Kiave Yune Ho Wang Yin, PhD, Chief Business Officer at TransCure bioServices explores how humanized mouse models can be used to develop more relevant preclinical studies for IBD treatments and ultimately increase the likelihood of a treatment’s success in clinical trials.
Inflammatory bowel diseases (IBDs), including Crohn’s disease and ulcerative colitis (UC), are a global health concern that significantly impact the quality of life (QOL) of up to 10 million people.1 Characterised by chronic intestinal inflammation, IBDs manifest through severe symptoms such as persistent diarrhea, abdominal pain, and fatigue.
Conventional treatments for IBD, such as corticosteroids and immunomodulators, aim to control disease symptoms. However, a substantial number of patients either do not respond or lose response over time to standard therapies such as these. There is an urgent need, therefore, for new treatment strategies that can help improve QOL for the millions of affected individuals.
Unfortunately, the path to successful new treatments is fraught with obstacles, and the rate of new product approval remains low — despite a large pipeline of potential therapies. Notably, many potential treatments fall short at the clinical trials stage, even when they demonstrate promising safety and efficacy profiles during pre-clinical studies.
One of the most significant factors that indicates the success of a potential treatment in clinical trials is the preclinical model used. Currently, many models struggle to provide safety and efficacy data that accurately predicts how a treatment is likely to work in the human population. But more human-relevant models, such as humanized mouse models, can provide deeper insights into treatment efficacy and safety, thereby enabling data-driven decision making.
Why use a humanized mouse model for preclinical studies?
In the CD34+ humanized immune system mouse model, the mice reconstitute all human immune targets, providing a platform where researchers can observe and analyse the intricate interactions between the various immune cell constituents. The models offer stable humanization throughout the animal’s lifetime, and also avoid graft-versus-host disease (GvHD) onset — an issue common in other mouse models. By avoiding GvHD, animal welfare is increased, and variabilities in research data are reduced.
A distinguishing aspect of CD34+ humanized mouse models is that mice can undergo hydrodynamic boosting to increase their myeloid cell levels. Myeloid cells are key drivers of IBD, and so boosting them enables researchers to study IBD progression and responses to therapy under conditions that more closely mirror those in human patients. Certain key growth factors and cytokines such as Interleukin-3 (IL-3), Interleukin-4 (IL-4), Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF), and Fms-like tyrosine kinase 3 ligand (FLT3L) can all be boosted, depending on the condition studied.
Deeper insights into the immune system
Since many novel treatments for conditions such as IBD target pro-inflammatory pathways, a deeper understanding of the immune system during preclinical studies is imperative. As humanized immune system mouse models recapitulate the human immune system, they are an ideal choice for a preclinical model, yielding richer efficacy and safety data.
Three key considerations for a successful preclinical study
While humanized mouse models show great potential in IBD preclinical studies, you must design your experiment carefully to get the insights you need. There are three considerations that allow researchers to leverage these models to their full potential: the disease induction method, the design of the experimental protocol and its corresponding readouts, and the approach to scoring the disease progression and severity. We explore these in more detail below.
Disease induction method
Crohn’s and UC manifest in the body in different ways. Crohn’s, for example, can affect any part of the gastrointestinal (GI) tract, although it most commonly affects the small intestine near to the colon. UC, on the other hand, affects the large intestine and the rectum. Therefore, to ensure the highest degree of physiological relevance from your mouse model, you must induce the disease in a way that closely represents its presentation in the human body.
Two common chemicals can induce UC and Crohn’s disease in a mouse model:
- Dextran sodium sulfate (DSS) for UC: DSS destroys the mucus layer and interrupts the epithelial barrier integrity, leading to inflammation. Additionally, DSS induces the secretion of pro-inflammatory cytokines such as IL-6 or TNF-alpha, similar to that seen in humans with UC.
- 2,4,6-trinitrobenzene sulfonic acid (TNBS) for Crohn’s disease: TNBS, when mixed with ethanol and instilled intra-rectally, disrupts the mucosal barrier and allows TNBS to bind to proteins in the colon. Subsequently, there is excessive secretion of IL-12 and other pro-inflammatory cytokines, effectively simulating human Crohn’s disease.
Protocol design
As mentioned earlier, the protocol must accurately induce UC or Crohn’s disease as they manifest in humans. Take, for example, the design considerations needed for both acute and chronic forms of UC. For acute UC, mice undergo DSS administration in their drinking water for a span of seven days, followed by a washout period where they receive only normal water, until day 13. In contrast, for chronic UC, researchers reflect disease severity by exposing the mice to 2 to 3 DSS cycles, alternating every five or six days between DSS administration and the washout period.
Acute Crohn’s disease presents a different case entirely. Here, a single intrarectal instillation of TNBS induces the disease in the correct part of the small intestine, followed by a waiting period of a few days for the disease to manifest. Typically, the protocol is short, only taking around seven days (Figure 1).
Figure 1: Protocol timelines for acute UC (top), chronic UC (center), and acute Crohn’s disease (bottom).
