Real-world Assessment of Red Blood Cell (RBC) Health Biomarkers in Sickle Cell Disease
Authors: White Jennell , Dingle Ryan , Bellemare Kerry , Hines Patrick C 
Published: June 2024

Abstract

Presentation Date: 6/9/2024
Presentation Start Time: 3:30:00 PM

Background
Sickle cell disease (SCD) is a rare, mono-genetic disease that prevents hemoglobin (Hb) and red blood cells (RBCs) from adequately delivering oxygen throughout the body. Although transfusion and hydroxyurea have historically been the standard of care, newly approved SCD-modifying and investigational therapies ultimately improve the health of circulating RBCs by increased affinity of Hb for oxygen, direct inhibition of p-selectin-mediated adhesion, reduction in RBC oxidative stress, and induction of fetal hemoglobin. Biomarkers to assess RBC health are poorly validated and not routinely available for SCD management thus, frequent and unpredictable vaso-occlusive episodes (VOEs) remain the standard clinical endpoints for clinical trials and patient care. We developed proprietary, adhesion assays as measurable targets of RBC health based on decades of data demonstrating RBC adhesion promotes VOEs, correlates with VOE frequency, and decreases alongside VOEs in response to therapy. Our RBC health biomarkers are available for clinicians to monitor patient response to therapy, identify severe disease phenotypes, and predict impending vaso-occlusive episodes (VOEs). We are the 1st to offer flow-based adhesion bioassays in a “real-world” clinical setting. The objective of this study is to provide an update on our real-world assessment of RBC health biomarkers in patients living with SCD.

Methods
Blood samples were received from 10 US clinics between March 2018 and February 2024. Biomarkers were ordered as standard clinical send-out (CSO) labs using unique Proprietary Laboratory Analysis (PLA) codes, including mechanical fragility (MFI3min & MFI10min 0123U) and, flow adhesion of whole blood to VCAM (FA-WB-VCAM; 0121U) and p-selectin (FA-WB-PSEL; 0122U). Samples were drawn in sodium citrate vacutainers and shipped overnight to our central lab in Detroit, MI. Specialized shipping containers were validated to maintain internal temperature between 2-8oC for 72 hrs. CSO lab values were exported from our laboratory management system (Ignite Medical Technologies) following an IRB-approved waiver of informed consent permitting access to patient information: clinical labs, VOE-related ER visits and hospitalizations, confirmed SCD-modifying therapy start/stop dates, pain and fatigue scores, and standard-of-care labs.

Results
A total of 19,629 (6543 clinical samples X 3 tests) individual tests were performed during the analysis period on 6543 individual clinical blood samples from 897 unique patients (female=506; male=391). These individuals were represented across the following age ranges: 0-9yrs (n = 298), 10-19yrs (n = 271), 20-29yrs (n = 141), 30-39yrs (n = 100), 40-49yrs (n = 49), and 50-59yrs (n = 26), 60-69yrs (n = 7), 70-79yrs (n = 4), and 80-89yrs (n = 1). Indications for testing included acute crisis (2841), baseline (1005), monitor therapy (1846), start therapy (100), and not specified (735). The number of blood samples tested in patients receiving SCD-modifying therapies includes the following: hydroxyurea (n = 3020), adakveo (n = 1240), voxelotor (n = 259), and endari (n = 289). Critical values were reported for 28.2% of all CSO labs received (5544 of 19629 samples): FA-WB-VCAM (1689), FA-WB-PSEL (2576), MFI3min (546), and MFI10min (733).

Conclusions
This report validates that careful coordination with our clinical send-out sites can facilitate successful sample acquisition, shipping, and processing of FA-WB-VCAM, FA-WB-Psel, and MF testing in a central lab setting. Most (50.1%) testing was indicated to monitor patients on therapy and a 132% increase since our last report (from 770 to 1846 samples) compared to a 24% increase in testing to assess RBC health at baseline or during acute crisis. This is likely due to the recent surge in approved SCD-modifying therapies in the last 6 years. We have generated the largest dataset of flow-based adhesion and membrane stability testing in clinical blood samples and will continue to analyze this data to assess the clinical utility of RBC health functional biomarkers in SCD. We recently reported a cellular level response to Adakveo (p-selectin inhibitor) in SCD patients pre- and post-treatment using FA-WB-PSEL. Additionally, FA-WB-PSEL was significantly lower post-treatment and, pre-treatment levels correlated with biomarker response to real-world Adakveo therapy. In a more recent report, we further validated that baseline FA-WB-VCAM identifies severe SCD phenotypes in a “real world” clinical setting and, SCD patients with severe adhesion phenotypes are associated with increased healthcare utilization. Multiple investigator-led collaborations are underway to leverage access to our population-scale RBC health database to gain more insight into post-market SCD-modifying therapies in the “real world”, identification of severe disease phenotypes, risk-stratification of impending VOEs, and evaluation of the baseline vs. acute crises state.