They says the cells eventually become "exhausted" in their battle against persistent viral infection and less effective in fighting the disease.
In a study to be published Dec. 28 on the journal Nature's Web site, researchers at Dana-Farber Cancer Institute and Emory University have traced the problem to a gene that turns off the infection-fighting drive of CD8 T cells in mice.
Researchers 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.
In mouse studies, CD8 T cells were reinvigorated by PD-1/PD-L1 blockers.
If human CD8 T cells are found to operate by a similar mechanism, the new findings may offer a simple immunological strategy for treating chronic viral infections, researchers said.
Freeman's lab is also exploring whether anti-cancer T cells become exhausted in various types of tumors and in HIV-infected individuals.
Freeman and his collaborators have recently received a grant from the Bill and Melinda Gates Foundation's Grand Challenges in Global Health program to extend their findings to hepatitis C infection.
Notable deaths of 2014 [PHOTOS]