Researchers speak out

Using genetically modified mice, we discovered how miniature organs of animals and humans can be grown in the laboratory. Organoid technology is now one of the New Approach Methodologies (NAMs). The strength of organoids lies in their simplicity, but that is also their weakness: organoids reveal fundamental principles at the organ level, but not at the level of the whole organism. The whole is always greater than the sum of its parts. Animal studies and clinical trials will remain essential for a long time to come.

I am not personally involved in animal experimentation. Nevertheless, I am of the opinion that, when conducted under strict conditions, animal studies remain indispensable for unraveling the fundamental principles of the brain. This is a crucial prerequisite for the diagnosis and treatment of the many brain disorders that, with the ageing population, are expected to increase in prevalence.

We want people to live longer, healthier lives. That is why we conduct research that generates the maximum amount of knowledge while using as few animals as possible. We combine excellent animal care, biobanks, advanced data analysis, and innovative animal-free methods (NAMs). Together with research in non-human primates, which share important biological similarities with humans, these approaches contribute to the development of new treatments for infectious diseases, Parkinson’s disease, aging-related conditions, and Long COVID, among others. At the same time, we are committed to reducing animal use wherever possible.

I am certain that contemporary immunotherapies for various forms of metastatic cancer and autoimmune diseases would simply not exist without animal experimentation.

Animal models are essential for understanding complex brain disorders. They provide the only means of studying the interactions between brain cells, blood vessels, and the rest of the body. Complex endpoints that are highly relevant to patients—such as motor function and behavior—can only be investigated in a complete living organism. At the same time, we actively employ alternative approaches, including cultured (stem) cells and AI. Scientific progress requires not an either-or approach, but a careful integration of complementary models.

Neurological and psychiatric disorders represent the greatest disease burden in the Netherlands. Addressing this challenge requires a deeper understanding of how the brain functions. Existing animal-free research methods and studies in humans are not yet able to answer many fundamental questions. Animal research therefore remains necessary to generate the knowledge and develop the models needed to better understand the brain and to create new treatments for neurological and psychiatric disorders.

I am trying to understand how we turn our experiences into knowledge about the world, and how sleep supports this process. To do this, I combine research in mice, rats, humans, and computational models. Each of these enables me to use different methods to study specific aspects. Together, these approaches complement each other and allow me to build a more complete understanding of how memory works.

At the Hubrecht Institute, we actively invest in animal-free research models, including organoids and embryo-like structures. These innovative technologies are transforming biomedical research, but they cannot yet capture the full complexity of embryonic development, organ function, or diseases such as cancer, diabetes, heart failure, and developmental disorders. For now, animal research remains indispensable for advancing fundamental knowledge and enabling the biomedical breakthroughs that improve human health.

I believe it is important that effective treatments are available to prevent, treat, and cure severe diseases. Animal research plays an essential role in achieving this. It helps us to better understand the complex biological processes underlying diseases and it supports the development of new therapies. In some cases, non-human primates are indispensable because their immune systems and brains closely resemble those of humans. We use non-human primates only when no suitable alternative exists and always under strict ethical and legal conditions.

The NVvI is committed to excellent immunological research that contributes to better health, disease prevention, and improved therapies. We emphasize the importance of selecting the most scientifically appropriate research models, ensuring that researchers use the best available approaches and technologies. Both innovative human-based models and carefully conducted animal research contribute to answering complex immunological questions.

Our researchers use both animal and non-animal methods to study diseases and develop new treatments. Cell cultures, organoids, human brain tissue and computer models provide valuable insights and reduce the need for animal use, but they cannot fully replicate the complexity of a living organism. Animal studies are important to help us understand how treatments affect the whole body. Molecules, cells and tissues can behave very differently inside a complex and intact body compared to in isolation in a petridish. By combining both approaches, we use the strengths of each to advance medical research as responsibly and effectively as possible.

Much of our understanding of the relationship between the brain, cognition, and behavior has been built through research involving animal models. Many of the discoveries that have transformed our knowledge of learning, memory, and addiction would not have been possible without it. Animal research has played a crucial role in advancing neuroscience and medicine, and it will continue to be an important part of future scientific progress.

We use animal experimentation in order to understand brain dynamics related to complex behavior at a level of detail that is impossible to obtain from human subjects. Many of those results become then the basis for our understanding of human brain and are, for what is technically possible, confirmed by results in humans. We also use animal experimentation for the development of brain interface technology meant to help paralyzed and sensory impaired human patients.

We study how disrupted protein balance and cellular communication contribute to neurodegenerative diseases such as Parkinson’s disease. Using human cellular models and animal studies, we aim to understand disease mechanisms and identify new therapeutic strategies.

As a brain researcher, I work on developing new treatments for serious neurological disorders, including blindness. NAMs help us make research more effective and targeted. However, to understand how treatments work and how safe they are in living brain networks, animal research is sometimes still necessary. Both approaches complement and strengthen each other.

In my research group, we work with a combination of behavioral experiments and neuroimaging techniques in humans, artificial intelligence, and advanced imaging techniques in rhesus macaques. Major advances in our field can only be achieved by integrating different methods and approaches. I see animal research as a tremendous responsibility: to care for the animals in my laboratory as well as possible, to conduct animal experiments in the most rigorous and controlled manner, and to use animals only when there is truly no alternative.

Together with my team, I study the importance of play for the development of the brain and behavior. Animal research on the effects of limited play opportunities early in life is particularly relevant and timely, as play is increasingly under pressure while mental health problems among young people are on the rise. Research on play and brain development in children is very limited for ethical reasons, whereas studies in animals provide compelling and in-depth insights into the importance of play.

Our group studies the biology of neurodevelopmental disorders with the goal of translating findings from the laboratory into better care for patients. Because disease mechanisms are not always the same across species, we use different research methods alongside each other, including mice and stem cell-derived systems. Model choice is guided by the clinical question. NAMs and animal models are not opponents, but tools for different levels of biological complexity. We match each tool to the question being asked.

