Three-dimensional cell models have evolved to bridge the gap between cell culture and animal models. Beyond traditional in vitro cell models, 3D cell models such as organoids more accurately recapitulate in vivo cell function. This enables researchers to create more precise model systems in the lab. Innovations in 3D cell modeling of lung, liver, brain, cancer, and other organs and disease tissues are now providing next-generation platforms for advancements in translational research and drug screening. These investigations will broaden our understanding of health and disease and potentially accelerate the pursuit toward personalized medicine.1
In vitro cell cultures have served as important research tools for modeling human development and diseases. Two-dimensional cell models were created to address limitations arising from cell monolayers, specifically the inability to model cell architecture and complexity. These 2D cultured cell models have limitations as well, falling short of accurately mimicking signaling, cell-cell communication, and structural networks crucial to native in vivo cell function.
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In response to these challenges, 3D cell model systems have more recently been engineered to accurately mirror biological attributes of in vivo cell networks.2 Three-dimensional cell clusters termed organoids or spheroids can be derived from embryonic stem cells, induced pluripotent stem cells, adult stem cells, and in certain cases, primary cells. Patient-derived sources of organoids can preserve the genetic lineage of the host and can be reflective of normal tissue or serve as disease-specific models. The scalability of patient-specific 3D cell models makes them ideal platforms for drug screening and precision medicine applications.
Organoids, spheroids, and organoids-on-a-chip
Three dimensional models vary according to complexity and application. Organoids are commonly defined as clonal derivatives grown from stem cells that self-organize and exhibit organ-specific architecture, cell-cell communication, and signaling.2 To generate organoids, progenitor cells (stem cells) are coaxed using growth factors, culture conditions, and other elements of the source microenvironment to differentiate into cells representative of the specific organ or tissue system.
At the hands of innovation, many of the methods used for organoid production have been optimized.
A similar type of 3D cell model to organoids, termed spheroids, are spherical cellular units that are cultured as free-floating aggregates of lower complexity compared to organoids. These spheroids can be used as suitable models of diseases such as certain types of cancers.3,4 Due to the ability to rapidly produce and expand spheroids, they are also useful in high-throughput screening for lead identification of therapeutic candidates.5,6
Organoids-on-a-chip systems include organoids that have been functionalized using microfabrication and microfluidic technologies. Applications of these systems include organ and tissue engineering using high-throughput and/or time-resolved analysis. Importantly, organoid-on-a-chip models can emulate the dynamic microenvironment of diseases such as cancer, providing unique insight into mechanisms of disease.7
The progression of 3D cell models into research and screening tools
The origin of 3D cell culture systems has a long history. It wasn’t until the advent of stem cell technologies, however, that it became apparent that 3D cell models and multiple organoid types could be generated from reprogramming and expanding native cells.8-11 The development of methods to create these various types of organoids from stem cells arose through multiple research pursuits.12-14
Method refinement coupled with technology innovation has propelled organoids from research tools to viable next-generation disease modeling and drug screening platforms.
As most researchers in the field can attest, however, there are challenges in cultivating organoids and bringing them into broader use. The first is precision. The delicate and fastidious nature of stem cells makes culturing and stable differentiation difficult. The second is scalability. Organoid development involves reprogramming small tissue samples, biopsies, or differentiated cells. Despite careful culturing and timing, expansion can lead to mixed populations of cells thereby affecting yields. Because of these and other factors, optimized methods are needed to move organoids from the research bench to large-scale applications such as multiplexed assays and screening campaigns.
The importance of organoid technology development
At the hands of innovation, many of the methods used for organoid production have been optimized. Standardized methods are now used to generate specific organoids and preparations can be automatically bio-printed into large-scale arrays.15 Functional assays and imaging analysis can be combined with other parameters to assess the effects of drug compounds on organoids over time. Machine learning tools can help resolve the temporal and spatial aspects of these effects and help guide further research and screening.
