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Envigo is addressing the need for models that mimic the long-term effects of COVID-19

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Envigo, an Inotiv company, is leading the charge to advance therapeutic research for long COVID with an enhanced humanized ACE2 mouse model

In a collaboration with Dr. Mukesh Kumar, Assistant Professor of Infectious Diseases at Georgia State University, Dr. Justin Zhao​, Director of Scientific Development for Genetically Engineered Models and Services at Envigo, has worked to develop a commercially available humanized ACE2 (hACE2) mouse model that closely resembles the physiological and biochemical features of human infections with SARS-CoV-2. This unique model was designed to support the research of COVID-19 diagnostics and therapeutics as well as monitor the long-term effects of a SARS-CoV-2 infection in human organs.

“Envigo recognized the need to develop a model that was more representative of the entire spectrum of SARS-CoV-2 infection in humans,” explained Dr. Kumar. “Most human coronaviruses are unable to cause any significant disease in wild type laboratory mice. It’s also been observed that SARS-CoV-2 infection in other hACE2 mouse models—including K18-hACE2 mice—typically results in very rapid lethal respiratory and neurological disease, suggesting limited relevance of these models for diagnostic and therapeutic testing in long COVID.”

Creating a specialized model

To help scientists better understand long COVID and other post-COVID conditions, it was important to develop a mouse model that could recapitulate moderate SARS-CoV-2 disease in humans.  

After examining the current limitations of various models, a team of scientists at Envigo worked to create a mouse model where the endogenous rodent ACE2 receptor was replaced with the human ACE2 protein.

“Most of commercially available human ACE2 expressing mice are transgenic models with multiple copies of a transgene construct and a random integration site. Therefore, the human ACE2 expression levels and tissue specificity in those mice differ from the endogenous expression of the mouse Ace2​ gene,” stated Dr. Zhao.

To overcome the limitations seen in these other commercially available models, Envigo integrated a codon optimized human ACE2​ cDNA into the mouse Ace2​ gene locus. This ensures that expression of the human ACE2 protein is driven by the mouse Ace2​ gene promoter and other regulator elements, while expression of the mouse Ace2​ gene is disabled.

“The method we used to create our humanized ACE2 mouse model,” said Dr. Zhao, “allows the human ACE2 receptor to be expressed at physiological levels and in appropriate tissues with no expression of the mouse protein. This means that researchers don’t have to contend with any effects of having human and mouse ACE2 receptors expressed in the same model.”

After Envigo validated their new model to show that it expresses only the human gene and protein—and not those of the mouse—they then needed to test the model to verify that it can show moderate infection symptoms like humans.

Testing the infectivity of the hACE2 mouse model

Envigo chose to partner with Dr. Kumar at Georgia State University to test the model’s infectivity. As a trained veterinarian, virologist and immunologist, Dr. Kumar is experienced in using various molecular, cellular and genetic approaches to investigate host-pathogen interaction and immune response to pathogens in mammalian systems. His lab has been involved in studying the pathogenic mechanisms underlying the development of lung and brain dysfunction during SARS-CoV-2 infection, making the partnership with Envigo ideal.

“One of the research areas my lab is studying is the long-term neurological consequences of SARS-CoV-2,” said Dr. Kumar. “When investigating the infectivity of the hACE2 mouse from Envigo, we saw that it could survive a severe infection, meaning that it was more likely to show long-term symptoms. This unlocks our ability to study long COVID and potentially find treatments and therapies.”

Creating additional genetically engineered models to support COVID-19 research

Beyond the hACE2 mouse model, specialized scientists at Envigo are working to provide researchers with additional tools to better understand SARS-CoV-2.

“We have generated a hACE2 rat model, as rats are an excellent model for neurological and cardiovascular studies,” said Andrew Brown, Director of Commercial Development. “We’ve also created a humanized TMPRSS2 mouse and are most excited about our double knockin mouse model that expresses both human ACE2 and human TMPRSS2 to closer mimic SARS-CoV-2 infections in humans.”

“The scientists in our transgenic model development team have a long history of generating mouse and rat models that enable advances in the study of human diseases,” said Mike Garrett, Chief Commercial Officer at Envigo. “By serving our research community through expert use of cutting-edge gene editing technologies, we aim to provide the tools they need, enable consistent research, and help advance the study of therapeutics targeting COVID-19 disease.”