While Brown remained clear of HIV for more than a decade after being treated, he had suffered a relapse of leukemia in the past year.
His doctors said the blood cancer had spread to his spine and brain, and he had recently been in hospice care in his home town of Palm Springs, California.
For Huetter, the German doctor caring for the "Berlin Patient" in 2007, Brown's case was a shot in the dark.
The treatment involved the destruction of Brown's immune system and the transplanting of stem cells with a gene mutation called CCR5 that resists HIV.
Only a tiny proportion of people — most of them of northern European descent — have the CCR5 mutation that makes them resistant to the AIDS-causing virus.
This and other factors made the treatment the "Berlin Patient" had expensive, complex, and highly risky.
Most experts say it could never become a way to cure all HIV patients since many of them would risk death from the procedure itself.
More than 37 million people worldwide are currently infected with HIV, and the AIDS pandemic has killed about 35 million people since it began in the 1980s.