Disease scoring approach
Assessing the disease severity and progression in preclinical studies is central to understanding potential treatment effects. Three key approaches are used:
- Clinical scoring of factors including body weight, diarrhea presence/severity, any noticeable bleeding, and mortality
- Histopathology, or colon collection, to identify the precise pathological changes that occurred during the disease
- Endoscopy to visually assess the state of the mucosa and identify inflammation onset and severity
For ulcerative colitis (UC), clinical symptoms are rated on a scale from 0 to 4, as shown in Table 1.2 A cumulative clinical score of the measurements is calculated and scored out of 12, enabling researchers to monitor the extent of inflammation, tissue damage, and mononuclear immune cell infiltration.
Figure 1: Protocol timelines for acute UC (top), chronic UC (center), and acute Crohn’s disease (bottom).Disease scoring approach
Assessing the disease severity and progression in preclinical studies is central to understanding potential treatment effects. Three key approaches are used:
- Clinical scoring of factors including body weight, diarrhea presence/severity, any noticeable bleeding, and mortality
- Histopathology, or colon collection, to identify the precise pathological changes that occurred during the disease
- Endoscopy to visually assess the state of the mucosa and identify inflammation onset and severity
For ulcerative colitis (UC), clinical symptoms are rated on a scale from 0 to 4, as shown in Table 1.2 A cumulative clinical score of the measurements is calculated and scored out of 12, enabling researchers to monitor the extent of inflammation, tissue damage, and mononuclear immune cell infiltration.
Table 1: Clinical UC scales and scores.2
Endoscopy readouts form part of the Murine Endoscopic Index of Colitis Severity (MEICS), as shown in Table 2.2 Such readouts offer an early and accurate visual portrayal of the colon compared to clinical scoring alone.
Table 2: Endoscopy UC scales and scores, also known as MEICS.3
The power of the preclinical model
The strength of humanized mouse models in preclinical IBD is illustrated by studies demonstrating successful disease induction and evaluating the efficacy of two well-known treatments: adalimumab for UC and ustekinumab for Crohn’s disease.
Adalimumab for UC
Adalimumab, a clinically approved drug, treats moderate to severe UC in adults and children over the age of five. However, the treatment cannot be taken when there is any kind of infection, and it only improves symptoms or causes remission in approximately 54% of patients,4 underlining the need for more effective therapies.
Adalimumab is an excellent reference drug for investigating preclinical model performance. In an internal study, humanized mice treated with DSS showed an increase in cumulative clinical score, signifying successful disease induction in this model. When these acute UC mice were subsequently treated with adalimumab, researchers observed reduction in the clinical score, as expected from the drug’s therapeutic effect. Similarly, in a chronic UC model, adalimumab reduced diarrhea and bleeding scores, and it improved overall survival.
Ustekinumab for Crohn’s disease
Ustekinumab is a treatment option for Crohn’s disease that is administered via intravenous or subcutaneous injection. Similar to adalimumab, not every patient responds to the treatment. Additionally, the treatment can negatively impact the immune system, potentially making it more difficult for patients to fight off infections.
In another internal study, TNBS treatment in humanized mice successfully induced strong clinical scores, and resulted in noticeable tissue damage. Ustekinumab treatment led to a significant decrease in the clinical scoring for mice with acute Crohn’s disease and reduced the endoscopy score on day seven.
Taken together, these benchmark studies demonstrate the success of both the DSS and TNBS disease induction protocols in humanized mice and confirm that humanized mice serve as suitable and highly informative models for assessing potential IBD treatments.
Unearth deeper insights from your IBD studies with humanized mice
Humanized mouse models have emerged as powerful tools for preclinical IBD research, offering unparalleled insights into the potential efficacy and safety of novel treatments. It is essential, however, to carefully consider your disease induction method, protocol design and readouts, and scoring approach to ensure the most relevant and robust data is gathered from your studies.
With a preclinical humanized model and robust study design for your IBD studies, you can ensure you progress only the most promising drug candidates towards clinical trials. Ultimately, such capabilities will better equip your organisation for rapid and effective treatment delivery to the millions of patients worldwide living with IBD.
References
[1] Ampersand (2022), IBD Statistics 2022: Crohn’s and Ulcerative Colitis. Available at: https://ampersandhealth.co.uk/myibdcare/resources/ibd-statistics-2022-crohns-and-ulcerative-colitis/ [2] Martin-Rodriguez O, Gauthier T, Bonnefoy F, Couturier M, Daoui A, Chagué C, Valmary-Degano S, Gay C, Saas P, Perruche S. Pro-resolving factors released by macrophages after ef-ferocytosis promote mucosal wound healing in inflammatory bowel disease. Front Immunol. 2021 Dec 22;12:754475. DOI: 10.3389/fimmu.2021.754475 [3] Becker C, Fantini MC, Wirtz S, Nikolaev A, Kiesslich R, Lehr HA, Galle PR, Neurath MF. In vivo imaging of colitis and colon cancer development in mice using high resolution chromoendos-copy. Gut. 2005 Jul;54(7):950-4. DOI: 10.1136/gut.2004.061283. [4] Crohn’s and Colitis UK (2020), Adalimumab. Available at: https://crohnsandcolitis.org.uk/info-support/information-about-crohns-and-colitis/all-information-about-crohns-and-colitis/treatments/adalimumab
