Cross-sectional analysis of adhesion in individuals with sickle cell disease using a standardized whole blood adhesion bioassay to VCAM-1

Sickle cell disease (SCD) is characterized by frequent and unpredictable vaso-occlusive episodes (VOEs) that lead to severe pain, organ damage, and early death. Lack of reliable biomarkers that objectively define VOEs remains a critical barrier to improving the care for SCD patients. VOEs result from a complex interplay of cell-cell interactions that promote micro-vascular occlusion. Earlier studies demonstrated that sickle erythrocytes are more adherent than non-sickle erythrocytes and established a direct link between adhesion and frequency of VOEs. We developed a standardized, flow-based adhesion bioassay to assess the adhesive properties of SCD blood samples. The current study provides a cross-sectional analysis of steady state adhesion in SCD patients presenting at monthly out-patient hematology visits. Steady state adhesion varied from patient-to-patient. Adhesion positively correlated with reticulocyte percent and WBC count although there was no significant relationship between adhesion and platelets or hemoglobin in this study. Additionally, steady state adhesion indices were significantly lower in SCD subjects receiving hydroxyurea therapy when compared to the untreated group. The well-plate based microfluidic flow adhesion bioassay described in this report may provide a platform to identify SCD subjects with severe disease phenotypes, predict impending VOEs, and monitor response to current and developing therapies.