Study: Weary immune cells can recharge

ATLANTA, Dec. 29 (UPI) -- A new study has uncovered how immune cells, weary from fighting chronic viral infection, are re-energized.

Similar to prize fighters exhausted by a 15th round, CD8 T cells eventually become "exhausted" in their battle against persistent viral infection and less effective in fighting the disease, said researchers at the Dana-Farber Cancer Institute and Emory University.

But they said they have traced the problem to a gene that turns off the infection-fighting drive of CD8 T cells in mice.

"CD8 T cells that have fought viral infections retain a 'memory' of the viruses they've encountered, so they can rapidly respond to new infections from those viruses," says the study's author, Gordon Freeman of Dana-Farber.

In the case of chronic infection, senior author Rafi Ahmed of Emory pointed out that memory cells become exhausted and lose the capacity to respond to the virus.

The researchers said they found that a gene known as PD-1 was much more active in the exhausted cells.

In a study to be published Dec. 28 on the journal Nature's Web site, they said the discovery raises the possibility that CD8 cell exhaustion can be reversed in human patients, reinvigorating the immune system's defenses against chronic viral infections ranging from hepatitis to HIV, the virus that causes AIDS.

Although it's not known why CD8 cells become exhausted after about a month after infection, scientists theorize that it may be part of the body's system for naturally ending the immune response after an infection has been quelled. If it persists too long, the immune response can damage normal, healthy tissue.

In the mouse studies, CD8 T cells were reinvigorated only as long as researchers continued to administer PD-1/PD-L1 blockers, so the chance of sparking a runaway immune response seems unlikely, they said.