Using advanced preclinical imaging techniques, such as MRI, I contribute to responsible animal research by obtaining more information from the same animals, following the same animals over time, and reducing experimental variation. In this way, we improve the quality, reproducibility, and translational value of preclinical research.

Animal research is essential for advancing healthcare. Through this type of research, we significantly reduce the risks associated with treatments and medical care for patients.

The use of laboratory animals is essential in research on metastatic cancer. In particular, the study of dormancy (viable tumor cells that are not actively dividing) and tumor recurrence requires in vivo models such as mice and rats.

I study how the brain transforms visual and other information into behavior. To do this, we use a range of different techniques. Some research questions can only be answered with the help of studies in mice.

Animal research is essential for unraveling the molecular mechanisms underlying neurodegenerative diseases and for developing effective treatments for these conditions.

My research focuses on chronic inflammatory diseases and metabolism. Both subjects affect multiple organs and tissues in an organism. In vitro we study metabolism and inflammation in cultured cells. To gain a deeper understanding on the interplay between distinct cell types and organs, studies in mice are essential.

In my experience, medical progress is only possible through a combination of research methods. Ideas are first tested using existing scientific literature and animal-free models, but when complex biological interactions are involved, animal research is sometimes still necessary. This is never done automatically. In my work with Animal Ethics Committees (DECs) and as chair of the Animal Welfare Body (IvD), I see every day how critically the necessity, ethics, and available alternatives are assessed, with great attention to animal welfare.

Understanding complex biological systems requires complementary models with different levels of complexity. In vascular dementia, animal research remains essential because the disease develops over time and involves ageing, long-term risk factors, blood pressure and blood-flow changes, mechanobiology, interactions between multiple brain cell types, and cognitive outcomes. In vitro models and NAMs are therefore valuable, but animal models remain part of this necessary toolbox.

Research using laboratory animals has enabled me to conduct clinical studies on new diagnostic methods and treatments for heart diseases such as heart failure, atrial fibrillation, and angina, and to pass this knowledge on to cardiologists in training. Without animal research, these advances in the care of patients with heart disease and the training of cardiologists would not have been possible. Models that contain only one or two cell types cannot adequately represent heart diseases, which often involve complex interactions between multiple organs and body systems.

We study the mechanisms underlying neurodevelopmental disorders, such as intellectual disability, autism, and epilepsy, as well as potential treatments for these conditions. We make extensive use of human (patient) stem cells derived to investigate changes at the molecular and cellular level. However, to truly understand how these processes disrupt brain development, and to test whether medicines can improve brain function, animal research remains indispensable.

We are making progress in developing animal-free models of the heart, but we still cannot reproduce all the relevant properties of the human heart in the laboratory. Therefore, studies in animal-free models are combined with carefully considered studies in animal models to test the effectiveness and potential side effects of new therapies for heart disease. This combined approach has recently led to a new treatment for inherited heart diseases.

Unfortunately, we are still dependent on animal research for the development of new gene therapies for heart disease. Despite the many promising alternatives being developed, such as stem cell models, animal research remains truly essential.

Thanks to our research using genetically modified mice with defects in DNA repair, children with similar conditions are now living much longer and with a greatly improved quality of life. This research has helped us identify an important cause of ageing, better understand and potentially slow age-related diseases, improve chemotherapy and surgery, and offers real hope for preventing neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. Without this animal research, these advances would not have been possible.

Animal experimentation is outmost necessary for the fundamental understanding of molecular sciences. Cell and tissue models cannot reproduce the complexity of the living organism. However, more funding should be available for finding and perfectioning such models. Until then, animal experimentation will remain necessary.

Improving our understanding of disease and developing new treatments still requires the use of laboratory animals, as alternative methods are not yet sufficiently reliable. My research focuses on drug distribution in the brain, with a strong emphasis on the refinement, reduction, and replacement of animal experiments. Using carefully designed animal studies, we were able to develop the LeiCNSPK3.0 computermodel, which allows us to accurately predict drug distribution in the human brain. This is a much more efficient way of working towards the replacement of animal experiments.

We study the health effects of specific nutrients in early-life, representing ages from babies into toddlers. Isolation of tissues to investigate molecular changes cannot be done in humans, so we use preclinical models (fruitflies and mice) for our fundamental physiological research. Identified pathways underlying the beneficial health effects in early-life, effects that last into adulthood, opens up avenues to improve e.g. infant formula. This is impossible without animal studies.

I investigate how viral infections such as SARS-CoV-2 can cause lasting changes in the brain that may contribute to neurodegenerative diseases such as Alzheimer's and Parkinson's disease. To address this, we combine research using macaques, samples from patients with long COVID, and stem cell-derived brain models. Because no single model can fully replicate these complex diseases, progress depends on a responsible combination of research methods as well as the continued development of more human-relevant alternatives.

Just as television did not replace radio, and computers did not make television obsolete, animal experiments are likely to remain necessary for the foreseeable future. However, by developing increasingly sophisticated models, such as organoids, that bridge the gap between cell cultures and living organisms, we can substantially reduce the number of animal experiments needed. Ultimately, we hope that animal experiments will only be required in exceptional circumstances—or perhaps become unnecessary altogether.

Animal-free research is a worthwhile goal, and I am actively involved in developing alternatives to animal testing because not everything needs to be tested in animals. However, I am not yet convinced that all research can be conducted entirely without animal models. For these specific experiments, animal studies must remain available to enable the successful clinical translation of our innovations. Only by combining advanced human-relevant models with carefully justified animal research can we ensure that new therapies are both safe and effective before they reach patients.

As a pathologist and coordinator of the BPRC tissue bank, I see how valuable biological material from non-human primates is for researchers worldwide. At the same time, through my involvement in research on infectious diseases, neurodegenerative disorders, and immune diseases, I recognize that animal research remains necessary in certain research areas. Together, these research approaches help us to better understand diseases and develop new treatments.

