Scientists are working to genetically engineer the immune cells of HIV patients so they become HIV-resistant, according to interim results presented Wednesday at the 18th Conference on Retroviruses and Opportunistic Infections in Boston.

Dr. Carl June, a gene-therapy expert at the University of Pennsylvania, and colleagues collected CD4 T cells from HIV patients' own blood for the procedure. The team used "zinc fingers" to snip out a single gene in the collected T cells so that they lacked CCR5, a receptor HIV needs to enter the cell. The engineered cells were then injected back into their donor.

The first of nine patients in the study received a single infusion in July 2009. In all nine, the engineered cells remain HIV-free and have multiplied to an average 6 percent of the patients' T cells. No serious adverse events were reported, though all experienced temporary symptoms such as headache, chills or fever.

"It's a big accomplishment because this is the first successful attempt at genetic editing," said June. "It gives us an essential tool."

"This is elegant work, scientifically very sound, and an important ‘proof of concept,'" said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. NIAID funded research that was foundational to the study. California-based Sangamo BioSciences, which developed the zinc fingers used like molecular scissors to delete or insert specific genes, is funding human testing of the T cells.

"It's a step," said co-investigator Pablo Tebas. "It's a step in a long process." Plans for a clinical trial of the therapy are underway.