A stem cell therapy for hypoplastic left heart syndrome (HLHS), a serious congenital heart defect that affects blood flow through the heart, has entered a key clinical trial stage. The therapy aims to strengthen the heart and improve outcomes for children with the condition.[1]
What is HLHS?
In HLHS, the left side of the heart, which is responsible for pumping oxygenated blood through the body, does not develop properly in the womb. The left ventricle and related structures are small and underdeveloped.
Before birth, a baby’s circulatory system includes temporary connections between the two sides of the heart: a hole called the foramen ovale and a duct between the pulmonary artery and the aorta called the ductus arteriosus. Normally, these close shortly after birth as the baby begins breathing independently.
In babies with HLHS, these temporary connections are essential for oxygenated blood to circulate. Once they close, the underdeveloped left side cannot pump blood effectively, and the right side becomes overloaded. Symptoms appear within hours or days of birth and may include a bluish tint to the skin (cyanosis), cold extremities, lethargy, weak pulse, and difficulty breathing. Without intervention, HLHS is fatal.[2][3][4][5]
How is HLHS treated?
Babies with HLHS typically undergo a series of surgical procedures to reroute blood flow and support the single functioning ventricle. These surgeries are performed in three stages:[5][6]
- Norwood procedure – Rebuilds the aorta and connects it to the heart’s right ventricle, then links the pulmonary artery to enable the right ventricle to pump blood to the body. Usually performed within the first two weeks of life.[7]
- Bidirectional Glenn procedure – Connects the pulmonary artery directly to the superior vena cava, allowing oxygen-poor blood from the upper body to flow to the lungs, reducing strain on the heart. Typically done between 4–6 months of age.[8]
- Fontan procedure – Connects the inferior vena cava to the pulmonary artery, further improving oxygenated blood flow throughout the body. Generally performed at 3–4 years of age.[9]
These procedures allow many children with HLHS to survive into adolescence and adulthood.[4] However, the single ventricle remains under strain, eventually leading to heart failure and potential need for a transplant.[1][10] Transplants are limited by donor availability, and traditional heart failure treatments are more technically challenging in HLHS patients due to the unique single-ventricle physiology.[11]
How could stem cells help?
The stem cell therapy being trialled, laromestrocel, is administered in addition to standard surgery. It consists of mesenchymal stem cells (MSCs) derived from the bone marrow of healthy donors, injected into the heart muscle during the Glenn procedure.[10] Laromestrocel is an experimental therapy and is not yet approved as a standard treatment for HLHS.
MSCs have anti-inflammatory and regenerative properties. The therapy aims to strengthen the heart by stimulating new blood vessel growth and supporting the heart’s limited regenerative abilities. This could improve heart performance and may delay or reduce the risk of heart failure and the need for a transplant.[1]
In a previous Phase 1 clinical trial, the therapy was shown to be safe, with no major adverse cardiac events or treatment-related infections.[10][12] All patients remained alive and transplant-free five years after treatment, exceeding historical survival averages .[1][13]
The therapy has now advanced to Phase 2b, a randomised, double-blind, placebo-controlled trial. Forty infants with HLHS have been recruited across leading paediatric heart centres in the United States. Twenty will receive laromestrocel during the Glenn procedure, while the remaining 20 will receive standard surgery alone. Initial results are expected within a year, with follow-up planned for up to five years.[1][14]
Hope from stem cells
Regenerative medicine has drawn significant attention as a potential approach to strengthen the heart. Researchers are investigating stem cells from various sources, including bone marrow and umbilical cord tissue, to determine the optimal timing and method of administration in HLHS treatment.[15]
Laromestrocel is also being explored for other conditions where MSCs’ anti-inflammatory and regenerative properties may be beneficial, such as Alzheimer’s disease and age-related frailty.[12]
For children born today, storing stem cells may offer potential medical benefits in the future. Some stem cells, like those from bone marrow, are available throughout life. Others, such as cells from the umbilical cord or placenta, can only be collected at birth.
You can choose to preserve these cells for your child’s possible future use. Fill in the form below to receive our free guide and learn more.
References
[12] Longeveron (2022). Clinical Trials. https://longeveron.com/clinical-trials/
[13] Kaushal, S., Naioti, E., Ramdas, K. N., Mehranfard, D., McClain-Moss, L., Davis, M. E., Lambert, L. M., … Hare, J. M. (2023, November 6). Long-term transplant-free survival is improved in hypoplastic left heart syndrome with cell-based therapy. Circulation, 148(Suppl_1). https://doi.org/10.1161/circ.148.suppl_1.17067
[14] UTHealth Houston (2023). ELPIS II Study. https://sph.uth.edu/research/centers/ccct/elpis/
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Lesley-Ann Martin, PhD
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Dr. Martin holds a PhD in Molecular Biology from the University of Reading and has extensive research experience at the Institute of Cancer Research. She oversees all scientific and laboratory operations at Cells4Life.
