The development of organoids marks a turning point in biomedical research because organoids mimic human organs. They can be used to create realistic disease models and help reduce or even completely replace animal testing in accordance with the 3R principles.
The 3Rs – replace, reduce and refine – are ethical principles intended as guidance for the use of animals in biomedical and pharmaceutical research. In Switzerland, as in many other countries, the 3Rs are enshrined in law as protection for animals used for scientific purposes. For researchers, this means taking account of the 3Rs in all phases of animal testing, from planning to implementation. The aim is to conduct animal experiments only when there are no acceptable alternatives (Replace), to minimise the animals’ suffering during testing (Refine) and to keep the number of animals used as low as possible (Reduce). The three principles of minimising animal use in scientific experiments and maximising their wellbeing were formulated 65 years ago by British scientists William Russell and Rex Burch. A lot has happened since then. For example, the number of animals used in experiments in Switzerland has been reduced from two million to 600,000 in the last thirty years, with a corresponding fall in stress. The development and use of alternative methods to replace animal testing is central to successful implementation of the 3Rs. Organoids represent one highly promising alternative method.
The potential of organoids
Organoids are miniaturised three-dimensional tissue structures. They are cultured in laboratories and can mimic the basic properties of real organs, such as livers, intestines, kidneys, retinas and brains. Researchers use organoids to investigate organ development, disease mechanisms and the effects of medicines, and to better understand and model the complexity of human tissue and organs. Organoids also have the potential to accelerate and personalise the development process for new medicines and treatments.
Stem cells: the raw material for organoids
The fact that organoid production is possible at all is attributable to stem cell research and developmental biology. Stem cells are what are known as undifferentiated cells. They have an almost unlimited ability to divide and proliferate. Stem cells also have a high differentiation potential. This means they can form various specialised cell types. An embryonic stem cell, for example, is an undifferentiated cell because it is not yet clear which role of the 200 or so cell types in the body it will assume – in other words if it will become a liver, blood, muscle or nerve cell, for example. Embryonic stem cells have the capacity to form just about any cell type, which is why they are classified as pluripotent cells. The role of stem cells in adult organisms is to repair and maintain. Adult (somatic) stem cells make sure that organs and injured tissue regenerate.
Groundbreaking: induced pluripotent stem cells
One major breakthrough in stem cell research is the ability to transform a skin cell, for example, back into a human stem cell. Such engineered stem cells are known as induced pluripotent stem cells (iPSCs) and can be obtained by genetically reprogramming just about any normal cell that does not have stem cell properties. In simple terms, the cell is genetically reprogrammed and returned to its pluripotent, undetermined original state.
A potentially infinite resource
This form of stem cell engineering was made possible by progress in developmental and molecular biology and was first successfully performed by Japanese scientist Shinya Yamanaka in 2006. One groundbreaking advantage of iPSCs is that they free researchers from their reliance on embryonic stem cells. This is because induced pluripotent stem cells have regained their ability to develop into just about any type of cell in the body. For example, it is possible to generate patient-specific stem cells that can be used to model diseases or develop personalised treatments, for example. Induced pluripotent stem cells are a potentially infinite resource that can be used to drive medical and pharmaceutical progress, including work on organoids.
Three-dimensional cell structures that resemble organs
The word “organoid” comes from the Greek word “organon”, which means “tool”, “instrument” or “organ”. The “oid” ending denotes “similarity” to an organ. In other words, organoids are laboratory-cultivated cell groups that develop into a desired simulation of an organ under the best possible conditions. Each organoid is a bespoke three-dimensional tissue structure that is made from stem cells and possesses the ability to imitate the basic properties of a particular organ. The production process is complex. The stem cells – pluripotent or adult somatic stem cells – have to possess particular growth properties. Components such as specific nutrient supply have to be added to the three-dimensional cell group in a particular order or at certain times.
Stimulating organoid development
The challenge for the researchers working on and with organoids is to find the ideal conditions that stimulate and nurture the stem cells as they develop into organoids. This can take years. Once the formula has been found, however, the stem cells will proliferate and differentiate, creating cell-based structures and building three-dimensional organoids without external assistance. The challenge facing research and development scientists in the next few years will be to improve their knowledge by identifying the factors that stem cells and organoids need to increase their similarity to real organs, particularly as regards their surrounding environment, such as the immune system, blood vessels and nerves. In addition, the already broad spectrum of organs that can be investigated using organoids will continue to grow.
The current organoid spectrum
Miniature models of the brain are used to investigate neuronal development, conditions such as Alzheimer’s disease or autism, and the effects of medicines.
Models of the small and large intestine aid research into the intestinal barrier, microbiota and diseases such as Crohn’s disease and bowel cancer.
Models of the liver are used to investigate liver function, liver diseases (e.g. hepatitis) and to test medicine toxicity.
Reproductions of the airways are used in research into diseases such as COVID-19, asthma and other respiratory tract infections.
Miniature hearts that reproduce the contraction of heart tissue are used to research heart disease and to test medicines.
Kidney organoids are used to investigate and research kidney function and disease, including kidney failure and the effects of medicines.
Organoids are used to research diabetes, insulin production and pancreatic cancer.
