Harvard scientists have created human brain organoids that survived for up to seven years in lab conditions, setting a new longevity record and demonstrating the ability to record the passage of time
through biological processes like DNA methylation, according to a study published in Nature.
Researchers at Harvard University and the Broad Institute have achieved a milestone in stem cell research by cultivating human brain organoids that survived for up to seven years, far exceeding the previous record of 694 days. These lab-grown clusters of neurons, derived from human pluripotent stem cells, mimicked key developmental stages of the human brain, including the gradual maturation of neural networks and the activation of genetic programs tied to aging.
The Breakthrough Discovery
The study, led by Dr. Paola Arlotta, a professor at Harvard, revealed that organoids could replicate the molecular developmental sequence of human brains over extended periods. By optimizing culture conditions, the team sustained excitatory neurons for years, observing that the organoids’ biological age aligned with their time in vitro. The methylation clock told us that these organoids were basically doing things that the endogenous brain would do,
Arlotta said in a statement.
The breakthrough was detailed in a paper published in Nature, which included data from 110 organoids and nearly 425,000 individual cells. The researchers used single-cell RNA sequencing to track changes in gene expression over time, finding that early organoids matched first-trimester gene patterns, while those cultured for five years resembled aspects of a young child’s cortex.
How the Organoids Developed
Epigenetic analysis confirmed that the organoids’ DNA methylation patterns mirrored those of living human brains. The data indicate that human brain organoids record the passage of time following endogenous milestones and using similar epigenetic mechanisms,
the study stated. This capability allows researchers to study late-stage brain development, which is critical for understanding disorders like schizophrenia and autism.
The organoids were created using cells from the Coriell Institute for Medical Research and the California Institute for Regenerative Medicine. Researchers reprogrammed blood or skin cells into pluripotent stem cells, then guided their differentiation into neural progenitors. The team also collaborated with the Harvard Stem Cell Institute to ensure ethical compliance, with all experiments approved by the Harvard University IRB and ESCRO committees.
Implications for Research
The extended lifespan of these organoids opens new avenues for studying human-specific brain development, which traditionally spans nearly two decades. Animal models cannot fully capture this complexity, but the organoids now allow scientists to observe postnatal-like maturation in a dish. The brain can continue to develop outside the context of a person for this unprecedented amount of time,
Arlotta noted.
The research also has potential applications in drug testing and disease modeling. For instance, organoids could be used to study how Alzheimer’s disease progresses or to test therapies for neurodegenerative conditions. We can unlock a whole spectrum of human brain biology that we didn't see before,
Arlotta said.
However, ethical questions remain. Organoids currently occupy a regulatory gray area, neither classified as persons nor animals. Philosophers debate whether advanced organoids could achieve sentience, though no framework exists to determine this. The practical limit on size—currently around five millimeters due to oxygen deprivation—also restricts their complexity. Researchers at Johns Hopkins are now exploring artificial blood vessels to overcome this hurdle.
Future Directions
While the team has not sought to break their own record, they plan to refine the technology to study later stages of brain development more efficiently. We have shown it’s possible—a proof of principle—but clearly we need to figure out how to use the newly gained knowledge to enable understanding of later stages of development without having to wait years for organoids to grow,
Arlotta said.
The study’s findings could also influence broader biomedical research. In 2025, the U.S. National Institutes of Health redirected funding away from animal-only studies, investing $87 million in standardized organoid modeling. This shift underscores the growing importance of lab-grown tissues in replacing traditional research methods.
As the field advances, the Harvard team’s work represents a significant leap in understanding human brain development. By replicating the passage of time
in a controlled environment, these organoids offer a powerful tool for studying both normal maturation and the origins of neurological disorders.