Researchers apply a novel reverse genetics approach to create recombinant SARS-CoV-2
San Antonio, Texas (October 1, 2020) – Researchers at Texas Biomedical Research Institute (Texas Biomed) recently published findings from an innovative SARS-CoV-2 study that will assist in the development of new vaccines and antivirals for COVID-19. Through the process of reverse genetics via bacterial artificial chromosome (BAC), scientists have created a recombinant SARS-CoV-2, which is a cloned virus that behaves like the original virus both in cultured cells and hamsters. This is the first SARS-CoV-2 study using this approach, which will facilitate the development of live-attenuated vaccines to combat the disease. The study was led by faculty member Luis Martinez-Sobrido, Ph.D. Lead author of the paper published in the journal mBio was Chengjin Ye, Ph.D., who is a postdoctoral fellow in Dr. Martinez-Sobrido’s laboratory at Texas Biomed.
SARS-CoV-2 is the causative agent of the disease COVID-19. It emerged in December 2019 in Wuhan, China and has affected millions of people and impacted public health systems worldwide. Several vaccine candidates are in clinical trials. To date, the U.S. Food and Drug Administration has not approved a vaccine or treatment for COVID-19. Scientists continue to gain knowledge of the virus while working to develop new vaccine platforms and antivirals to treat the disease.
The team aimed to provide the framework to alter the SARS-CoV-2 virus genome and create a recombinant virus (rSARS-CoV-2), which will open doors to further understand the mechanisms behind infection. To accomplish this, scientists generated a BAC plasmid in the lab, which contains the entire virus genome. The scientific team is highly accomplished in this technique for other viruses and conducts the research under rigorous research standard practices.
“The BAC plasmid serves as a carrier to generate recombinant SARS-CoV-2 (r SARS-CoV-2). Once this single BAC plasmid is introduced into a cell, it leads to the generation of a recombinant virus,” explained Dr. Ye. “We used this same process in a Zika study; however, it was more challenging with SARS-CoV-2 because the virus contains around 30,000 nucleotides in its genome, which appears to be the largest RNA virus.”
Working with this BAC, scientists can alter the genome sequences and measure the characteristics it produces. It’s essentially a building block in the development of disease prevention measures, such as vaccines. Scientists continue to work on the development of attenuated viruses to create a live attenuated vaccine.
To ensure the recombinant virus resembles its original, scientists evaluated its behavior within a cell, sequenced the virus to verify its genetic identity and tested disease progression in golden Syrian hamsters. These animal models were infected with either rSARS-CoV-2 or the original virus through the nasal cavity to compare disease progression.
“These hamsters have been shown to be a good rodent model to investigate replication, virulence or strength of the virus and disease progression. We observed the virus had the same characteristics as the original virus isolate and, therefore, did not naturally mutate,” Dr. Ye said. “This is important because now you have a virus much the same as SARS-CoV-2 that can be altered to reduce its potential to cause disease.”
Dr. Martinez-Sobrido and his team are testing rSARS-CoV-2 using transgenic mice to compare results from the hamsters as well as identify a better model.
Using these BAC-based SARS-CoV-2 reverse genetics approaches, Dr. Ye has created reporter viruses expressing fluorescent and luciferase proteins to see exactly where the virus is going and what it does in the host. Currently, Dr. Ye is removing several proteins in the viral genome to identify which one(s) can result in attenuated forms of the virus to create live attenuated vaccines for the treatment of SARS-CoV-2 infections.
The study has already proved to be beneficial to other institutions researching SARS-CoV-2, as Texas Biomed has provided this rSARS-CoV-2 virus to other researchers for both basic and preclinical studies.
Dr. Cory Hallam, VP of Business Development for Texas Biomed, credits the study to the advanced capabilities and expertise of Texas Biomed scientists, saying, “Groundbreaking studies like this is what Texas Biomed is known for. Both the technology and expertise of Dr. Martinez-Sobrido and his lab allowed us to generate an effective recombinant virus. Currently, we’re working with other labs to deliver the plasmid in order for them to move their research forward, as well as conduct fluorescent reporter virus studies to identify antivirals and neutralizing antibodies for the treatment of SARS-CoV-2 infection.”
Other team members on this project include: Professor Tim Anderson, Ph.D., Staff Scientist Roy Nelson Platt II, Ph.D., fourth-year Ph. D. student Kevin Chiem, Texas Biomed post-doctoral fellows Jun-Gyu Park, Ph.D., Fatai Oladunni, Ph.D. and collaborators Fernando Almazan, Ph.D., Department of Molecular and Cell Biology, The National Centre for Biotechnology, Madrid, Spain and Professor Juan Carlos de la Torre, Ph.D., Department of Immunology and Microbiology, Scripps Research Institute, La Jolla, California.
This research was partially funded by the support of Texas Biomed donors, whose COVID-19 philanthropic donations made the realization of this study possible.
Texas Biomed is one of the world’s leading independent biomedical research institutions dedicated to eradicating infection and advancing health worldwide through innovative biomedical research. Texas Biomed partners with researchers and institutions around the world to develop vaccines and therapeutics against viral pathogens causing AIDS, hepatitis, hemorrhagic fever, tuberculosis and parasitic diseases responsible for malaria and schistosomiasis disease. The Institute has programs in host-pathogen interaction, disease intervention and prevention and population health to understand the links between infectious diseases and other diseases such as aging, cardiovascular disease, diabetes and obesity. For more information on Texas Biomed, go to www.TxBiomed.org.