Helping Underdeveloped Lungs with Cells (HULC)-2 Mesenchymal Stromal Cells in extreme preterm infants at risk of developing Bronchopulmonary Dysplasia. A Phase 2 Multi-Centre Double Blind Randomized Controlled Trial Study Protocol.

IntroductionBronchopulmonary dysplasia (BPD) remains a major complication among extremely low gestational age (ELGA) infants, with long-term respiratory and neurodevelopmental consequences. Despite advances in neonatal care, effective therapies to prevent BPD are lacking. Mesenchymal stromal cells (MSC), particularly those derived from umbilical cord (UC-MSC), offer promise due to their pleiotropic effects. Preclinical and early-phase clinical studies have demonstrated safety and potential efficacy of MSC in neonatal lung injury. The HULC-2 trial aims to evaluate whether multiple intravenous doses of human allogenic UC-MSC can reduce mechanical ventilation duration and improve the respiratory outcome in ELGA infants at high risk of developing BPD. Methods and AnalysisHULC-2 is a multicenter, double-blind, randomized controlled Phase II trial conducted in Canadian Neonatal Intensive Care Units. ELGA infants (gestational age <28 weeks) who remain ventilator-dependent between 4-14 days of life will be randomized to receive either three weekly intravenous doses of UC-MSC (10x10^6 cells/kg/dose) or a sham procedure. The primary outcome is ventilation-free days (VFDs) at 120 days post-randomization, accounting for mortality. Secondary outcomes include cell administration safety, respiratory and neurodevelopmental outcomes, and complications of prematurity. A total of 168 participants will be enrolled to detect a clinically meaningful difference in VFDs. Ethics and DisseminationEthics approval has been obtained, and the trial is registered on ClinicalTrials.gov. Results will be disseminated via peer-reviewed publications, conferences, and public engagement platforms. Parent partners are actively involved in study design and dissemination to ensure relevance and transparency. Strengths and limitations of this studyO_LIVentilation-free day (VFD) is a clinically relevant primary outcome compared to BPD, as prolonged mechanical ventilation in preterm infants is directly associated with increased risks of mortality, neurodevelopmental impairment, and other complications, making VFDs a more sensitive and meaningful measure of both survival and recovery C_LIO_LIUse of a multiple-dose regimen and fresh cell product to optimize the cells therapeutic potential C_LIO_LICell product was tested in a large animal model of BPD C_LIO_LIParents involvement in the trial design and development to deliver meaningful research that benefits patients and increase study acceptance among parents. C_LIO_LIA sham procedure was chosen over a placebo based on parent feedback, which increased the risk of unblinding, but strategies to mitigate that risk were developed. C_LI