MELBOURNE researchers have discovered the immune system's "kill switch" that destroys blood stem cells when the body is fighting infection or chemotherapy.

Walter and Eliza Hall Institute of Medical Research scientists say the findings could lead to treatments for the life-threatening condition of sepsis and could help recovery from chemotherapy.

The body has a protective mechanism that instructs the immune system and blood stem cells to die when it senses infection.

But the team found this can go too far, particularly in cancer patients with infections and those with sepsis.

The findings, published in the journal Immunity, shows this abnormal response to infection can cause too many stem cells to die until the patient can't recover their immunity, putting their life in danger.

By blocking these signals, the researchers stopped the blood stem cells from self-destructing, stopped cell death after chemotherapy and boosted recovery from infection.