Thumbi Ndung'u left Kenya 1995 to study medicine at Harvard. He later returned to Africa on a mission to exploit HIV's vulnerabilities. Now the head of the HIV Pathogenesis Program at the University of KwaZulu-Natal in South Africa, Ndung'u spoke with Scientific American contributor Brendan Borrell about a research breakthrough early in his career that helped set the pace for the Kenyan's ongoing study of genes in the immune system that may help to fight AIDS and lead to a vaccine. When asked which moment has been the most exciting of his young career, Ndung'u responded:

"The most exciting moment for me was when I succeeded in developing the first molecular clone of HIV subtype C as a graduate student at Harvard in the late 1990s. HIV subtype C is the most common subtype in the world. About 50 percent of all infections are caused by subtype C, but developing an infectious clone was difficult for reasons that we don't fully understand.

"An infectious clone is when you take a virus and put it in a bacterial plasmid [a circular strand of DNA] so that you can grow it over and over again. The example that I like to use is that it's almost like a cassette recording of the entire genetic information of the virus. Every time you need to use the virus in a well-controlled experiment in the laboratory, you can then get that infectious molecular clone and put it in a cell to make copies of it.

"I'd been trying for three years to make a clone, and was getting very frustrated. There were many other groups around the world that had also been trying and had not been successful. Once we had what we thought was a clone, we ran a series of experiments to make sure we had the full length of the HIV inserted. Then we put it into cells and waited for several days before testing whether we were getting active virus production. We were.

"It's hard to say what we did that was different from other groups, but I probably just kept trying until something worked. It also took a bit of luck."

Image courtesy of Jodi Bieber