Washington, Dec 14 - Chronic infections stay on because they wear the immune system out, which immunologists describe as exhaustion. Yet exhausted immune cells can be revived by introduction of fresh cells that act like coaches giving a pep talk, researchers at Emory Vaccine Centre (EVC) in the US have found.

Their findings provide support for an emerging strategy for treating chronic infections: infusing immune cells back into patients after a period of conditioning, the journal Proceedings of the National Academy of Sciences Early Edition reports.

Study co-author Rafi Ahmed, director of the EVC lab, has extensive experience studying mice infected with lymphocytic choriomeningitis virus (LCMV). Immune responses against LCMV are driven by CD8 or "killer" T cells, which destroy virus-infected cells in the body.

But a few weeks after exposure to LCMV, the mice develop a chronic infection that their immune systems cannot shake off, similar to when humans are infected by viruses like HIV and Hepatitis C, according to an Emory statement.

Rachel Aubert, Emory immunologist, and her co-workers examined what happened to mice chronically infected with LCMV when they infused CD4 or "helper" T cells from uninfected mice.

After the infusion, the CD8 cells in the infected mice revived and the levels of virus in their bodies decreased by a factor of four after a month.

Like coaches encouraging a tired athlete, the helper cells drove the killer cells that were already in the infected mice to emerge from exhaustion and re-engage.

The cell-based treatment was especially effective when combined with an antibody that blocks the molecule PD-1, which appears on exhausted T cells and inhibits their functioning.

The antibody against PD-1 helps the exhausted T cells to revive, and enhances the function of the helper cells as well: the combination reduced viral levels by roughly
10-fold, and made the virus undetectable in some mice.

"We have not seen this sharp of a reduction in viral levels in this system before," says co-author Alice Kamphorst, a postdoctoral fellow. (IANS)