A scientist and former professor at Iowa State University has pleaded not guilty to charges that he faked research claiming to have found an AIDS cure, the Associated Press reported.

Dong-Pyou Han, 57, is accused of falsifying research that boasted an AIDS vaccine in order to secure millions in funding from the National Institutes of Health. The South Korean native was charged with four counts of making false statements, which altogether carry a five-year prison sentence and a $250,000 fine, the AP reported.

Han resigned from his position at ISU in fall 2013 after he confessed in a letter that he tampered with experiments conducted to find an HIV vaccine, prosecutors said.

In the letter, Han allegedly admits to contaminating samples of rabbit blood with blood from humans who were HIV positive. The human blood contained antibodies produced to fight AIDS. The antibodies made it seem as if the rabbit blood produced them on its own, thus giving the appearance of an AIDS cure.

Han's success was lauded by the medical community between 2010 and 2012 as groundbreaking. But Harvard University scientists discovered last year the samples were tainted, the AP reported.

"I was foolish, coward, and not frank," wrote Han, who remains out on bail.

Han was also awarded millions of dollars in grants from the National Institutes of Health, $5 million of which was paid as of June. ISU agreed to pay back nearly $500,000 to cover Han's salary, the AP reported.

Experts say it is rare for someone to be tried for faking scientific research. That is due in part to the fact that the U.S. Office of Research Integrity, which handles such cases, does not have the right to press charges, according to Recreation Watch co-founder Ivan Oransky. The organization keeps track of falsified research.  

What Han did, however, was "particularly brazen," Oransky told the AP.

Han's trial is set for Sept. 2.