Modulation of Neutrophil Function by Red Cell Exchange in SCD Patients

/Abstract Activated and hyper-reactive neutrophils play a significant role in sickle cell disease (SCD). Recent evidence suggests that abnormally reactive neutrophils contribute to many of the thromboinflammatory complications of SCD, including acute chest syndrome and stroke. To prevent these complications or to treat acute events, many patients with SCD undergo a procedure called red cell exchange (RCE). RCE is an automated procedure which removes the patient’s endogenous red cells containing abnormal hemoglobin S (HbS) and infuses healthy donor red cells containing HbA. RCE is standard of care in both the inpatient and outpatient setting, as achievement and/or maintenance of HbS < 20-30% has been shown to reduce the otherwise high incidence of recurrent stroke and also leads to resolution of acute chest syndrome. However, whether RCE affects neutrophil activation and hyper-reactivity, thereby contributing to its beneficial effect on SCD complications, is unknown. To answer this question, as shown in preliminary data, we have begun to enroll a cohort of patients with SCD who undergo chronic RCE in the outpatient setting. Our preliminary data support the hypothesis that RCE reduces neutrophil hyper-reactivity, resulting in significantly attenuated degranulation responses to a range of agonists, including bacterial ligands. Furthermore, we show that these changes in neutrophil reactivity may be due to the presence/absence of circulating HbA/HbS. Based on the preliminary data presented in this application, we will test the hypothesis that RCE, and the replacement of abnormal HbS red cells with normal HbA red cells, modulates neutrophil reactivity and function. In Aim 1, we will comprehensively determine the effect of RCE on neutrophil function and phenotype and establish the time course of changes in neutrophil function. As well, we will perform a pilot study examining neutrophil function pre- and post-RCE in patients hospitalized with acute chest syndrome to determine whether our findings are applicable during an acute inflammatory event. In Aim 2, we will establish the multiple mechanisms whereby RCE modulates neutrophil reactivity. We will investigate 3 major pathways by which RCE may be modulating neutrophil function. Using artificially created admixtures of HbA and HbS red cells as well as admixtures obtained from SCD patients pre/post RCE, we will examine interactions between (1) neutrophil Siglec-9 and SS RBC glycophorin A, (2) neutrophils and phosphatidylserine exposed on SS RBCs, and (3) neutrophils and SS RBC adhesion molecules. As well, we will establish the impact of RCE on thromboinflammatory activity including heterotypic aggregate formation and markers of endothelial damage. Together, these studies build on our novel observation that RCE modulates neutrophil function. The overall goal of this proposal is to understand the effect of transfusion on neutrophil activation and to determine if inhibition of neutrophil reactivity can be used as a functional endpoint to establish personalized therapeutic targets for SCD patients. Findings from this proposal will guide future studies to identify functional biomarkers for high risk patients and will provide additional biological insight into the emerging role of neutrophils in SCD. Project Number: 1R21AI182883-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Grace Lee | Institution: DUKE UNIVERSITY, DURHAM, NC | Award Amount: $444,125 | Activity Code: R21 | Study Section: Hemostasis, Thrombosis, Blood Cells and Transfusion Study Section[HTBT] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R21AI18288301A1