Transcranial Doppler Screening of Children with Sickle Cell Disease for a Large, Multinational Interventional Study: Experience from the Phase 3 HOPE-Kids 2 Trial Investigating the Effect of Voxelotor Treatment on Transcranial Doppler Flow Velocity

Introduction: Transcranial Doppler (TCD) ultrasound is an effective screening tool for identifying children with sickle cell disease (SCD) who are at high risk of stroke. Implementing TCD screening, along with appropriate therapies, for the purpose of primary stroke prevention in resource-constrained settings remains challenging. HOPE-KIDS 2 (NCT04218084) is an ongoing, phase 3, multicenter, double-blind, placebo-controlled trial of voxelotor in children with SCD and elevated arterial cerebral blood flow (measured by time-averaged maximum of the mean velocity [TAMMV]). Our aim is to describe the findings from successful implementation of a standardized TCD screening protocol that was conducted in a multinational setting.

Methods: The purpose of HOPE-KIDS 2 is to evaluate the effect of voxelotor treatment on reducing the risk of stroke in participants aged 2 to <15 years with SCD who have conditional TAMMV (170 to <200 cm/s) at baseline. Children aged 2 to <15 years with SCD (HbSS/HbSβ⁰) were screened after local sonographers were trained and certified on standardized TCD examination protocol, using the same model of Multi-Dop T digital machine (Compumedics DWL, Germany). TCD assessments were sent for central quality review and interpretation by 2 independent reviewers. STOP criteria were used to classify stroke risk: normal, <170 cm/s; conditional, 170 to <200 cm/s; or abnormal, ≥200 cm/s. Patient baseline characteristics, including clinical measurements of markers of anemia and hemolysis, were measured during study screening. The reasons for patient screen failure were summarized.

Results: Between Nov 2020 and Feb 2023, 708 participants consented at 29 sites in Nigeria (n=250; 5 sites), Kenya (n=241; 4 sites), Egypt (n=145; 4 sites), Ghana (n=28; 2 sites), the US (n=17; 8 sites), Italy (n=9; 3 sites), Oman (n=9; 1 site), Saudi Arabia (n=8; 1 site), and the UK (n=1; 1 site). Of these patients, 92.1% (652/708) completed TCD screening examinations (mean [SD] age 7.6 [3.24] years; range 2.0-14.0 years; 50.8% male; 23.0% receiving hydroxyurea). Of the patients who completed TCD screening, the mean (SD) TAMMV was 163.0 (31.26) cm/s, and 47.1% (307/652) had conditional TCD at baseline (29.0% low conditional, 18.1% high conditional). The main reason for screen failure was index TAMMV outside of conditional range (abnormal, n=39 [6.0%]; normal, n=306 [46.9%]). Elevated TAMMV on screening TCD was more common in younger children (2 to ≤8 years vs >8 to <15 years); patients aged 2-8 years comprised 66.8% and 82.1% of the conditional and abnormal TCD categories, respectively. There were 39 assessments that required adjudication, but only 9 were deemed unreadable. Of all patients screened, 36.2% (236/652) fulfilled eligibility criteria for randomization; the characteristics at screening of these patients are summarized (Table). The mean (SD) Hb level and TAMMV at screening for randomly assigned patients was 7.7 (1.06) g/dL and 182.7 (7.53) cm/s, respectively.

Conclusions: Clinical sites for the HOPE-KIDS 2 study successfully implemented a standardized, local TCD screening protocol supported by central quality review. For a large interventional trial aimed at reducing the risk of stroke in children with SCD, African and Middle Eastern sites presented relatively few limitations with respect to participant screening.