I conduct research using animal models to develop new preventive and therapeutic treatments for life-threatening diseases in humans.

To develop new therapies against malaria, a thorough understanding of both the parasite and the host is essential. Currently, there is no perfect model for malaria; different models complement one another. In our research, we combine NAMs (New Approach Methodologies) with non-human primate models to help bring us closer to the eradication of this disease.

Responsible research involving non-human primates, in which animal welfare and scientific quality go hand in hand, is essential for the European scientific ecosystem—from pandemic preparedness to strategic autonomy, and from One Health to research and innovation.

Brain aging is one of the most complex challenges in biomedical science. To understand how the brain remains healthy—or conversely, how it becomes diseased—we need models that closely resemble the human brain. Research involving non-human primates provides unique insights that cannot yet be obtained through other methods alone.

In my work at the UMC Utrecht, I use advanced human in vitro and ex vivo models to better understand cardiovascular diseases. My goal is to contribute to the development of better therapies for patients. Yet, despite recent advances, these models do not fully capture all the interactions that occur within the body. Hence, combining advanced human pre-clinical models with animal testing is essential to fully assess the safety and efficacy of new therapies.

For the development of new treatments for brain and neurological disorders, alternatives to animal research are not yet sufficient. The necessary animal studies will therefore continue to be conducted, whether in the Netherlands or elsewhere in the world. Responsible animal research therefore remains essential for advancing medical science and developing new therapies.

To me, research with and without animal models are not opposites; they actually complement each other. As a PhD candidate working with PET-CT, I see every day how different research methods provide essential pieces of the puzzle needed to unravel complex disease processes. It is precisely the combination of advanced imaging techniques and various research models that enables us to better understand processes within the body, and that is what makes this field so fascinating to me.

As an imaging specialist, I directly observe processes in the human body. Using PET-CT, we study, among other things, the effects of Long COVID and monitor disease-related changes over time. No single model can fully capture biological reality, so the integration of multiple complementary models provides the best approximation. That is why both innovative animal-free methodologies and non-human primate research remain important. Together, they contribute to a deeper understanding of complex diseases and the development of future therapies.

Without rigorous animal research, it will not be possible to sustain the significant progress made in the treatment of cardiovascular diseases, particularly at a time when the development of targeted therapies is accelerating.

For me, responsible biomedical research begins with respect for laboratory animals. That is why, for more than 25 years, I have been committed to the welfare of non-human primates that make an indispensable contribution to scientific research. In our breeding colony, the animals are raised in stable social groups, with considerable attention given to environmental enrichment and targeted animal training. In this way, we create the best possible conditions and ensure that the primates experience as little stress as possible during research procedures.

I conduct animal research to investigate the mechanisms and functions of sleep. Sleep is such a fundamental biological process that its importance often only becomes apparent when the ability to fall or stay asleep is disrupted.

In my research on heart failure and heart transplantation, we increasingly apply innovative non-animal models. Nevertheless, animal models remain necessary in specific contexts, for instance to evaluate the safety and efficacy of novel therapeutic approaches and transplantation strategies. Scientific progress therefore depends on a carefully considered integration of non-animal methods and animal research, with the most appropriate model selected on a case-by-case basis.

It is of uttermost importance that research into serious and life-threatening diseases is conducted in a rigorous and responsible manner. In cases where no suitable alternatives are available, animal experiments remain indispensable. This is particularly true for research on the immune system during the development of new vaccines, as well as for research on infectious diseases such as malaria, and brain disorders.

We all bear the responsibility to identify, develop, and implement alternatives to animal experimentation. At the same time, the responsible use of laboratory animals in the service of medical science remains indispensable at present. Governments should provide additional funding to support the development of such alternatives.

My team conducts research to understand how memories are stored and how these processes become disrupted in conditions such as dementia and post-traumatic stress disorder (PTSD). Animal-free alternatives are valuable for developing new interventions, but animal studies remain essential for elucidating the relationship between behavior, memory, and brain function. This complexity cannot currently be replicated in cell cultures or computer simulations.

I am a neuroscientist with extensive experience in preclinical research, animal behavior, neuroimaging, and data analysis. My work focuses on understanding brain function and developing innovative approaches for neurological disorders. Combining expertise in experimental design, behavioral testing, MRI, and computational analysis, I am passionate about translating scientific discoveries into meaningful advances for brain health and biomedical research.

As a drug discovery researcher in neuroscience, I use animal models to test candidates in vivo and as a source of primary cells and tissue. Animal research remains essential: candidates must be tested in complex biological systems where multiple cell types interact — something animal-free models cannot yet replicate. I prioritize alternatives and welfare, but restricting animal research in the Netherlands displaces it to countries with weaker regulation — worse for animals and patients.

As a cardiovascular researcher, I develop human-relevant models such as living myocardial slices, hiPSC-derived cardiac tissues, and bioengineered heart constructs to improve translation and reduce animal use. However, animal studies remain necessary for assessing the safety, biodistribution, and long-term effects of regenerative and gene therapies. Medical progress requires both innovation in New Approach Methodologies (NAMs) and responsible animal research.

Animal research proved indispensable in closing an important knowledge gap in tubulin research. Earlier cell culture studies suggested that a specific chemical modification of tubulin, a key component of the cytoskeleton, was essential for cell division and therefore highly relevant to cancer research. Follow-up studies in animal models demonstrated that the protein complex responsible for this modification is not required for cell division, but instead plays a crucial role in brain development. Without animal research, the scientific community would have remained on the wrong track.

My research group studies glioblastoma, a highly aggressive form of brain cancer. Because these tumors are extremely complex, the effectiveness of potential treatments cannot be adequately assessed using laboratory dish experiments alone. We therefore follow-up by evaluating promising therapies in mouse models of brain tumors. Without such testing, many patients—who are already suffering greatly from this devastating disease—could be unnecessarily exposed to treatments that ultimately prove ineffective.

