Dong-Pyou Han, a former Iowa State University scientist, pleaded not guilty Tuesday regarding charges that he falsified research for an HIV vaccine to secure large amounts of federal funding.

Han, who appeared in Des Moines federal court, is facing four counts of making false statements related to the research. Each of the four counts carries a maximum five year prison sentence and a $250,000 (£145,000) fine.

Prosecutors state Han told university officials in a letter last fall that he spiked samples of rabbit blood with human antibodies to make an experimental HIV vaccine appear to have promise. Han reportedly started spiking blood in 2009, stating in the letter that he acted alone.

Han’s alleged actions were uncovered last year by Harvard University scientists who found irregularities in the research that was once considered groundbreaking.

Han’s alleged misconduct caused colleagues to unknowingly make false statements in federal grant applications and progress reports to the National Institutes of Health.

As of last month, the National Institutes of Health paid $5 million (£2,913,000) under that grant toward the research.

Iowa State University has agreed to pay back the cost of Han’s salary, which is around $500,000 (£291,300), to the National Institutes of Health.

Han was released on bond with a trial date of 2 September 2014.