There has been a lot of talk about antibodies in this pandemic.
Using antibodies to fight a virus is not new science. It’s how we naturally fight infection. The body develops antibodies that recognize the virus and attack it.
Doctors use it as therapy to fight HIV, hepatitis, Zika virus. And now, SARS-CoV-2.
But to harness antibodies for therapy, doctors need to know how much and what type of antibodies are most effective.
Doctors treat severely ill COVID-19 patients with convalescent plasma – blood, donated by those already recovered, that contains antibodies.
Dr Michael Busch is director at Vitalant Research Institute.
“It’s the quantity and specificity meaning,” he said. “It’s not just the total concentration or level of antibodies but it’s the right antibodies.”
Scientists believe SARS-CoV-2 invades the lungs when a protein on those now infamous spikes interacts with ACE-2 receptors found on the surface of healthy pulmonary cells. Once inside, the virus replicates and causes damage. That process indicates the most effective antibodies are likely ones that target those protein spikes.
“We think that the most important antibodies for preventing infection or for treating patients to reduce the virus replication in people are antibodies that bind to the spike proteins on the outside of the virus they can neutralize them from invading a cell,” Busch said. “So the antibodies that we think are the most effective are specially targeting the receptor binding domain of the spike protein. But in fact those antibodies are a minority of the antibodies that are formed in people.”
Instead, researchers are finding higher concentrations of antibodies that target proteins on the inside of the viral particle called nuclear antibodies. But in those who suffered more severe illness they had better antibodies, the neutralizing antibodies that target the spikes.
“What is being observed in our studies, and is being reported in China and U.S, is people who have more severe illness have higher levels of neutralizing antibodies than people who have mild disease,” Busch said.
The end game is a more effective and nuanced therapy harnessing the more powerful antibodies.
“Right now we are trying to help people who are dying and extremely sick by acquiring plasma from altruistic donors who have recovered,” Busch said. “And we don’t have the understanding how to select or induce antibodies in those donors to be the most therapeutically beneficial. That is going to take us many months, even years, to understand how to make the most effective plasma. So we’ll go from an early stage, which is where we are now, where we’ll essentially take plasma from any recovered person that meets some minimal level of antibody levels.”
Surprisingly, even though this virus is so new, SARS-CoV-2 antibodies are already in our blood supply. Vitalant screens 25,000 donations a day through it’s network.
“When we screen normal donors, which we do to understand the portion of infected, we do pick up blood donors who do have antibodies against SARS-CoV-2,” Busch said. “But levels are significantly lower than those we are seeing in samples from patients who are coming back after they develop severe illness.”
Busch says right now patients receive convalescent plasma from a single donor, but down the road, he believes a pool plasma will be administered, meaning a collection of blended plasma from multiple donors combined to be a more potent and effective therapy.