Why is HIV so hard to cure?

Why is HIV so hard to cure?

HIV infects a kind of white blood cell called a CD4 lymphocyte, a key player in the immune response. What makes HIV so sneaky is that it infects the very cells that are supposed to rub out viral infections.

HIV replicates in CD4 cells when they are activated -- that is, when they are triggered by an infection. But some HIV-infected cells become inactive before the virus replicates. They go into a resting mode -- and the HIV inside them becomes dormant until the cell is activated.

HIV drugs don't affect HIV hiding in resting cells. These cells represent a hidden reservoir of HIV. When treatment stops, the resting cells eventually become active. The HIV inside them replicates and quickly spreads. That's why current HIV treatments don't cure HIV.

How was the Berlin patient cured of HIV?

The Berlin patient was 40 years old when he developed leukemia. He had been infected with HIV for more than 10 years, but he was keeping his infection under control with a standard HIV drug regimen.

Standard treatment for leukemia is to kill off most of a patient's blood cells with chemotherapy -- a process called conditioning -- and then to rescue the patient with infusions of stem cells from a matched donor's blood or bone marrow. The new stem cells then repopulate the immune system and kill off the leukemia cells that survived the conditioning treatment.

The patient's doctor, Gero Hütter, MD, had an idea. Since HIV hides in white blood cells, why not try to cure the patient of leukemia and HIV at the same time? Instead of a normal donor, Huetter looked for a donor who carried the relatively rare mutation called CCR5delta32.

People with this mutation lack functional CCR5, the keyhole that HIV most often uses to enter cells. People who inherit two copies of this gene are highly resistant to HIV infection. So Hütter found a stem-cell donor who carried this mutation and used the cells to repopulate his patient's immune system.