In people infected with HIV who develop broadly neutralizing antibodies, this antibody region — called HCDR3 — has about 30 amino acids, about twice as long as what is usual for human antibodies. Although on the long side for a human, “that’s actually kind of short for a cow,” Smider says.
And so the idea to immunize cows was born. Since cows naturally make longer HCDR3s, Smider explains, perhaps they’d have this sought-after response to HIV.
Smider and colleagues took serum — blood with the cells removed, leaving antibodies behind — from four immunized cows and tested it against different types of HIV virus in a test tube. All of the cows developed broadly neutralizing antibodies. The researchers then tested one cow’s antibodies on an even larger number of virus types. After 381 days, this cow’s antibodies prevented 96 percent of the 117 HIV types from infecting cells in a lab dish. The researchers also isolated an antibody from this cow that had a long HCDR3 of 60 amino acids and stopped infection by 72 percent of the HIV types.
If researchers could induce antibodies with long HCDR3s in humans, “then that could be the basis of getting a vaccine to work,” Smider says. “You need a step before the immunization that helps expand the rare antibodies.” Since cows are so good at making broadly neutralizing antibodies, it also might be possible to turn the cow’s handiwork into drugs for HIV treatment, if bovine antibodies are effective at stopping the virus in other animals, he says.