In our research on ischemic heart disease (insufficient oxygen supply to the heart muscle), animal studies have generated a wealth of scientific knowledge over the past decades and have revolutionized the treatment of these conditions. New animal-free research methods, including so-called organ-on-a-chip models, are powerful tools that complement animal research to a high degree. However, they are unlikely to ever fully replace research in animal models.

I do not conduct animal research myself. However, as a physician, I treat people with various forms of rheumatic disease, often with good results. Without conducted animal research, I would have far less to offer these patients. I also conduct clinical research to improve the treatment of these diseases in the future, and that research, too, would be impossible without the groundbreaking animal research that precedes it.

I work as an education and research staff member within the Department of Nuclear Medicine and Molecular Imaging. My activities focus on conducting, facilitating, and coordinating animal research. This research supports the development and validation of innovative imaging techniques, PET tracer development, and Targeted Radionuclide Therapy (TRT), and forms an essential link in the translation of fundamental knowledge into clinical applications.

Research involving animals forms the foundation of much of our current understanding of the causes of brain disorders. It provides the basis for the development of new therapies and medicines. It is encouraging that new technologies can reduce or even eliminate the need for some animal experiments, but many important scientific questions still cannot be answered using these approaches alone.

We perform research on the mechanisms of new drugs for the treatment of lung and brain diseases, next to state-of-the-art innovative models, we need to perform in animal models such as mice, guinea pigs and due to their translational value (in the future) pigs.

My research studies metabolic disease progression and treatment. These diseases involve whole-body multi-organ interactions (liver, pancreas, muscle, adipose) affecting glucose, lipids and inflammation. Cell culture and computational models show limits but lack organ crosstalk and systemic homeostasis. Therefore, animal models are needed for physiologically relevant translational results.

Unfortunately, animal testing remains necessary for the development of treatments for diseases. It is increasingly possible to replace many animal experiments with disease models in the laboratory. However, the human body is so complex that we cannot yet rely solely on laboratory models. Therefore, animal testing remains necessary.

The interaction between a tumor and its host is highly complex. Many of the recent advances in cancer treatment are aimed at targeting this interaction. Animal research remains crucial for deepening our understanding of cancer biology and for developing therapies that can transform cancer into a manageable chronic disease.

Innovations in cardiology have greatly improved the quality of life of patients with heart disease and significantly extended their life expectancy. Thorough, high-quality animal research has been a crucial link in making these advances possible.

Both laboratory-based studies and animal experiments are essential for the advancement of scientific knowledge and the development of new medicines. Although alternative research methods are becoming increasingly important, they are currently unable to fully replace animal studies. Therefore, maintaining carefully regulated animal research in the Netherlands remains crucial for the continued progress of medical and biological science.

My research focuses on improving the diagnosis and treatment of stroke. To achieve this, I use animal models to unravel underlying biological mechanisms and to develop novel therapeutic interventions. I translate these findings into clinical studies involving patients. Animal research, in combination with other research approaches, including non-animal methods, remains indispensable for generating the scientific insights required to drive breakthroughs in clinical practice.

As we live longer, brain diseases are affecting more and more people. Cell cultures help us learn a great deal about healthy and diseased brain cells, but cells in a dish do not always behave the same way as they do in the living brain or respond to medicines in the same way. To better understand brain diseases and develop effective treatments, animal research remains necessary.

I build models of the brain to help us understand how it works, what we can measure, and how to test competing ideas. But models cannot replace experiments. We still know too little about the brain to create meaningful models without experimental data. Models help us design better experiments, and experiments help us build better models. This partnership between theory and experiment is at the heart of progress in neuroscience—just as it is in physics.

Our goal is not just to help people live longer, but to help them stay healthy for longer. We study ageing using human cells, organoids, artificial intelligence, and animal models. While alternative methods are becoming increasingly important, animal research is still needed to understand the complex interactions between organs, the immune system, and metabolism, and to develop new treatments.

New treatments for bone defects can currently only be studied to a limited extent in laboratory culture systems. In addition to such laboratory research, animal studies are therefore also necessary to test whether a therapy can actually restore bone before it can be evaluated in patients. Thanks to Dutch and European legislation, animal welfare is carefully monitored throughout this process.

Advancing medical healthcare inherently implicates both laboratory and animal experimentation, but with cautious considerations on return rate, (unnecessary) animal discomfort, and speed (of the translational process).

Our research aims to improve vaccines so that they can efficiently activate the immune system to fight cancer. We use both New Approach Methodologies (NAMs) and animal models to answer specific research questions. We always strive to carefully assess which method is best suited for each research question, and we believe that both approaches are valuable and necessary.

The immune system is highly complex and influenced by many factors throughout the body. Developing immune-competent New Approach Methodologies (NAMs) is therefore important for studying immune function. However, these methods cannot yet fully replicate how the immune system operates within a living organism. As a result, animal studies will remain necessary.

Nearly 1.8 million people living in the Netherlands have a cardiovascular disease, highlighting the importance of understanding these conditions better. As a researcher, I study how these diseases develop and which processes in the body contribute to them. Whenever possible, I use patient samples and cell-based models. However, these approaches are not always sufficient. To investigate the complex interactions that occur within a living organism, animal research remains necessary for the time being.

My group studies the side effects of radiotherapy, which can cause damage to healthy tissues. To do so, we use a range of experimental models, including cell lines, organoids, and tissue slices derived from surplus patient tissue. These models allow us to answer many important research questions. However, because radiotherapy-induced side effects can affect the physiology of the entire organism, it remains important at certain stages of the research process to use animal models to fully understand these complex responses.

Using advanced software, I help researchers analyze primate DNA more accurately and efficiently. This provides deeper insights into for example the immune system and helps improve study set-ups. In doing so, our work contributes to the 3Rs principles—Replacement, Reduction, and Refinement of animal research. In addition, we make our data and tools as openly available as possible, enabling other researchers to use and build upon our results.

