Sagrario Ortega, Head of the Mouse Genome Editing Core Unit at CNIO (top centre), and members of her team. /Amparo Garrido. CNIO
A team led by Sagrario Ortega is working on the development of genetically modified mice that reproduce the SARS-CoV-2 infection in humans
Developing these preclinical models, with the help of the latest genetic engineering technology like CRISPR/Cas, would enable new approaches to Covid-19 prevention and treatment, as well as further study of the disease and its effects
The experimental models will be made available to the scientific community for further research into the disease
One of the most urgent needs in connection with Covid-19 is the development of effective antiviral drugs and vaccines that prevent a new outbreak of the disease in the future. Both developments require preclinical models to test the drugs and the prophylactic agents putting them to clinical uses. The Institute of Health Carlos III (ISCIII) is financing a project being carried out at the Spanish National Cancer Research Centre (CNIO) for the development of genetically modified mice that can be used as models for the disease in order to improve and advance therapeutic strategies. The project is being led by Sagrario Ortega, head of the Mouse Genome Editing Core Unit at CNIO.
“The laboratory mouse has many advantages as experimental animal model, but mice need to be humanised first to be used for the study of Covid-19,” Ortega explains. For this, her team will use genetic engineering approaches, including CRISPR/Cas, a revolutionary genome editing technology developed in the past few years that could reduce the time it takes to develop these models from 1 year to 3 or 4 months.
The Unit led by Ortega was among the first groups in Spain to work systematically on the design and development of genetically modified mice, using the gene targeting technique to introduce targeted mutations in the mouse genome. Today, this Unit is a reference in Spain and is also internationally renowned in the field of transgenesis and genome editing. The researchers at the Mouse Genome Editing Core Unit rely on newly developed tools based on the CRISPR/Cas technology to introduce highly complex modifications in the mouse genome in a fast and effective way. By using this technology, they create mouse models that accurately reproduce the genetic alterations associated with human diseases.
The Unit has been a pioneer in the development of genetically modified mice for the study of local and distal metastasis through lymphatic vessels, using in vivo imaging techniques, and for research into the function of the lymphatic system in tumour progression. It has also produced hundreds of genetically modified mice to advance research into various types of cancer and for the development of new tumour therapies.
“We would like to put our expertise at the service of the scientific community, making new tools available that might contribute to the development of effective therapeutic strategies against Covid-19,” Ortega remarks.
Same entry point for the virus in mice and humans
The protein ACE2 (Angiotensin Converting Enzyme-2) serves as the main gate for the virus entry into cells in the human body. Attached to the outer surface (cell membrane) of some cells, like type II pneumocytes in the lungs, endothelial cells or vascular smooth muscle cells, this enzyme is normally involved in the regulation of blood pressure. The ”spike” protein of the SARS-CoV-2 envelope binds to ACE2 on the cell surface, opening the virus way into the cells to parasitize them for its own multiplication.
“Mouse ACE2 is different from human ACE2, particularly in the domain recognized by the SARS-CoV-2 . As a result, mice are resistant to infection. Genetic engineering enables us to replace the mouse Ace2 gene with the human one so that the animals have the virus receptor in the same cells and tissues and with the same expression regulation as in humans,” Ortega observes. In addition, a fluorescent protein will be co-expressed with human ACE2 in order to identify the cells that can get infected and isolate them for further study.
At present, there is only one transgenic mouse, publicly available, for coronavirus research – Tg.K18-hACE2. Reported by researchers from the University of Iowa in 2007, it was used to study SARS-CoV-1 and is maintained at the Jackson Laboratory in Bar Harbor, Maine, USA. “This mouse model can only reproduce in part the pathologies associated with the SARS-CoV-1 infection. Besides, the waiting time for accessing these mice is six months. We want to develop more accurate models reproducing the pathologies associated with Covid-19, caused by SARS-CoV-2 infection”
The researchers have contacted other groups specialising in coronavirus at ISCIII and the Spanish National Research Council (CSIC), such as the lab directed by Luis Enjuanes at the Spanish National Centre for Biotechnology (CNB-CSIC), where they will infect the genetically modified mice with SARS-CoV-2 to move into the next phase of the project. Once validated, the mouse models will be made available to the scientific community for further research into Covid-19.
This has been CNIO’s second project financed by ISCIII’s extraordinary call for projects Covid-19 Fund. The first was the one led by Felipe Cortés (CNIO) and Luis Blanco (Severo Ochoa Molecular Biology Centre, CBMSO-CSIC), focusing on the study of a new technique for early detection of SARS-CoV-2. In addition, CNIO researchers are currently working on several projects studying a variety of aspects of Covid-19, such as the after-effects for the lungs of the respiratory infection or therapies that may block virus replication.