Human Brain Organoids Cultured for 5 Years in the Laboratory Replicated the In Vivo Epigenetic Timeline
Background
The maturation process of the human brain proceeds significantly more slowly than in other mammals. While mice complete brain development within weeks, humans undergo brain development over several years through infancy and adolescence. To study this complex maturation process in an ex vivo environment, human stem cell-derived three-dimensional brain organoid technology has gained attention.
However, existing organoid culture methods have been limited to cultivation periods of several months. These methods have only been able to recapitulate early fetal developmental stages, and long-term culture often leads to cell necrosis or genetic and epigenetic alterations, making it difficult to track normal developmental pathways. To comprehensively study the maturation and aging processes of the brain after birth, a culture system that can maintain long-term cell viability while accurately mimicking the natural developmental trajectory of the brain is essential.
Key Findings
A research team led by Professor Paola Arlotta from Harvard University and the Broad Institute successfully cultured organoids stably for more than 5 years. The key technology enabling this achievement is the Activity-Permissive Medium (APM), a culture medium that supports cellular activity. The research team modified the nutritional components of the commercial BrainPhys medium, reduced sugar concentration, and enhanced glutamine stability. This medium contributed to the survival and synaptic activity of neurons, preventing cell degeneration associated with long-term culture.
The research team conducted a comprehensive analysis of the DNA methylation patterns of organoids cultured for periods ranging from 3 months to 5 years. Applying epigenetic clocks such as Horvath's pan-tissue clock and a cortex-specific clock, the predicted epigenetic age of the organoids matched the actual culture duration precisely. The organoids preserved their overall methylation structure stably over the 5-year culture period.
Additionally, the study revealed the memory of time within the cells. The research team conducted an experiment in which neural progenitor cells (NPCs) isolated from aged organoids were transplanted into younger organoids. The transplanted NPCs did not revert to an early developmental stage but directly generated late-stage neurons according to their intrinsic developmental timeline. This indicates that the cells retain and execute their unique developmental trajectory over time, independent of external environmental signals.
Significance and Prospects
This study demonstrates that organoids cultured in the laboratory can serve as a powerful tool for accurately replicating the long-term development of the human brain. The human brain undergoes complex pruning and synaptic reorganization after birth to mature. Organoids cultured for 5 years offer an unprecedented opportunity to observe these postnatal changes at the molecular level. In particular, they are expected to be useful for elucidating the pathogenic mechanisms of complex neurodevelopmental disorders such as autism spectrum disorder (ASD) and schizophrenia, which begin in infancy or childhood.
Furthermore, the study opens new possibilities for modeling neurodegenerative diseases such as Alzheimer's and Parkinson's, which progress with aging. Due to the long time required to observe aging processes in human cells, it has been difficult to evaluate the long-term efficacy and toxicity of drug candidates. However, this organoid model, which remains healthy for 5 years, could serve as a solution.
Nevertheless, technical limitations remain before the technology can be widely adopted and commercialized. Cultivating organoids for more than 5 years requires significant costs and meticulous management. Additionally, the absence of blood vessels and immune cells such as microglia, which are present in the real brain, makes it difficult to fully replicate the brain's microenvironment. Vascular co-culture techniques and integrated immune system models are identified as key challenges to be addressed in future research.
Nature Medicine, Published online: 28 August 2026; doi:10.1038/d41591-026-00044-0Human brain organoids cultured for 5 years exhibit epigenetic aging dynamics that mirror those seen in vivo, which makes them a powerful tool for studying postnatal brain development.
A system capable of stably culturing organoids for several years has the potential to maximize the efficiency of drug development. Conventional drug screening methods have relied on short-term two-dimensional cell assays or mouse models, which differ from the human brain structure, making it difficult to detect long-term drug efficacy and chronic toxicity. The organoid technology that survives for 5 years can serve as a platform to observe the responses of various drug candidates, ranging from childhood developmental disorders to adult neurodegenerative diseases.
The most concrete scenario is the evaluation of Alzheimer's disease treatments. The chronic process of abnormal tau protein aggregation or amyloid-beta accumulation causing brain cell damage can be recapitulated within the organoids, and validation tests can be conducted by administering treatment candidates over several months or years, monitoring toxicity and neuroprotective effects over the long term. Additionally, by culturing organoids from patient-derived cells with specific genetic defects over the long term, it will become possible to predict disease onset and design patient-specific precision medicine solutions.