Scientists at the University of Rochester and UCLA have used a bit of duplicity to render human white blood cells resistant to HIV, using genetic engineering to fool the virus and disrupt its life cycle. The novel strategy is described in the June 6 issue of the Journal of Biological Chemistry.
"This turns the normal process by which HIV replicates against itself," says Joseph Rosenblatt, the lead investigator and head of Hematology/Oncology at the University of Rochester Cancer Center. "We trick the virus into shutting down its replication process prematurely."
While it's too soon to say whether the work will be clinically relevant, the scientists note that the strategy opens up a new research avenue in the gene therapy of AIDS. They have filed for a patent on the process.
To replicate itself, HIV depends on a molecule known as a tRNA primer to attach to a strand of HIV's genetic template, providing a foothold so that the enzyme reverse transcriptase can copy the viral genetic code. Initiating the copying process at precisely the right spot is the primer's critical task.
Rosenblatt's team genetically engineered a new primer, a mutant tRNA that docks at a different site on the HIV template, causing reverse transcriptase to begin copying at the wrong spot. Just like a typist whose fingers are off by one key, the result is useless -- HIV doesn't replicate, and the virus can't go on to infect more cells.
"Forcing reverse transcription to start in a different spot is a new idea," says Vicente Planelles, assistant professor at the Cancer Center, who participated in the research. "No one has previously attempted to genetically interfere with the priming process in retroviruses."
In the test tube, cells equipped with the engineered primer were infected by HIV at just one one-thousandth the normal rate of infection. The team made its measurements in cell lines of human CD4-expressing white cells, the type of helper T-cell that HIV normally attacks.
Substituting the primer with an inept impostor could be used in combination with other therapies, Rosenblatt says. Currently, protease inhibitors prevent the maturation of virus that has already infected cells, and reverse transcriptase inhibitors like AZT and Nevirapine prevent the virus from replicating within cells. The new work involves a third approach: genetically modifying a patient's cells to make them resistant to infection.
The team included scientists from the University of Rochester and UCLA. Besides Rosenblatt and Planelles, University of Rochester participants also included faculty members Robert Bambara, Pia Challita-Eid, and post-doctoral fellow Chockalingam Palaniappan. UCLA contributors included Yuanan Lu, Xinqiang Li, and Rafael Amado.
Funding for the research came from the National Institutes of Health and the Ahmanson Foundation.