Iowa State University (ISU) researcher Dr. Dong Pyou Han has resigned after admitting to research fraud in his work to find a vaccine for HIV, the virus that causes AIDS.

Han admitted to doctoring rabbit's blood to make his vaccine appear to work better against the virus. An ISU spokesman told the De Moines Register Han admitted reasonability and resigned in October.

His fake results helped ISU gain millions of dollars in federal grants, said Dr. James Bradac, who works for the National Institutes of Health as an overseer for AIDS vaccine grants.

He told the Register Monday that Han apparently added human blood components to the rabbit's to alter the results. Han used the blood of people who had produced antibodies to HIV and, when added to the rabbit's blood, made it appear that the vaccine was building a natural defense to the virus.

"This positive result was striking, and it caught everybody's attention," Bradac said.

According to a federal inquiry released Monday, Han's results were presented at scientific meetings over a period of several years. Other institutions reportedly began trying to replicate ISU's results, but were unsuccessful, leading to skepticism.

John McCarroll, an ISU spokesman, said research team leader Dr. Michael Cho was alerted in January about the suspicion. To that point, the team's fraudulent research was billed as having "exciting results."

"At Iowa State's request, the research samples in question were examined by researchers at another university; they confirmed samples had been spiked," McCarroll wrote in an email to the Register, adding that Han was revealed as the suspect in August. "He later admitted responsibility and resigned from Iowa State, effective Oct. 4, 2013."

Bradac said Cho and Han worked together for 15 years and the two transferred to ISU from Case Western Reserve University in Ohio. The team's total of federal grants reached about $19 million.

Bardac said Han most likely acted alone and Cho had no knowledge of the fraudulent activity. As such, McCarroll confirmed Cho will not be facing any disciplinary action.

Dr. Ivan Oransky, a physician and medical journalist, wrote about the sanctions against Han and said the researcher will be banned from participating in federally funded work. He said it is a harsh penalty, but also that he would like to see such activity punished by the federal government.

"This is fraud, and the question is whether it's a big enough case for the government to go after," Oransky said, according to the Register. "I think it's time for the government to criminally prosecute more of these cases."