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Mixed Early Results in Covid-19 Antibody Cocktail Trial

SARS-Cov-2 viruses

Scanning electron microscope image showing SARS-CoV-2 viruses, in yellow. (NIAID, NIH)

30 Sept. 2020. The developer of a synthetic antibody cocktail to treat non-hospitalized Covid-19 patients released first results from a clinical trial with some encouraging findings. Regeneron Pharmaceuticals Inc. in Tarrytown, New York released the partial results yesterday, which have not been independently peer reviewed.

Regeneron Pharmaceuticals develops synthetic antibodies that invoke the immune system to prevent or treat infectious diseases. The company’s VelocImmune technology produces these human antibodies with genetically engineered mice. The engineered mice become living production lines, says the company, producing antibodies that respond as a human to a specific pathogen, while not affecting the rest of the animal. The antibodies are then retrieved and combined with human genetic characteristics for testing as therapy candidates.

For Covid-19, Regeneron uses a combination of two antibodies for neutralizing the SARS-CoV-2 virus, in a single drug code-named REGN-COV2, to both prevent or treat infections. The company says two antibodies are needed, each targeting a separate region of the characteristic protein found on the surface of the coronavirus spike, which penetrates and binds to receptor proteins in cells, beginning the infection process. Regeneron says the two antibodies in REGN-COV2 work in tandem, one antibody to start neutralizing the spike protein, with the second antibody blocking mutated forms of the virus that can form and escape after the initial attack.

Regeneron released early results of a clinical trial testing REGN-COV2 with some 2,100 participants patients having Covid-19 infections, but not yet hospitalized, in an adaptive, multi-stage study. A companion trial is testing the antibody cocktail with hospitalized patients. The company reports on findings from the first 275 participants in the non-hospitalized patient trial, looking primarily for changes in viral loads, alleviation of Covid-19 infection symptoms, need for follow-up medical care, and reports of adverse reactions from the antibody cocktail. Participants are randomly assigned to receive a high or low dose of REGN-COV2, or a placebo.

The study team first tested participants for the presence of SARS-CoV-2 antibodies before being given REGN-COV2 or the placebo, with separate findings given for seropositive participants, those already with antibodies in their blood, and seronegative participants, those without antibodies. As expected, seropositive participants started with much lower viral loads than seronegative participants. Among placebo recipients, says Regeneron, seropositive participants cleared their Covid-19 symptoms in a median of seven days, while seronegative participants required a median of 13 days.

The company reports seronegative participants receiving REGN-COV2 experienced larger reductions in viral loads after seven days than placebo recipients. Recipients of the high-dose formulation experienced a large enough reduction in viral load to be statistically reliable, but viral load reductions among low-dose seronegative recipients were not large enough for statistical reliability. Likewise, the greater the viral loads among recipients at the beginning of the trial, the larger the reduction of viral loads for both high- and low-dose recipients.

Both high- and low-dose REGN-COV2 recipients among seronegative participants experienced more alleviation of their Covid-19 symptoms than placebo recipients, according to Regeneron. But seronegative participants were also more likely to need additional medical help, either through emergency room, urgent care, and telemedicine visits, or hospitalizations in 5 percent of low-dose, 8 percent of high-dose, and 15 percent of placebo recipients. The study team says REGN-COV2 was generally well-tolerated, with four participants experiencing infusion site reactions, and serious adverse effects experienced in one low-dose and two placebo recipients, but no high-dose recipients.

George Yancopoulos, president and chief scientist at Regeneron, says in a company statement, “The greatest treatment benefit was in patients who had not mounted their own effective immune response, suggesting that REGN-COV2 could provide a therapeutic substitute for the naturally-occurring immune response.” The company says it plans to quickly submit detailed results from the trial for publication, to share insights with the public health and medical communities.

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