Advances in CRISPR Disease Modeling: Cells, Organoids, Animals, and More
Disease modeling helps us understand disease and create therapies. This blog covers types of disease models, the impact of CRISPR, current challenges, and trends.
Disease modeling is crucial in biomedical research, helping scientists to understand diseases and formulate curative therapies. The last decade has seen significant advances in disease modeling, largely owing to CRISPR gene editing technology, which has made disease models more accurate than ever. But the first half of 2023 saw major developments in disease modeling that could mean we’re in for some even bigger changes in the coming years.
In this blog, we’re covering everything you need to know about these changes. We’ll cover the basics of disease modeling and why it's important, explain key types of disease models and the impact of CRISPR, then explore the problems in animal-based models of disease before we delve into the regulatory and industry changes in disease modeling, and how these changes will affect clinical development of new therapies.
What is Disease Modeling and Why is it Important
Disease models are biological systems, such as cells or animals, that mimic disease conditions for scientists to study in the laboratory. Disease modeling is critical for understanding diseases, identifying new therapeutic targets, and demonstrating the safety and efficacy of new disease treatments in preclinical studies. Let’s explore the different applications of disease models.
Understanding disease pathogenesis, symptoms, and progression
A key aspect of disease research is generating models that closely recapitulate disease conditions and progression. Disease models allow researchers to understand the molecular mechanisms and pathways that cause disease, how diseases develop (disease pathogenesis), and how they progress. For example, disease models allow us to study how particular mutations lead to disease pathogenesis, the symptoms of disease and their severity, and the progression of diseases over time.
Identifying therapeutic targets
Disease models are critical in drug discovery, helping to identify and validate new therapeutic targets. For example, a cancer cell line carrying a specific mutation can be used as an in vitro disease model to screen thousands of different small molecule drugs, allowing researchers to identify which of the drugs can halt cell growth or induce apoptosis.
Preclinical safety and efficacy studies
When a novel therapeutic target has been identified and validated, the next key step is to perform preclinical research, gathering data on the safety and efficacy of the therapy before it can be tested in human subjects. This is typically performed in vivo in animal disease models. It is critical that preclinical disease models are accurate so that the risk of failure or toxicity in human subjects is reduced as much as possible.
Understanding CRISPR Clinical Trials: Your Questions Answered
Types of Disease Models
There are several key types of disease models that vary in complexity, ranging from simple 2D cell cultures to advanced animal models. Let’s explore each type, and their advantages and limitations.
Cell-based models: 2D modeling
2D cell-based disease models can include patient-derived primary cells, immortalized cell lines, or stem cells such as induced pluripotent stem cells (iPSCs), that are grown in a monolayer in flasks or Petri dishes. These 2D cell cultures are important in disease modeling because they are simple, relatively reproducible, amenable to high-throughput screening, and can be produced at low costs depending on the cell type used. For these reasons, they are of particular relevance in early-stage drug discovery studies. However, they lack complexity and cells respond differently when they are grown in 2D cultures compared to 3D cultures or in vivo.
Spheroids and organoids: 3D structures
A step up from 2D cell culture, spheroids are self-assembling cell aggregates that form when culture conditions prevent the cells from attaching to a surface. Because they are a 3D model, there is an increase in cell-cell interactions and functionally differentiated layers. Spheroids can be generated via hanging drop, hydrogel, suspension, or other methods. They are frequently used in cancer modeling to mimic tumors, and can be generated either from cancer cell lines or primary tumor cells. The co-culture of stromal cells with cancer cells to create a heterotypic spheroid enables researchers to model the tumor microenvironment.
Another step up in complexity are organoids. Organoids use tissue-specific stem cells or iPSCs to create 3D models that are similar to miniaturized organs. The stem cells are provided with an extracellular matrix around which to grow, and growth factors that are necessary for development. They self-assemble, forming organ-specific cell types. Organoids have received significant attention in recent years and are becoming increasingly popular for disease modeling from genetic disorders to cancer, as well as in studies of developmental and evolutionary biology.
Organoids are small – between 100 microns and 2 millimeters, depending on the type – meaning that they are also suitable for high-throughput screening. They are much better at mimicking the biological complexities of real human organs than 2D cell culture models of disease. iPSC-derived organoids can now be produced for a range of organs, including the lung, brain, liver, kidney, stomach, gut, pancreas, and thyroid; both healthy organ systems and tumor-derived organoids can be used. Tissue-specific adult stem cell-derived organoids are also available for many organs.
Organ-on-a-chip: single and multi-organ systems
The most complex and promising in vitro disease models are chip organs, which can be either single or multi-organ systems. They are essentially a combination of cell culture and microfluidics technologies, designed to mimic the complex physiological conditions of organs and, in the case of multi-organ chips, the interactions between organs.
Recommended by LinkedIn
Unlike less complex models, organ chips can recreate key physiological processes, such as breathing, blood flow, and peristalsis. Organ chip pioneers have even developed chips that replicate skin, bone marrow, and the blood-brain barrier, the latter of which has historically been one of the most challenging human systems to model. While the true potential of organ chips has yet to be fully explored, they have already been shown to be valid predictive models of drug toxicity. By using cells taken directly from patients, organ chip systems can be developed as highly personalized disease models to determine which therapeutic options may be the most effective for each individual.