Organoids model stomach structure and function for the purpose of researching ulcers, infections such as Helicobacter pylori and stomach disease.
Reproduction mammary gland tissue is used to investigate breast cancer.
Models of the retina and other parts of the eye for the purpose of investigating eye disease and impaired vision.
Organoids are versatile and potent
Organoids are playing an increasingly important role in the research and development of new medicines and treatments because they reproduce human organs and tissue more realistically than conventional cell cultures or animal models. As a kind of bridge between cell cultures and living organisms, they are frequently able to improve the accuracy and realism of research. Organoids have a huge range of applications.
Improving disease modelling
To give one example, organoids are used to investigate the development and course of diseases in detail. The pathologies and progression of conditions such as cancer and infectious diseases are modelled to gain an understanding of the biological mechanisms underlying disease progress or to identify potential molecular targets for new medicines.
Developing treatments for hereditary diseases
In the case of genetic diseases, organoids can help analyse the effects of specific genetic mutations on organ development by enabling researchers to create organoids using cells from patients with particular hereditary conditions. This provides a way of researching genetic disease as well as a platform for testing potential gene therapies or long-term treatments for hereditary conditions. Organoids are used in infectious diseases research to test the effects of pathogens such as viruses and bacteria on human tissue and to find potential treatments.
Enormous progress in personalised healthcare
Organoids play a particularly significant role in personalised healthcare, where organoids created from patients’ cells are used to build patient-specific disease models. As a result, various treatment options can be tested in vitro – in controlled laboratory conditions, in other words – to identify the most effective treatment. Tumour organoids are particularly important in cancer treatment as a way of finding the best treatment for individual patients. Furthermore, tumour organoids allow researchers to analyse tumour development and progression as well as metastases in detail and gain a better understanding of them. In addition, tumour organoids can be combined with cells from the immune system, for example, to simulate the immune system’s reaction (immune response) to cancer. This helps drive forwards immunotherapy, which aims to stimulate the body’s immune system to combat disease.
Improving the treatment of degenerative diseases
In regenerative medicine, organoids help researchers investigate the regenerative potential of stem cells and test ways of integrating them into damaged tissue. This opens the door for the development of potential approaches to the treatment of degenerative diseases such as diabetes and heart failure or new treatments for liver, kidney, lung or metabolic diseases.
Improving the specificity, efficiency and speed of medicines development
Finally, organoids offer major benefits in active substance screening and candidate selection, toxicity and safety assessments, and optimisation of the dosage and pharmaceutical form of new medicines. Organoids can be used in active substance screening to test large volumes of chemical compounds and identify potential medicines capable of influencing relevant disease-specific targets. They provide a more realistic environment in which to test human tissue’s response to the active substances. Since organoids replicate complex cell-to-cell interactions and tissue architectures, they provide more accurate predictions of the effects a medicine could have in the human body than simple cell cultures.
Pea-sized multi-talents revolutionising research and development
Although rarely bigger than a pea, organoids are nevertheless helping improve our understanding of how organs share tasks and the biochemical interactions that take place in our bodies. In the meantime, researchers are also able to link up various organoids on smartphone-sized plates. As a result, it is possible to replicate the interaction between processes in the body with ever greater accuracy, for example as a way of testing the metabolism of new medicines, in other words the chemical changes that the active substance undergoes in the body. This multiple-organ chip technology is likely to improve substantially over the next few years. The ultimate hope is to use organoid technology to create fully functional donor organs in the laboratory.
How organoids affect implementation of the 3Rs
Hopes are naturally high that organoids will one day completely supersede animal testing. While they are not yet able to do so, they can be used to reduce animal testing in many areas of research and medicines development, as well as to replace it in certain cases. At present, the scope for replacing animal testing with organoids is restricted primarily by the lack of system complexity. Complex interactions between different organ systems and the effects on the organism as a whole cannot yet be simulated sufficiently well using organoids and the systems that can currently be created. In many cases organoids still lack a real-world environment of blood vessels, nerves and an immune system. This limits their ability to fully reproduce certain processes, such as inflammation and immune responses. Moreover, since organoids still have difficulty completely simulating long-term processes such as ageing and chronic diseases, animal testing will remain necessary for the time being.
Progress will significantly reduce animal use
Nevertheless, organoids will increasingly be used to supplement animal testing, particularly in the early stages of research and active substance development. During this preclinical research phase, organoids can help improve the efficiency of potential active substance testing and make testing more human-specific before animal models are needed to investigate systemic effects. This will reduce the number of animal experiments required. With continuing progress, organoids will become increasingly capable of replacing animal testing, and the relevance of the results to humans will improve. However, it will still be some time before organoid technology can fully replace animal testing.
Sources:
- Federal Food Safety and Veterinary Office: The three Rs
- EuroStemCell
- Tierversuche verstehen: Alternativmethoden (in German)
- Tierversuche verstehen: Organoide (in German)
- Reatch (in German)
- Swiss Laboratory Animal Science Association (SGV) (in German)
- University of Bern (in German)
- Federal Food Safety and Veterinary Office: Animal testing statistics 2023 (in German)