DES MOINES, Iowa >> A former Iowa State University scientist pleaded not guilty Tuesday to charges alleging that he falsified research for an AIDS vaccine to secure millions of dollars in federal funding.

Dong-Pyou Han, 57, entered his not guilty pleas to four counts of making false statements during his initial court appearance in Des Moines federal court. Each count carries a maximum sentence of five years in prison and a $250,000 fine.

Han was released on bond and his trial was scheduled for Sept. 2. Han and his attorney, Joe Herrold, declined to comment after the hearing.

Han, who was born in South Korea, was guided through the proceedings by an interpreter in California who attended the hearing by phone. The only time he addressed the court was to say “yes” when asked if he understood the charges.

The hearing was initially scheduled for last week, but Han was hospitalized after getting into a traffic accident in Ohio, where he has been living since resigning from Iowa State last fall. Magistrate Judge Celeste Bremer said Han has indicated he plans to move back to Iowa, where he will be under the jurisdiction of federal probation officers, and she thanked him for managing to make it to the rescheduled hearing.

“I’m sorry to hear about your car accident and I’m glad you’re out of the hospital,” she said.

According to prosecutors, Han wrote a letter to university officials before he resigned last fall in which he confessed that he had spiked samples of rabbit blood with human antibodies to make an experimental HIV vaccine appear to have great promise. Han told them he started the fraud in 2009 “because he wanted (results) to look better” and that he acted alone.

“I was foolish, coward, and not frank,” he allegedly wrote.

Han’s actions raised hopes of a breakthrough in the scientific community. But the alleged misconduct was uncovered last year after scientists at Harvard University discovered the spiked samples.

According to the indictment, Han’s misconduct caused colleagues to make false statements in a federal grant application and progress reports to the National Institutes of Health.

The NIH paid out $5 million under that grant as of last month. Iowa State has agreed to pay back NIH nearly $500,000 for the cost of Han’s salary.

Experts say it is extremely rare for criminal charges to be brought in cases of scientific fraud, but that Han’s alleged wrongdoing was extraordinary.

There have been only a handful of instances over the past 30 years in which criminal charges were brought in cases of alleged scientific fraud, Ivan Oransky, who co-founded of Retraction Watch, which tracks research misconduct, recently told The Associated Press.

Oransky said charges are rarely brought because the U.S. Office of Research Integrity, which investigates misconduct, doesn’t have prosecution authority, and most cases involve smaller amounts of money. However, he said Han’s case was “particularly brazen.”