On a farm outside Sioux Falls, South Dakota, a herd of cloned, genetically engineered cattle are busy incubating antibodies against the Ebola virus.

Researchers hope the cattle - which certainly don't look like anything special - will produce gallons of blood plasma that could be used to treat people with the deadly virus, which has infected more than 21,000 people in West Africa and killed 8,500 of them.

"These animals produce very high levels of human antibody," said Eddie Sullivan, president and CEO of SAb Biotherapeutics, the company that developed the cattle.

The cattle have been genetically engineered with human DNA so that their bodies don't produce cattle antibodies but human antibodies. They're cloned to make a herd of genetically identical, part-human animals.

Then they are vaccinated against various deadly diseases such as Ebola. Their bodies produce antibodies in response to these vaccines, and the hope is these antibodies can be used to treat people with the diseases.

The approach is similar to the idea behind transfusing plasma from Ebola survivors into patients. No one knows if it is actually helping, but experiments are under way in Liberia and at Emory University Hospital in Atlanta to see if the blood of survivors might kick-start the immune response in a patient.

When a person or animal is infected, the body produces antibodies and immune cells to fight the invading germs. The human immune system is especially advanced and can produce both antibodies and immune cells called T-cells that "remember" a previous infection and can often prevent a second infection by the same germ.

Many Ebola patients have been transfused with either whole blood or serum, which has the red blood cells removed. No one knows if it has helped but doctors hope it does.

Ebola survivor Dr. Kent Brantly has to date given more than a gallon of his own blood plasma for such treatments.

Using cattle might make the project larger-scale. "From these animals, we can collect 30 to 60 liters of plasma each month," Sullivan told NBC News. "That translates into something between 500 to 1,000 human doses per month per animal."

The company, working in partnership with the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), has been testing the approach against hantavirus, a rare killer virus that causes regular outbreaks, including one that killed three campers at Yosemite National Park in 2012.

Experiments using an Ebola vaccine were fast-tracked when the epidemic broke out in Liberia, Sierra Leone and Guinea last year.

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