Together with my team, I investigate the biological processes underlying diseases such as long COVID and neurodegenerative disorders. Using advanced in vitro models, we are able to replicate key aspects of these diseases. While these models provide important information, they cannot yet fully capture the complexity of a living organism. Animal models therefore remain necessary in some cases to better understand disease processes, including the role of the immune system, and to develop new treatments.

We all want safe and effective vaccines against infectious diseases for ourselves, our children, and older members of our communities. The effectiveness—and especially the safety—of vaccines can only be fully evaluated in a complete living organism. For this reason, I use animal models as an essential part of vaccine research.

Post-viral conditions such as long COVID affect millions of people worldwide. In our laboratory, we develop and use mini-gut models to investigate how viral infections can lead to persistent gastrointestinal symptoms. These models are used alongside animal research and help us better understand the underlying causes of intestinal dysfunction. This knowledge is essential for developing improved diagnostic tools and more effective treatments for patients.

In our research, we are continuously developing more ethical and innovative alternatives to animal experiments. I believe in a future where few, or perhaps no, animals will be needed for scientific research. At the same time, current alternative methods are not yet able to fully replicate the complexity of a living organism. Therefore, scientific progress today depends on a combination of approaches that complement and strengthen each other.

I develop 3D lymph node culture models as an alternative to replace animal models. For me, animal-free research is important because it is ethically responsible, more closely reflects human biology, and stimulates innovation in biomedical research.

I think there needs to be a shift in the idea that we need animal models, and that in vitro models are worse. This is just not the case, in many cases in vitro models can be better

The animal experiments conducted at the NKI represent the tip of an imaginary pyramid. In vitro experiments form the broad foundation. Advanced and innovative research methods, such as 3D cultures with organoids and patient-derived cell cultures, are located in the narrowing middle section of the pyramid. Only when no other method can adequately address the research question do we use laboratory animals. Our credo is therefore: alternatives whenever possible—laboratory animals when necessary.

Fundamental mechanistic knowledge on how the brain functions can only be obtained from carefully designed animal experiments. This fundamental knowledge is crucial for developing and testing treatments of cognitive, sensory, and motor deficits and of neurodegenerative diseases.

We have limited means in humans and artificial models to study how brains store memories, enable learning, and support behaviors, such as vocal interactions. Through animal research, we are able to expand our knowledge about how the brain works, how we learn, speak and interact.

Translational research is founded upon and critically dependent on insights from fundamental research involving animal models (as well as human studies). Our understanding of the fundamental biological mechanisms that govern life—including the complex interactions among genes, organ systems such as the nervous and immune systems, and environmental factors—remains incomplete. Animal research helps elucidating the functions of molecules, tissues, and organs, and provides a foundation for the translation of this knowledge into effective therapeutic interventions and medicines.

Biomedical research will continue to benefit from a combination of experimental approaches spanning the spectrum from individual molecules to the human organism as a whole. Laboratory animals—from small to large species—constitute indispensable links in this chain and contribute significantly to our understanding of both fundamental biological mechanisms and disease-related processes.

We investigate various aspects of severe lung abnormalities that arise during pregnancy. Despite the availability of alternative methods, the use of animal models remains important for understanding the development and growth of complex organs such as the lung. The interactions between different tissues within a living organism cannot yet be fully replicated in experimental models. However, by using NAMs, such as organoids and organ-on-chip systems, we are able to conduct more targeted and effective research, thereby also contributing to the principles of the 3Rs.

Our team aims to understand brain development and to gain insight into the underlying problems in congenital abnormalities and other neurological disorders (e.g., Parkinson’s disease). We primarily use cell-based systems where possible, but in some cases the full complexity of the brain is required to obtain meaningful insight into potential treatments. In those situations, we still rely on animal studies, which in such cases are considered scientifically and socially necessary.

As a computational neuroscientist, I strive to minimize the use of animals in research. However, there are fundamental questions that cannot be answered through simulation alone, because only living tissue—and often animal models, particularly in the study of psychiatric disorders—can help us understand the complexity required for developing treatments for mental illnesses.

Research involving laboratory animals should not be conducted lightly, and it isn't. For the time being, this type of research remains an essential component of making progress in the treatment of a wide range of diseases.

For my research, I make a carefully considered selection of the biomedical models that best address the identified scientific questions. Where necessary, animal studies form an integral part of the research, as they provide unique insights into complex biological processes within a complete living organism. At the same time, the principles of Replacement, Reduction, and Refinement (the 3Rs) serve as a guiding framework, and we continuously strive to further minimize the use of laboratory animals wherever possible.

As a computer scientist, I would very much like computer simulations to be capable of replacing animal experiments today. Unfortunately, this is not yet the case, nor is it likely to be in the foreseeable future. If we are to understand the brain and develop effective treatments for neurological disorders that affect us and our loved ones, we must combine animal research with non-animal approaches, such as computational models and organoid systems.

Animal research will remain essential for the foreseeable future to advance our understanding of brain function and to develop effective treatments for brain disorders.

I endorse the necessity to perform high-quality research in animals to understand complex disease processes and develop new therapies, e.g., by intravital microscopy. In parallel, my research aims to build better, in-vivo inspired 3D models. We have no alternative to animal studies in order to validate better 3D in vitro models. 3D model development should come with in vivo validation, and in vivo research in animals should come with parallel studies to build adequate in vitro models.

As a translational immunologist, I investigate how immune responses against self-proteins contribute to disease, with the aim of improving both diagnosis and treatment. We integrate patient-derived material, in vitro cell culture systems, and animal models to elucidate underlying disease mechanisms and translate these findings into clinical application. While New Approach Methodologies (NAMs) contribute to reducing the reliance on animal experimentation, animal models remain necessary for the foreseeable future to validate findings within the complexity of an intact living organism.