Disease modeling in vivo with animals
There are many in vivo disease models, the most common of which for preclinical research is the mouse. If a novel therapy addresses an unmet clinical need, validation of safety and efficacy in mice or another small animal model is often sufficient. However, some preclinical studies require further testing in larger animals, such as pigs or non-human primates (NHPs); this is often the case if the therapy is targeting specific organs such as the brain or the heart.
CRISPR Conversation: Laura Lambert Uses CRISPR to Create Animal Models
Problems in Animal-Based Disease Modeling
One of the key issues in animal-based disease models is their lack of accuracy, which leads to significant setbacks in the clinical translation of new drug products. If a drug has been approved to begin testing in humans, that means that the safety and efficacy of the product have been proven in animal models. Yet almost 90% of all new drugs that are successfully tested in animals fail when they reach human trials, often with adverse patient outcomes.
Animals such as mice cannot accurately recapitulate the complex molecular underpinnings, disease phenotypes, or progression seen in human subjects. Testing in larger animals, such as NHPs, carries an ethical burden as well as high costs and does not always ensure the therapy will succeed in human trials. Additionally, concerns have been raised about the validity of data generated from lab animals because of the artificial conditions in which they are kept, as well as ethical issues associated with their use.
The Role of CRISPR in Disease Modeling
The impact of CRISPR-Cas9 genome engineering in disease modeling cannot be understated. Because many diseases are caused by genetic mutations, disease modeling and genetic engineering go hand-in-hand. Many disease areas suffered from a lack of accurate models until the advent of CRISPR technology; compared to previous genome engineering technologies, CRISPR is simple, efficient, and low-cost. It can be used to create complex edits in almost any cell type, including primary human cells and iPSCs– which have traditionally been resistant to genetic manipulation – as well as whole animals.
CRISPR has now been adopted in labs around the world to create precision models of genetic diseases and cancer in cells, organoids, and animals, accelerating the clinical development of new therapies. For example, CRISPR editing can be used to establish cause-effect relationships between genetic mutations and disease phenotypes, to screen for new therapeutic targets in high-throughput assays, and to create humanized mice, in which the mouse version of a gene is replaced with the human equivalent for more accurate disease modeling.
Many proof-of-concept studies now use a complementary dual-CRISPR approach: first to induce pathogenic mutations in healthy donor-derived cells to prove causality and model disease pathogenesis, and then conversely to correct or otherwise edit the mutation in patient-derived cells to demonstrate the potential of a gene or cell therapy approach.
Regulatory Changes: FDA No Longer Requires Animal Testing
At the beginning of 2023, the FDA made waves in the scientific community by announcing that it would no longer require all new drugs to be tested in animal models before commencing human trials. This news was welcomed both by animal rights activists and the growing number of scientists who have voiced concerns about the accuracy of pre-clinical data generated from animal models. The US federal budget echoed the announcement with USD 5 million in funding for the FDA’s program to reduce animal testing by encouraging industry to invest in alternative methods.
While significant, this regulatory change does not mean that researchers will be abandoning animal research altogether – at least, not yet. Rather, this is the beginning of a shift toward reducing and refining the use of animals and investing in advanced in vitro models such as organoids and organ chips. The announcement has already caused significant ripples across the cell and gene therapy industry. In May 2023, Roche announced the launch of its own Institute of Human Biology - a research group that will create more accurate human model systems, such as organoids, in order to accelerate clinical development and minimize animal testing.
How Advanced Disease Models Can Create Safer Therapies
The rapid rise of CRISPR technology, combined with other advances in biomedical science, means we have entered a new era in disease modeling and treatment. We are now able to create more accurate disease models than ever before, enabling the study of almost any mutation. Even complex, multifactorial diseases can now be studied thanks to the ease of CRISPR engineering in cells and animals.
The producers and early adopters of organ chip systems have hailed them as the most promising alternatives to animal models. Combining CRISPR edits with advanced in vitro disease models, such as organoids and organ chips, allow researchers to create personalized models that can both accurately recapitulate disease and precisely model the effects of different treatments on the individual. This could accelerate the clinical development process for new drugs as well as minimize the risk of toxicity and other adverse events in human trials.
It remains unclear how rapidly change will occur, but the recent announcements and initiatives in the disease modeling space certainly suggest we’re on the cusp of a significant period of growth in the industry. Although many scientists say animal models will never be completely eliminated – in fact, it can be argued that CRISPR editing has made animal models more relevant than ever – we can expect to see organoids and organ chips being brought to the fore of preclinical research in the coming years.
We hope this blog helps you get up-to-date with disease modeling, problems with animal testing, regulatory changes, and the future of precision disease modeling with CRISPR. With CRISPR disease models, personalized medicine is within reach, and CRISPR cures are already changing the lives of patients. Need more insights on clinical development and regulatory trends? Subscribe to The Bench for regular updates. Do you want to use CRISPR disease modeling in your research? Schedule a free consultation with one of our genome engineering experts!
Dr. Rebecca Roberts