Leonard Zon, professor of stem cell and regenerative biology and Grousbeck Professor of Pediatrics at Harvard Medical School, has been awarded the 2026 March of Dimes Richard B. Johnston Jr., MD Prize.
A hematologist, stem cell scientist, and developmental biologist, Zon is an international leader in illuminating how blood develops in embryos. He pioneered the use of zebrafish as a model to study human disease, with a focus on blood diseases and cancers.
His work has deepened understanding of rare blood diseases, including in pregnancy, and led to new treatments for genetic blood disorders that affect infants and children.
The March of Dimes supports maternal and infant health research, education, and advocacy. The prize recognizes scientists whose work in developmental biology has transformed understanding of human health.
The organization noted that Zon’s research has direct applications for addressing pregnancy complications and childhood diseases.
“Dr. Zon’s groundbreaking work using the zebrafish to study human disease has resulted in truly amazing insights about the most devastating genetic disorders and cancers affecting the smallest patients,” said March of Dimes Chief Scientific Advisor Emre Seli.
“Incredibly, Dr. Zon has balanced seeing sick kids in the clinic with groundbreaking laboratory discoveries about pediatric disorders that have repeatedly stumped scientists,” he said. “His zebrafish work at the intersection of blood, cancer, genetics and induced pluripotent stem cells has transformed the way we understand and treat human disease.”
Demonstrating the value of zebrafish
In 1993, spurred by his desire to understand how blood develops and to mitigate rare yet devastating genetic blood diseases, Zon turned to the zebrafish, a 1.5-inch tropical fish with horizontal stripes, transparent embryos, and the ability to lay 300 embryos a week.
Zon was one of the first scientists to study zebrafish for the purposes of human disease. The unique sea creature has helped him make remarkable findings about human biology and disease treatment. Among them, he and his team:
- Illuminated the pathways of blood development in embryos, leading to a deeper understanding of rare blood diseases, including in pregnancy.
- Discovered ferroportin, the iron transporter gene that delivers the crucial micronutrient from mother to fetus.
- Identified a growth factor that exponentially increases stem cell populations for use in gene therapies for children with blood disorders, including sickle cell anemia.
With the help of the zebrafish, Zon led a team in the late 1990s that discovered five human genes never before implicated in blood diseases. The breakthrough electrified the field of hematology and crystallized zebrafish as not only a reliable but an outstanding model for human disease.
Of the five genes Zon’s team discovered, the most significant was the discovery of ferroportin in 2000. The gene ensures that iron, and thereby oxygen-carrying hemoglobin, is delivered from mother to fetus through the placenta.
This discovery transformed understanding of iron deficiency and anemia of pregnancy, a common condition worldwide that can lead to preterm birth and low birth weight. The finding opened new avenues for preventing and treating maternal anemia and its effects on fetal development.
Expanding stem cells to improve treatment
Zon, who founded the International Society for Stem Cell Research in 2002 and directs the stem cell research program at Boston Children’s Hospital, is also behind a transformative discovery around using stem cells to treat blood disorders affecting infants and children.
In 2007, his lab revealed that a hormone-like lipid compound called prostaglandin E2 could dramatically grow zebrafish stem cell populations. Human clinical trials in 2013 confirmed the lipid’s power: Adding it to donor umbilical cord blood increased the recipient’s stem cell populations by 400 percent, vastly improving transplant success for leukemia patients.
Today, the prostaglandin discovery is routinely used in stem cell gene therapy to treat genetic blood diseases in children — including sickle cell anemia, thalassemia, and primary immunodeficiencies — and has enabled advances in gene therapy techniques used by research teams worldwide.
Advancing the science and medicine of blood disorders
Zon’s discoveries continue to yield new treatments.
His zebrafish research has led to a novel therapeutic for Diamond-Blackfan anemia, which is now approaching human clinical trials. A treatment for the pediatric disease spinal muscular atrophy, developed by a company he founded, is currently under Food and Drug Administration review.
Other advances from his lab include:
- Spearheading the successful effort to sequence the zebrafish genome.
- Identifying a gene crucial for blood development (hematopoiesis).
- Discovering a genetic mutation involved in cell “trash removal” that contributes to many kinds of cancer.
- Developing a zebrafish-based screening platform to discover potential new drugs and regenerative medicine compounds, including for growing skeletal muscle cells and helping bone marrow transplants engraft, or “take.”
- Providing the first live imaging of how blood stem cells take root in the body.
- Capturing the first visuals of the origins of cancer from the first affected cell to its spread in a live animal.
- Creating a tool that color-codes living blood stem cells so scientists can track them over time.
- Demonstrating the first successful use of induced pluripotent stem (iPS) cells to make blood progenitor cells and identify potential drugs for Diamond-Blackfan anemia.
“Ever since my first experience working with leukemia patients early in my research career, I’ve been trying to uncover the mysteries of blood to help those affected by blood and other diseases,” said Zon, who is also a Howard Hughes Medical Institute investigator.
“So, to be instrumental in the discovery of new pathways that underscore blood development in embryos and to have a real impact on diseases affecting kids and babies, that’s priceless,” he said. “And to do it with the fascinating zebrafish and be honored for it is icing on the cake.”
Adapted from a March of Dimes news release.
