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Photo by: Matt Rourke

In a Feb. 25, 2011 photo, Dr. Pablo Tebas, left, and Jay Johnson pose for a photograph at the University of Pennsylvania in Philadelphia. Tebas is leading a study testing gene therapy as a possible new way to treat and perhaps someday to cure infection with the AIDS virus. Johnson, who works for an AIDS advocacy and service organization in Philadelphia, took part in one of the studies. (AP Photo/Matt Rourke) (AP Photo/Matt Rourke)

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