Defined media and reagents with strict quality control standards are available from commercial sources. Instruments and consumables are now designed to meet the standards of cell culturing and differentiation, resolving a large part of the variability in organoid production and yield. Technologies for liquid handling, imaging, and data analysis are now combined to offer complete organoid production and screening solutions. These include lab-based instruments for smaller-scale research applications, or complete work cells for high-throughput screening. Contract services are also becoming available for the generation of organoids outside of the lab in controlled production facilities.
Method refinement coupled with technology innovation has propelled organoids from research tools to viable next-generation disease modeling and drug screening platforms.
Outlook
Focus is shifting toward the clinical potential of organoids. Research groups are developing methods to tackle organoids from challenging tissues and difficult-to-study diseases. Instrument solutions providers are collaborating with scientists to bring these new methods to scale for multiplexed assays and screening pursuits. Recent announcements of collaborations between academic, clinical, and industry partners exemplify this vision.17
As the field evolves, future innovations will include multi-organoid systems. Body-on-a-chip or assembloid models, where multiple organoids derived with different tissues are brought together and integrated, will prove extremely valuable for complex disease research such as cancer where multiple organs become involved. Indeed, these next-level innovations are already underway in cardio-pulmonary (heart-lung), hepato-biliary (liver-kidney), blood-brain barrier, and other areas of assembloid modeling.12,18
References:
1. https://hsci.harvard.edu/organoids
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7. Wang H, Ning X, Zhao F, Zhao H, Li D. Human organoids-on-chips for biomedical research and applications. Theranostics. 2024; 14(2):788-818. doi: 10.7150/thno.90492
8. Junying Yu et al. Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells. Science. 2007; 318:1917-1920. DOI:10.1126/science.1151526
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10. Dolmetsch R, Geschwind DH. The human brain in a dish: the promise of iPSC-derived neurons. Cell. 2011; 145(6):831-4. doi: 10.1016/j.cell.2011.05.034
11. Corrò C, Novellasdemunt L, Li VSW. A brief history of organoids. Am J Physiol Cell Physiol. 2020; 319(1):C151-C165. doi: 10.1152/ajpcell.00120.2020
12. Yang S, Hu H, Kung H, Zou R, Dai Y, Hu Y, Wang T, Lv T, Yu J, Li F. Organoids: The current status and biomedical applications. MedComm (2020). 2023; 4(3):e274. doi: 10.1002/mco2.274
13. Adlakha, Y.K. Human 3D brain organoids: steering the demolecularization of brain and neurological diseases. Cell Death Discov. 2023; 9:221. https://doi.org/10.1038/s41420-023-01523-w
14. Choi SY, Kim TH, Kim MJ, Mun SJ, Kim TS, Jung KK, Oh IU, Oh JH, Son MJ, Lee JH. Validating Well-Functioning Hepatic Organoids for Toxicity Evaluation. Toxics. 2024; 12(5):371. https://doi.org/10.3390/toxics12050371
15. LeSavage, B.L., Suhar, R.A., Broguiere, N. et al. Next-generation cancer organoids. Nat. Mater. 2022; 21:143–159. https://doi.org/10.1038/s41563-021-01057-5
16. Cabral M, Cheng K, Zhu D. Three-Dimensional Bioprinting of Organoids: Past, Present, and Prospective. Tissue Eng Part A. 2024; 30(11-12):314-321. doi: 10.1089/ten.TEA.2023.0209.
18. Dao L, You Z, Lu L, Xu T, Sarkar AK, Zhu H, Liu M, Calandrelli R, Yoshida G, Lin P, Miao Y, Mierke S, Kalva S, Zhu H, Gu M, Vadivelu S, Zhong S, Huang LF, Guo Z. Modeling blood-brain barrier formation and cerebral cavernous malformations in human PSC-derived organoids. Cell Stem Cell. 2024; 31(6):818-833.e11. doi: 10.1016/j.stem.2024.04.019
