# Adjunct cell therapy for hypoplastic left heart syndrome: therapeutic promise requires targeted design strategy

## TL;DR

This letter discusses the challenges of cell therapy for hypoplastic left heart syndrome and emphasizes the need for better study design.

## Contribution

The paper calls for improved consideration of cell delivery timing and myocardial development in future congenital heart disease studies.

## Key findings

- Unfavorable clinical findings were observed in a cell therapy trial for hypoplastic left heart syndrome.
- Study design challenges complicate the interpretation of cell treatment efficacy and safety.
- Future studies should align cell delivery with myocardial tissue remodeling and developmental growth.

## Abstract

Letter to the editor regarding: Gallego-Navarro C, Jaggers J, Burkhart HM, Carlo WF, Morales DL, Qureshi MY, Rossano JW, Hagen CE, Seisler DK, Peral SC, Nelson TJ. Autologous umbilical cord blood mononuclear cell therapy for hypoplastic left heart syndrome: a nonrandomized control trial of the efficacy and safety of intramyocardial injections. Stem Cell Res Ther. 2025 May 1;16(1):215. doi: 10.1186/s13287-025-04316-3. This phase IIb clinical cell therapy trial with autologous cord blood mononuclear cells is notable and highly commended as an important effort in very challenging clinical conditions in which new cell treatment advancements have been limited. In light of their findings of unfavourable clinical findings, our letter highlights that their study is intertwined with the complexity of the clinical pathology within immature pediatric hearts, cardiac surgical intervention strategy and other related study design hurdles. These difficulties contribute to confound the interpretation of cell treatment efficacy and clinical safety. Based on this study and our own recent clinical study, we make a call for future studies testing cell therapy in the congenital heart disease setting, to implement far greater consideration of the mode and timing of cell delivery and congruency with myocardial tissue remodelling and developmental growth processes in small hearts.