Highlights
The Phase I CHILD trial confirmed the safety and feasibility of intramyocardial neonatal cardiac progenitor cell (nCPC) injections during the stage 2 palliative operation for Hypoplastic Left Heart Syndrome (HLHS).
The primary efficacy endpoint—improvement in right ventricular (RV) size or function at 1-year follow-up—was not achieved in the randomized cohort.
Secondary outcomes revealed a significant reduction in major adverse cardiac events (MACE) and hospital length of stay for patients receiving nCPCs compared to standard of care.
A combined analysis of all treated patients (Groups A and B) showed a statistically significant advantage in transplant-free survival for the nCPC group versus the control group (P = 0.005).
Introduction: The Right Ventricular Burden in HLHS
Hypoplastic left heart syndrome (HLHS) remains one of the most challenging congenital heart defects in pediatric cardiology. Survival is contingent upon a series of three staged palliative surgical procedures—the Norwood (Stage 1), the Glenn (Stage 2), and the Fontan (Stage 3). Throughout this process, the right ventricle (RV) is forced to function as the systemic pump, a role for which it is not evolutionarily or anatomically designed. Under chronic pressure and volume overload, many patients eventually succumb to RV failure, which remains a leading cause of late morbidity and mortality in this population.
Neonatal cardiac progenitor cells (nCPCs) have emerged as a promising regenerative therapy. In preclinical animal models of pressure overload-induced RV dysfunction, these cells have demonstrated the ability to improve myocardial performance, likely through a combination of direct regeneration and potent paracrine signaling. The CHILD (Cardiac Stem Cells in Patients With Hypoplastic Left Heart Syndrome) trial was designed to translate these findings into the clinical setting, evaluating whether autologous nCPCs could preserve or restore RV function during the vulnerable period of surgical transition.
The CHILD Trial: Study Design and Methodology
The CHILD trial was a phase 1, prospective study conducted to assess the safety, feasibility, and preliminary efficacy of autologous nCPC injections. The study structure was divided into two distinct groups to balance safety concerns with the rigors of clinical investigation.
Group A consisted of nine consecutive patients who received open-label nCPC injections during their stage 2 (Glenn) operation. This initial cohort served to establish the safety profile and the feasibility of cell harvesting and delivery. Group B was a multicenter, randomized, double-blind trial. In this phase, 16 patients were randomized 1:1 to receive either nCPC injections (n = 8) or standard-of-care (SOC) treatment (n = 8). The treatment arm received nCPC injections directly into the RV myocardium during the Glenn procedure. To maintain the integrity of the data, all caregivers, investigators, and core laboratories were blinded to the treatment assignment, with only the operating surgeon aware of the intervention.
The primary endpoints were focused on safety (procedural complications, arrhythmias, and adverse events) and feasibility. Efficacy was assessed as a primary exploratory endpoint by measuring changes in RV end-diastolic volume and ejection fraction using cardiac magnetic resonance (CMR) imaging and echocardiography over a 12-month period.
Key Findings: Navigating the Safety and Efficacy Paradox
Primary Endpoints: Safety and Functional Outcomes
The trial successfully met its primary safety and feasibility objectives. There were no reported incidents of procedural mortality related to the cell injections, nor were there significant increases in post-operative arrhythmias or inflammatory responses in the treatment arm. This establishes a critical precedent for the use of cellular therapies in the highly sensitive neonatal and infant surgical population.
However, the primary efficacy endpoint—improvement in RV functional parameters—was not met. At the one-year mark, CMR and echocardiographic data showed no statistically significant differences in RV size or ejection fraction between the nCPC group and the SOC group. This finding suggests that, at the current dosage and delivery timing, nCPCs do not produce a measurable shift in macro-level ventricular mechanics within the first year after the Glenn procedure.