Patients can experience a wide range of side effects from therapy, such as fatigue, weight loss, and hair loss. These effects can be devastating for patients. If you want to understand how anticancer drugs cause these side effects and find ways to prevent or reduce them, there is no alternative but to study this in animal models. Through this research, we have developed variants of chemotherapeutic drugs that no longer cause these side effects. Animal experiments were essential to achieving this.

For many years, I have been conducting research into the consequences and treatment of high blood pressure. This condition has far-reaching effects on numerous organs and can only be properly studied in an intact animal model. The heart, blood vessels, as well as the kidneys, adrenal glands, and brain all play a role. They influence one another through the nervous system and various hormonal systems, and understanding their interaction requires a complete living organism.

Dysregulated lipid metabolism plays a key role in numerous diseases, including fatty liver disease and cardiovascular disease, both highly prevalent and major causes of mortality. By using genetically modified mice, we are gaining a deeper understanding of how lipid metabolism contributes to these conditions, in part because lipid metabolic pathways are highly comparable between mice and humans. Animal studies therefore remain essential for unraveling the complex mechanisms underlying these diseases and ultimately for the development of effective therapeutic strategies.

We investigate how the liver and intestines cooperate in maintaining the body's energy balance and how it becomes disrupted in metabolic diseases. While our mechanistic research is conducted using intestinal and liver organoids, animal studies remain essential for understanding the complex interplay between organs in regulating metabolism. I believe it is important to continue pursuing the refinement and replacement of animal experiments wherever possible; however, the complete phase-out of animal research in academic science is not currently feasible.

Animal studies will remain indispensable for understanding the complex interactions between different cell types and tissues that play a critical role in the development and treatment of a wide range of diseases. Cancer, and the development of effective anticancer therapies, is a prime example. Even the most advanced ex vivo systems can only partially replicate the intricate cellular and tissue-level interactions that occur within a living organism.

As a researcher who studies cancer metastasis, I find it extremely important that experiments involving animal models continue. At the moment, not every biological process is possible to reconstruct in vitro or in computational models. To transition to animal-free research, it is important to study complex biological systems in their native state, so that the follow-up models represent animal and, eventually, human organism in the most comprehensive way.

When people think of animal experimentation, they often associate it with biomedical and toxicological research conducted in laboratories. However, a substantial amount of animal research also takes place in the field and involves wild animal populations. These studies, too, fall within the scope of animal experimentation. Our field research on fish, for example, involves tagging individuals with transmitters to monitor their movements and behavior, with the ultimate goal of conserving and enhancing fish populations. By highlighting this aspect of animal research, we present a different perspective on animal experimentation—one that is generally received with considerable enthusiasm by the public.

The hormone cortisol is involved in a wide range of diseases, including various forms of cancer, neurodegenerative disorders, liver diseases, and many others. We develop methods for treatment of these conditions based on cortisol’s biological actions. Many of our insights originate from animal research. In many cases, rigorous testing of our hypotheses and therapeutic approaches can only be achieved in animal models, as current alternatives remain insufficient to accurately predict the body's integrated physiological response. For this reason, animal research continues to be an essential component of our work.

My research focuses on the earliest stages of brain development and on understanding what goes wrong in rare genetic disorders. Patient-derived stem cells and brain organoids are an enormous source of information, but they cannot teach us how different brain regions interact during development. To see the whole picture, we also study the developing mouse brain. Every piece of the puzzle matters!

Animal research ensures that procedures are carried out by individuals with demonstrated knowledge and expertise under carefully controlled conditions, with both internal and external oversight in place. This level of regulation and supervision does not necessarily apply to procedures that fall outside the scope of animal experimentation legislation. Animal studies can also contribute to improvements in animal health care and animal welfare. Examples include research into the transmission and prevention of infectious diseases, as well as studies aimed at understanding natural animal behavior.

As a theoretical neuroscientist, my work is highly dependent on the collection and availability of animal data. At the moment most of our understanding of brain functioning, in health and disease, comes from performing experiments on animals. This is true also when considering mathematical modelling of neural networks, which finds its validation and direction from a constant interaction wirh experimantal data, and that would be impossible without it.

Research with and without animal models go hand in hand. Animal studies remain essential for understanding how diseases develop and for creating effective treatments, because the complexity of a living organism cannot yet be fully reproduced in cell-based systems. That is why the responsible and ethical use of laboratory animals continues to play a vital role in biomedical research.

The diagnosis and treatment of patients with head and neck cancer can and should be further improved. For example, we currently have no effective method to treat precancerous lesions in the mucosal lining of the mouth and throat. While a great deal of research can be conducted using 2D and 3D cell culture models, potential new treatments ultimately need to be tested in animal models before proceeding to clinical studies in patients. At present, this essential step in the research process cannot be omitted.

Understanding how the brain controls body weight and blood glucose requires studying the intricate connections between reward circuits, metabolic centers, and the autonomic nervous system. These complex networks cannot yet be investigated directly in humans. While we actively support and adopt alternative methods whenever possible, animal research remains essential for driving progress in diabetes and obesity research and ultimately improving patient care.

We perform animal experiments to study how animals use their environment, whether then can pass human-made obstacles, and if they are healthy. We do this using small tracking devices or by taking a small tissue sample, after which the animals continue their lives in the wild. The knowledge that gives us is important for improving their habitats and recovery of populations that are under pressure.

To study, prevent, and treat a complex disease such as cancer—whose development and progression are strongly influenced by lifestyle factors—it is necessary to investigate biological processes within a complete organ or living organism. At present, there is no alternative that can fully replace animal models for studying cancer and advancing new approaches to help cancer patients.

Within our research group, we use innovative models, such as stem cell models, to better understand metabolism and cardiovascular diseases. However, these models are still unable to fully replicate all the complex processes that occur in the body. Therefore, animal research remains necessary for the time being to develop new treatments safely and effectively.

