The biotechnology firm Regeneron said it has now developed hundreds of potential medicines that could work against the novel coronavirus that causes Covid-19, and that it may enter clinical trials by early summer.

Regeneron’s drugs are what are known as monoclonal antibodies, proteins produced by the immune system that can neutralize pathogens. Regeneron’s antibodies are made in mice that have been genetically modified to have human-like immune systems, which means that, when they are given to a patient, his or her immune system will not attack the antibody.

The technology was previously used to create a cocktail of antibodies that had some efficacy against the Ebola virus, Regeneron said last year.

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“The most tried-and-true near-term approach, in terms of prophylaxis, is making highly potent neutralizing antibodies against the virus itself,” said George Yancopoulos, Regeneron’s co-founder and chief scientific officer, in an interview. “The landmark is to see how rapidly we could get to this point,” he said.

To battle Covid-19, Regeneron says it wants to select two antibodies against the virus, which is known as SARS-CoV-2. The antibodies target a protein on the virus’ outer shell, called the spike protein. Having two antibodies targeting the spike protein in the treatment, not one, should mean that it is more difficult for the virus to mutate in a way that will allow it to evade both antibodies.

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Regeneron said in a press release that its scientists have isolated hundreds of virus-neutralizing antibodies from its mice, and more from patients who have recovered from Covid-19. It will choose two of these based on their potency and other “desirable qualities” like specificity, ability to be manufactured easily, and durability in the body.

By mid-April, Regeneron said, it will be ready to start preparing to do large-scale manufacturing. If all goes perfectly, human clinical trials could begin by early summer. Those studies would then have to show that the antibodies are effective. Regeneron plans to test its antibody study both to treat people who have Covid-19, and as a prophylactic that would prevent people from being infected with the SARS-CoV-2 virus. It’s possible, if everything goes right, that an antibody could be available for some uses by the fall. “Things have never been done this fast before,” Yancopoulos said. A lot of things have to go right, he said.

It is likely that developing a drug as a treatment will take less time than proving it can prevent infection; the latter requires much bigger and longer studies. Regeneron also said that it is working with the Department of Health and Human Services’ Biomedical Advanced Research and Defense Authority, or BARDA, to further increase manufacturing capacity should its treatment work.

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Creating antibody drugs against the virus is seen as one of the more promising approaches to attack SARS-CoV-2. Other groups, including the teams of Biogen and Vir and Eli Lilly and AbCellera, have also announced plans to develop antibody drugs against the virus.

Regeneron is also testing an approved drug, called Kevzara, against Covid-19. The drug, which is sold in partnership with Sanofi, targets inflammation, not the virus itself. A similar drug from Roche, Actemra, showed early promise in a study in China. Answers from that study might be available in weeks to months, if patients respond quickly.

“It’s really the investment we’ve been making in these technologies for the past 30 years that allows us to be in this position right now,” Yancopoulos said. “We feel privileged at Regeneron in the investments that we’ve made, and we’re proud that we’re not alone, and that there’s an entire industry that is stepping up.”