be the phenotype studied in HbF induction therapeutics and would also be useful in developing risk scores that project likelihoods for disease severity. A clinical method for rapidly ascertaining HbF/F-cell is currently not available. As HbF concentrations among F-cells are highly variable and clinically relevant, the predictive value of HbF would be improved with an assay measuring the distribution of HbF concentrations within F-cells. Physicians would be able to provide better care using an HbF diagnostic as a standard method to assess which patients have higher risk, as well those patients with lower risk. Our goal in this application is to develop a prototype diagnostic test that will then be developed as laboratory developed test (LDTs) in a Clinical Laboratory Improvement Amendments (CLIA) laboratory in a subsequent Phase 2 SBIR study, based on the pilot data obtained in this study.
The specific aims of this proposal are to first develop, optimize and validate an HbF/F-cell diagnostic and then to evaluate the diagnostic in a pilot study of human subjects with sickle cell disease. The long-term goal is to develop a test based on a flow cytometry kit for HbF/F-cell profiling and a license for use of an online tool for disease risk determination that can be done in any hospital with flow cytometry and internet capability.
For this pilot study, our approach is to first develop, optimize and validate a fetal hemoglobin diagnostic and then to evaluate the diagnostic test in a pilot study of human subjects with sickle cell disease.