Hormones play a crucial role in virtually all processes in our body, ranging from energy metabolism to growth, sleep, and reproduction. Disturbances in hormone levels underlie common diseases such as obesity and diabetes, as well as more than 400 rare disorders. Before testing new medicines in humans, we need to ensure that they are safe and identify the most promising therapeutic strategies. To achieve this, we use animal studies.

Radiotherapy improves the health and quality of life of people with cancer, but it can also cause damage to surrounding tissues and organs, leading to side effects. While alternatives to animal testing provide valuable insights, they are not yet able to adequately replicate the complexity of a living organism. Therefore, animal studies remain necessary in certain cases to investigate effects at the whole-organism level and to improve treatments.

Cardiovascular diseases have an impact on human health. These conditions arise from complex interactions between the heart and the rest of the body. To understand these processes, the heart must be studied in its natural environment—the living body. This cannot yet be fully replicated in humans or in isolated human heart cells grown in the lab. Therefore, animal research remains necessary to improve our understanding of cardiovascular disease and to develop better treatments for patients.

As a neuroscientist, I study how genetic changes influence brain development and behavior. To understand these complex processes, I sometimes need animal models. While I look forward to the continued development of animal-free alternatives, these methods cannot yet fully replicate the interactions between genes, brain circuits, and behavior. Therefore, both approaches remain necessary for the time being to advance research into neurodevelopmental disorders.

Neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease develop gradually within a highly complex system involving many types of neurons, support cells, blood vessels, and extracellular protein networks. Even the most advanced cell culture systems that incorporate multiple brain regions can only model a fraction of this complexity. Therefore, research using animal models remains essential for understanding these diseases and for developing and testing new treatments.

Results obtained from cell-based or computer models cannot usually be tested directly on humans. Animal research serves as an important intermediate step.

The autoimmune disease rheumatoid arthritis primarily manifests in the joints, but it arises from complex interactions between multiple types of immune and non-immune cells that are activated and regulated at different sites throughout the body. In addition, autoantibodies circulate through the bloodstream and contribute to disease development and progression. Understanding how to restore balance within the immune system to effectively treat diseases like rheumatoid arthritis requires not only in vitro studies, but also investigation of the immune system as an integrated whole, using animal models.

Disease rarely originates in a single cell. In diabetes and vascular ageing, blood vessels, muscles, the heart, and the immune system are in constant communication with one another. Animal models help us understand these complex interactions within a living organism. We combine the knowledge gained from animal studies with human research and animal-free models, allowing us to better understand how disease develops and where therapeutic interventions may be most effective.

Complex in vitro models represent a promising pathway toward better and more relevant scientific research. Although these models are still at a relatively early stage of development—particularly when compared with the decades of development behind animal models—it is crucial that we continue to invest in their further development and validation. Over time, this will increase their applicability and reduce the need for animal experiments.

We conduct animal research because our goal is to better understand the species itself. In our research group, we study fish, for example to learn more about how they migrate from the sea to our rivers. We also investigate how farmed fish can be cared for in the best possible way to promote their health and welfare. We can obtain a lot of valuable information through collecting a small blood sample after implanting a tracking tag, under anesthesia.

To understand how the brain responds to cancer and its treatment, we still rely on animal models. Although innovative alternatives such as brain organoids are developing rapidly, they cannot yet fully replicate the complexity of the living brain. As a result, animal studies remain essential for linking molecular and cellular mechanisms to functional outcomes and, ultimately, to clinical applications.

We study the neurobiological milestones underlying memory development and how the environment shapes cognitive maturation. Using translationally relevant behavioural tests in rodent pups, we relate memory development to the maturation of neuronal processes and early life experiences. The level of detail with which we study neuronal and behavioural maturation require the use of experimental animals. The insight we gain through this research will help identify neuronal and environmental factors that influence cognitive development.

As a reserach institute, we study wild mammals (in their habitat). Many ecological, legally required, and societal questions can only be answered through the use of transmitters (internal/external), the marking of mammals, etc. All of these procedures fall under the Dutch Animal Experiments Act. There are no alternatives, because the research concerns species X, in area Y, during season or year Z. This is extremely important research for the conservation of our biodiversity.

We study the molecules that play a role in the formation and modification of connections in the brain. We aim to unravel the signalling pathways that are important for the learning and adaptive capacity of the brain. The use of brain tissue from laboratory animals is necessary for this research. The aim of our research is to gain a better understanding of how the brain works, and it contributes to the development of treatments for brain diseases.

My company is a supplier to the biomedical research community. Our customers make a careful, case-by-case decision on whether a research question should be addressed using an animal experiment or a NAM. When an animal experiment is required, we provide equipment and software to automate behavioural testing. Our tools are designed to minimise disturbance to the animals during testing while maximising data output. In this way, we contribute to the refinement and reduction of animal experiments.

A balanced lethal system is an exceptional genetic system in which certain chromosome combinations are lethal, while others are essential for survival. Using crested newts, I investigate how such a system evolved millions of years ago and which genes are involved in the characteristic embryonic mortality. Because balanced lethal systems are extremely rare, this research provides a unique opportunity to answer fundamental questions about evolution and gene function.

In vitro cell models are highly suitable for addressing fundamental cell biological questions. However, when it comes to the complex interactions between cells within an intact organism—and how these processes are disrupted in disease, such as the memory processes we study—an animal model remains indispensable.

Immunotherapy requires an understanding of complex cellular interactions that NAMs, such as organoids, can only partially replicate. Animal models remain indispensable for studying the full dynamics of the immune system, including circulating immune cells and communication between organs, within a living organism. Until NAMs are able to model the full complexity of the immune system, we use both complementary approaches in our research.

We provide knowledge about conditions that promote health and positive experiences in farm animals. Understanding how resilience and welfare, including affective states, can be assessed and improved is an important part of our work. We increasingly employ non-invasive methods to collect physiological samples. However, given that we combine behavioural, cognitive and physiological measurements at the individual and group level, animal studies are essential to address knowledge gaps in our field.

