Cancers cells in animal models use indoleamine 2,3-dioxygenase (IDO), an enzyme used by fetuses to help avoid rejection, to recruit Treg cells that turn down the immune response, report scientists at the Medical College of Georgia Cancer Center.
The study found that IDO, which seems to play a role in tumor survival despite the relatively few number of cells in the tumor’s draining lymph nodes, directly activates existing Tregs that become strongly suppressive within a day. This rapid conversion occurs only in lymph nodes connected to tumors.
The researchers also discovered that the Tregs then up-regulate the PD-L1/PD-L2 pathway, which has been shown to play an important role in the immune suppression caused by AIDS.
The study was published online in the August 16 issue of The Journal of Clinical Investigation.