Joep Lange led many early drug trials of HIV therapies and studied how to prevent HIV-positive pregnant women from transmitting the virus to their babies. Jean Ayissi/AFP/Getty Images hide caption

itoggle caption Jean Ayissi/AFP/Getty Images

AIDS drugs line a pharmacy's shelves. A new recommendation from the World Health Organization suggests a daily anti-HIV pill for men who have sex with men. Astrid Riecken/MCT/Landov hide caption

itoggle caption Astrid Riecken/MCT/Landov

Human immunodeficiency virus Type 1 inserts its genetic material into the DNA of human cells, turning them into little HIV factories. Eye of Science/Science Source hide caption

itoggle caption Eye of Science/Science Source

HIV particles (red) invade a human immune cell. When HIV is transmitted through sex, only the strongest versions of the virus establish long-term infection. Chris Bjornberg/ScienceSource hide caption

itoggle caption Chris Bjornberg/ScienceSource

HIV/AIDS drugs like AZT are lifesavers for many people. But insurers' policies on paying for the drugs vary widely. Will & Deni McIntyre/Science Source hide caption

itoggle caption Will & Deni McIntyre/Science Source

The mask of this Kiev protester (at a 2012 demonstration demanding more funding for HIV treatment) reads "quarantine." There are enough drugs to treat only half the HIV patients in Ukraine. Sergei Supinsky/AFP/Getty Images hide caption

itoggle caption Sergei Supinsky/AFP/Getty Images

While not conclusive, the two cases are "quite promising," says Anthony Fauci, a longtime AIDS researcher who directs the National Institute of Allergy and Infectious Diseases. Alex Wong/Getty Images hide caption

itoggle caption Alex Wong/Getty Images

When Benta Odeny was diagnosed with HIV, she started to protect her husband Daniel from the virus by taking antiretroviral medications. The same drugs also helped her give birth to an HIV-negative daughter, Angelia. Gregory Warner/NPR hide caption

itoggle caption Gregory Warner/NPR

A mother waits with her child at an HIV clinic in Nyagasambu, Rwanda, in February 2008. The clinic was built with a grant from the President's Emergency Plan for AIDS Relief initiative. Shashank Bengali/MCT /Landov hide caption

itoggle caption Shashank Bengali/MCT /Landov

President Obama walks into an auditorium in the Eisenhower Executive Office Building Monday for a speech about World AIDS Day. Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP