India's CSIR-Centre for Cellular and Molecular Biology (CCMB) on Thursday announced that it has established a stable culture of coronavirus, which will enable the premier research centre to work towards vaccine development and testing potential drugs to fight COVID-19. Over the last month and a half, the CCMB established stable cultures of COVID-19 causing coronavirus, SARS-CoV-2, from patients' samples.

A team of researchers led by CCMB virologist, Dr. Krishnan H. Harshan have isolated infectious viruses from several isolates. The ability to culture the virus in the lab enables the CCMB to work towards vaccine development and testing potential drugs to fight COVID-19. It also makes them a potential donor of the culture to other authorised centres that can continue growing the virus for their own use.

Explaining how SARS-CoV-2 affects humans, he said that it infects epithelial cells in human respiratory tract. "The viruses infect these cells by interacting with receptor proteins called the ACE-2 following which the virus is internalised by a process namely endocytosis. Virus RNA is later released into the cytoplasm of the cells where it makes viral proteins first and then starts to replicate the genomic RNA. Thus, the virus uses resources from these cells to make more copies of itself. Therefore the virus needs a set of host factors that allow it to replicate."

"Primary epithelial cells generated from human origins do not grow for many generations in labs, which is key to culturing viruses continuously. And hence, CCMB and other labs who are growing the virus need an 'immortal' cell line," says Dr Harshan.

They use Vero cells - kidney epithelial cell lines from green African monkey, which express ACE-2 proteins and carry a mutation that allows them to proliferate indefinitely.

"Using the Vero cell lines to grow the coronavirus, the CCMB is now in a position to isolate and maintain viral strains from different regions. We are working towards producing viruses in huge quantities that can be inactivated, and used in vaccine development and antibody production for therapeutic purposes," said CCMB Director, Dr Rakesh Mishra.

He said the CCMB also started testing potential drugs with other partners such as Defence Research and Development Organisation (DRDO) using this viral culture. "We hope that such systems are replicated at multiple research institutes and private companies to become a useful resource in the fight against this pandemic as well as for future preparedness," he said.

Researchers pointed out that historically, attenuated or killed viruses are used as vaccines in several cases, such as in the case of polio. Though the inactivated virus can not initiate infection, their structural proteins trigger antibody production in the cells. The efficacy of inactivated SARS-CoV-2 as vaccine candidate is currently being investigated by several groups.

Inactivated viruses can also trigger antibody response in other mammalian hosts in addition to humans. Various such hosts are currently under test for their efficiency of antibody response. They can vary from small rodents such as mice to large mammals such as horses and camels. Such antibodies generated in these non-human hosts can be purified and processed for injecting into humans.

The researchers believe virus culture will also help in testing of various disinfectants. Currently there is a huge need for surface disinfectants that can kill SARS-CoV-2 on various surfaces including PPE kits and clothes. Virus culture is a key component in studies that can test the efficacy of several proposed disinfectants. The ability of the key ingredients of the disinfectant will be tested for their ability to kill the virus.

SARS-CoV-2 culture will also be helpful in testing of instruments. Ultraviolet rays (UV) are well-known agents that can effectively kill virus particles and prevent infection. There is a huge demand both for domestic and industrial activities to eliminate SARS-CoV-2 from various materials including packaging materials. Such instruments need to be tested for their efficiency in killing SARS-CoV-2 after exposing virus cultures to the UV rays.