My team conducts research on neuromuscular diseases such as myasthenia gravis, which is characterized by severe skeletal muscle weakness caused by antibodies of the immune system that attack the body's own tissues. Such a complex disease cannot be adequately captured using cell models alone, because it affects skeletal muscles throughout the body to varying degrees. To better understand the disease and to test new therapies, we sometimes use animal models that replicate the disease observed in patients. Whenever possible, we choose alternative methods, and therefore we are developing 3D muscle models and 3D immune cell models in culture dishes to study the disease more effectively and ultimately help patients.

Preventing influenza deaths is an ongoing struggle, especially in vulnerable populations. By doing my research, I want to contribute to a better understanding of influenza infections in humans & help develop more effective vaccinations for a future free of influenza.

To better understand health and disease, we use a range of research methods at UMCG, from computer models and organs-on-a-chip to animal research and clinical studies. Wherever possible, we choose alternative methods and limit the use of laboratory animals in accordance with the principles of the 3Rs. Combining approaches is what enables us to develop new strategies for prevention, diagnosis, and treatment for patients—and to fulfil our mission: More healthy years for everyone.

We are proud of the work we do in our laboratory animal facility. Behind every research project involving laboratory animals is a dedicated team of animal caretakers, biotechnicians, veterinarians, researchers, and support staff who are committed every day to scientific excellence and animal welfare. Together, we ensure that research is conducted responsibly and with the utmost care, while continuously advancing the principles of the 3Rs. In doing so, we support research that contributes to healthier lives and more years of good health for everyone.

We study the mechanisms underlying brain disorders, including both psychiatric and neurological conditions. Whenever possible, we do this without using animal models. However, it remains important to understand how changes in the brain are linked to changes in behavior. For this type of research, animal models are indispensable. I am committed to optimally integrating research methods with and without animal models, so that the number of animals needed can be reduced as much as possible.

Animal research remains important because only a living organism can adequately capture the complexity of disease processes. In vitro models and organ-on-a-chip systems are valuable tools, but they do not yet fully replicate the systemic dysregulation seen in intensive care patients, where inflammation, circulation, vascular function, and multiple organ systems are tightly interconnected.

For vaccine research, there is currently no in vitro model available that adequately replicates the complexity of the immune system. Therefore, animal research—specifically studies of the immune response induced by vaccines—remains crucial in our ongoing fight against viruses.

Through research, we improve the health of the population. To achieve this, our researchers use a variety of models. They continuously work to optimise the effectiveness and minimise any adverse effects on humans, animals, and the environment of the in silico, in vitro, and in vivo models they employ. Erasmus MC only uses animal experiments when necessary (for example, when it is essential to study blood flow, neuronal function, or immune responses) and actively promotes alternative methods.

Most medical advances, from for example drug compounds to surgical techniques, depend on animal research to go from theory to safe clinical use. Despite progress in animal-free methods, they cannot replace whole-organism biology, as the complexity of processes such as blood flow in the vascular system, immune responses or organ interactions cannot be fully replicated in cell cultures or computer models, making animal research indispensable.

Various neurological disorders remain untreatable because we still have an incomplete understanding of the underlying disease mechanisms. My research focuses on how different physiological systems—including the cardiovascular system, the nervous system, and the glymphatic system—interact with one another, and how these interactions are altered in brain diseases. Animal models are essential for this work because current alternative methods cannot adequately replicate the complexity of these interconnected systems within a living organism.

My research focuses on understanding how the brain controls behavior. Many of the questions we investigate can only be answered through animal research. The findings we generate are important for advancing fundamental scientific knowledge, but also for improving our understanding of a wide range of neurological disorders. These disorders impose a significant burden on patients and society, yet many remain untreatable. Animal research continues to be essential for making progress toward better understanding and future treatments.

Stress-related disorders, such as PTSD and depression, have a profound impact on both individuals and society. Because the underlying neurobiological mechanisms are still not fully understood, current treatments are often suboptimal. My research focuses on the effects of stress on the brain to improve our understanding of these disorders and to support the development of more effective future treatments. Animal models are essential in this work, as they provide crucial insights into the brain processes that contribute to the symptoms of these conditions.

I believe it is important to communicate clearly and transparently about the circumstances in which animal research remains essential, as well as the measures scientists take to ensure and continuously improve animal welfare.

My research focuses on developing and evaluating Positron Emission Tomography (PET) imaging tracers for disease diagnosis and accelerate drug discovery. Translating these complex biochemical probes from the lab to human patients safely and effectively requires animal research. Living animal models provide the essential, intact physiological systems needed to track tracer kinetics, biodistribution, and efficacy in real-time, insights that non-animal alternatives cannot replicate or predict.

We use rodent models to study how the brain controls movement and we also use non-animal approaches. In my view, these methods are not in competition but are complementary ways of understanding the brain. Some questions about neural mechanisms cannot yet be answered without animal research, while others can and should be addressed with non-animal methods. To develop better treatments, we need to combine these approaches responsibly and commit to reducing animal use wherever possible.

Viruses have a major impact on the health of both humans and animals. New insights into disease processes, transmission routes, and immune responses to viral infections can lead to solutions that reduce this impact. Where possible, we use animal-free methods. However, laboratory animals remain necessary for research that cannot be conducted in a single cell or organ. We use laboratory animals as little as possible, but as much as necessary. In doing so, we adhere to the 3Rs principles (Replacement, Reduction, and Refinement).

Staying healthy is important to all of us. Animal research is an indispensable part of the broad range of research methods that scientists use to advance health: patient studies, human-derived materials, cell culture, and organs-on-chips the available methods continue to expand, but animal models remain essential for studying complex interactions between organs. The Animal Research Facility (CDL) is partner in quality of science, education and animal welfare animals is a top priority. Through this work, we make a significant contribution to improving health by advancing scientific knowledge, training physicians, and supporting the development of new medicines and diagnostic methods.