Complement dysregulation during vaso-occlusive episodes can predict development of acute chest syndrome in pediatric patients with sickle cell disease Free

Introduction Vaso-occlusive episodes (VOE) and acute chest syndrome (ACS) remain the leading cause of hospitalizations and morbidity in children with sickle cell disease (SCD). In the absence of available targeted therapy, supportive care is the mainstay of treatment. Identifying those at highest risk for developing ACS, a significant morbid complication, is also limited. Complement dysregulation is implicated in hemolysis and organ damage in humans and mice with ACS (Chonat et al., STM 2025). However, studies have not evaluated changes in complement dysregulation during VOE prior to the development of ACS. We hypothesize that complement dysregulation is a key driver in the pathophysiology of VOE and ACS and can serve as a novel biomarker and therapeutic target.

Methods This single institution, prospective study enrolled SCD patients 0-21 years old who were admitted for VOE at the Children's Healthcare of Atlanta from 2018-2021. Blood samples were collected within 48 hours of admission (acute) and at clinic follow up (steady-state) ≥4 weeks later. Clinical history and hemolytic biomarkers were collected. Proximal (Bb, C4, C4a, C4d), common (C3, C3a), and terminal (C5, C5a, C5b-9) complement pathway levels were measured using commercial ELISA kits. Paired and unpaired non-parametric tests were used to compare markers of hemolysis and complement activation at acute and steady-state time points. The performance of biomarkers to predict the development of ACS was analyzed with receiver operating characteristic (ROC) curves and area under the curve (AUC). Logistic regression models were used to test the association between biomarkers and clinical outcomes. All statistical analyses utilized GraphPad Prism.

Results Seventy patients were enrolled accounting for 100 VOE and 69 steady-state episodes. In paired data samples, a significant decrease in mean hemoglobin (Hgb, n=60, p<0.0001) was seen between steady-state and acute, while there was an increase in lactate dehydrogenase (LDH, n=52, p=0.0222), C4d (n=30, median=0.20 vs. 0.29 mg/L, p=0.0093), Bb (n=30, median=1.35 vs.1.80 ug/mL, p<0.0001), C3a & C5a (n=30, p=0.0017 & p=0.0035), and sC5b-9 (n=30, p=0.0427). Patients who developed ACS had lower hemoglobin F (HbF) percentage (n=17, median 9 vs. 13%, p=0.0141) and higher white blood cell (WBC) (n=17, median 14.1 vs. 8.96 thou/uL, p<0.0001), LDH (n=18, p=0.0001), C4d (n=14, median 0.49 vs. 0.31 mg/L, p=0.0052), Bb (n=14, median 2.08 vs. 1.53 ug/mL, p=0.0200), C3a (n=14, p=0.0021), and C5a (n=14, p=0.0125) levels at the time of admission compared to no ACS. Complement levels, WBC, HbF, and LDH at admission demonstrated good discriminatory ability for predicting the development of ACS: WBC (AUC 0.82, p<0.0001), HbF (AUC 0.70, p=0.0151), LDH (AUC 0.80, p=0.0002), C4d (AUC 0.75, p=0.0061), Bb (AUC 0.71, p=0.0210), C3a (AUC=0.77, p=0.0027), and C5a (AUC 0.72, p=0.0135). Patients in the upper 75^th percentile of LDH values (n=17) had a higher odds of developing ACS compared to those with lower LDH values (n=51) [OR =7.68, 95% CI: 2.09-24.82, p=0.0011]. Patients on hydroxyurea (n=46) had significantly lower odds of developing ACS compared to those not on hydroxyurea (n=6) [OR = 0.07, 95% CI: 0.01 - 0.67, p=0.0112]. Patients who developed ACS (n=17) were also more likely to require oxygen support [OR=30.67, 95% CI: 3.11 -12.90, p<0.0001] or a red cell transfusion [OR=13.71, 95% CI: 3.85-52.80, p<0.0001] than patients who did not develop ACS (n=53).

ConclusionsSignificant activation of the complement pathway alongside increased hemolysis is evident at admission for VOE. Elevated levels of WBC, C4d, Bb, C3a, and C5a demonstrated strong discriminatory ability to predict development of ACS, while LDH in the upper 75^th percentile was strongly associated with increased odds of ACS. These findings underscore the potential utility of these biomarkers in risk stratification during admission for VOE. Development of ACS was associated with increased severity of illness including oxygen support and red blood cell transfusions, highlighting the need for improved risk stratification and therapeutic interventions. Our data suggests that complement activation markers, LDH, and WBC could serve as valuable predictors for ACS. More importantly, proximal complement inhibition emerges as a promising therapeutic strategy to prevent ACS in high-risk patients.