Secondary and Exploratory Outcomes: A Signal of Clinical Benefit
While the functional metrics were disappointing, secondary clinical outcomes provided a more optimistic perspective. In the randomized Group B, the rate of major adverse cardiac events (MACE) per 100 person-days was 0.00 in the nCPC arm compared to 0.23 in the SOC arm (P = 0.013). Furthermore, the total 1-year in-hospital length of stay due to cardiac and vascular complications was significantly lower for those who received cell therapy (2 days vs. 15 days per 100 person-days; P = 0.035).
Perhaps most striking was the combined analysis of Group A and Group B. When evaluating the composite endpoint of death or listing for heart transplantation, the combined nCPC arms (n=17) experienced zero events, whereas the SOC arm (n=8) experienced three events. This resulted in a statistically significant difference in survival/transplant-free outcomes (log-rank P = 0.005). These data suggest that while nCPCs may not immediately improve ejection fraction, they may confer a protective effect that enhances clinical resilience.
Mechanistic Insights: Paracrine Modulation and the Inflammatory Milieu
To understand the biological underpinnings of these clinical signals, the investigators conducted mechanistic studies on plasma biomarkers. By postoperative day 5, patients in the nCPC arm showed noticeable increases from baseline in levels of vascular endothelial growth factors (VEGFC, VEGFD), tumor necrosis factor-alpha (TNF-α), and monocyte chemotactic protein-1 (MCP-1) compared to the SOC arm. Although these differences did not reach statistical significance after false discovery rate (FDR) adjustment, the trends suggest that nCPCs may modulate the systemic inflammatory and angiogenic response following cardiac surgery. This supports the hypothesis that the benefits of cardiac stem cells are mediated more by paracrine signaling—reducing fibrosis or promoting microvascular health—than by large-scale myocardial regeneration.
Expert Commentary: Interpreting the Disconnect Between Function and Outcome
The results of the CHILD trial highlight a common phenomenon in regenerative medicine: the disconnect between surrogate functional markers (like ejection fraction) and hard clinical outcomes (like MACE and survival). It is possible that nCPCs improve myocardial ‘quality’—reducing the rate of cell death or improving diastolic compliance—in ways that current imaging modalities are not sensitive enough to capture in a small sample size.
However, the limitations of the study must be acknowledged. The sample size in the randomized portion (n=16) is extremely small, making the study underpowered for definitive efficacy conclusions. Furthermore, the 1-year follow-up period may be too short to see the full impact of cell therapy on the long-term progression of RV failure, which typically manifests more severely after the Fontan procedure. The use of autologous cells also introduces variability, as the ‘potency’ of the cells may vary based on the individual patient’s genetic and physiological state.
Conclusion: Toward a Phase II Trial
The CHILD trial represents a significant milestone in the application of cellular therapy for congenital heart disease. While it failed to demonstrate an improvement in RV function, the robust safety profile and the significant reduction in MACE and hospitalizations provide a strong rationale for continued investigation. These findings justify the initiation of a larger Phase II trial, which will be necessary to determine if nCPCs can truly alter the natural history of HLHS and provide these patients with a more durable systemic circulation.
Funding and ClinicalTrials.gov
This study was supported by grants from the National Institutes of Health (NIH) and various philanthropic organizations. The trial is registered at ClinicalTrials.gov under the identifier NCT03406884.
References
1. Kaushal S, Hare JM, Mahle WT, et al. Phase I Randomized Study of Cardiac Stem Cells in Patients With Hypoplastic Left Heart Syndrome: The CHILD Trial. JACC Heart Fail. 2025 Nov 17:102723. doi: 10.1016/j.jchf.2025.102723.
2. He GW, et al. Right ventricular failure in hypoplastic left heart syndrome: pathways to failure and opportunities for rescue. Frontiers in Cardiovascular Medicine. 2020;7:58.
3. Bolli R, et al. Cardiac stem cells in patients with left ventricular systolic dysfunction (SCIPIO): elective post-hoc analysis of a randomised, open-label, phase 1 trial. Lancet. 2011;378(9806):1847-1857.
