A Seoul National University (SNU) medical team has bred four cloned cows that are less susceptible to bovine spongiform encephalopathy (BSE), or mad cow disease.

SNU professor Hwang Woo-sok announced the breakthrough Wednesday, saying the cloned cows possess antibodies specifically targeted against abnormal prions, which cause mad cow disease.

An abnormal prion is a diseased protein that triggers BSE and causes the destruction of brain tissue.

Hwang said researchers injected the prion-variation proteins into the calves while they were in utero in a bid to prevent infestation.

The team later detected the BSE-resistant genes in the calves following their birth and subsequently applied for an international patent on the genes.

Researchers also plan to send additional cloned calves from 15 pregnant cows to research facilities in Tsukuba, Japan to verify the research results.

Beef contaminated with mad cow disease consumed by humans can cause a variant of Creutzfeldt-Jakob disease, which has claimed 139 lives around the world so far.