Activated granulocytes and granulocyte-derived hydrogen peroxide are the underlying mechanism of suppression of T-cell function in advanced cancer patients

Impaired T-cell function in patients with advanced cancer has been a widely acknowledged finding, but mechanisms reported thus far are those primarily operating in the tumor microenvironment, Very few mechanisms have been put forth to explain several well-described defects in peripheral blood T cell s, such as reduction in expression of signaling molecules, decreased produc tion of cytokines, or increased apoptosis, We have closely examined the per ipheral blood mononuclear cell (PBMC) samples derived from patients and hea lthy individuals, and we have observed an important difference that may und erlie the majority of reported defects. We observed that in samples from pa tients only, an unusually large number of granulocytes copurify with low de nsity PBMCs on a density gradient rather than sediment, as expected, to the bottom of the gradient. We also show that activating granulocytes from a h ealthy donor with N-formyl-L-methionyl-L-leucyl-L-phenylalaline could also cause them to sediment aberrantly and copurify with PBMCs, suggesting that density change is a marker of their activation. To confirm this, we looked for other evidence of in vivo granulocyte activation and found it in drasti cally elevated plasma levels of 8-isoprostane, a product of lipid peroxidat ion and a marker of oxidative stress. Reduced T-cell receptor zeta chain ex pression and decreased cytokine production by patients' T cells correlated with the presence of activated granulocytes in their PBMCs, We showed that freshly obtained granulocytes from healthy donors, if activated, ran also i nhibit cytokine production by T cells. This action is abrogated by the addi tion of the hydrogen peroxide (H2O2) scavenger, catalase, implicating H2O2 as the effector molecule. Indeed, when added alone, H2O2 could suppress cyt okine production of normal T cells. These findings indicate that granulocyt es are activated in advanced cancer patients and that granulocyte-derived H 2O2 is the major cause of severe systemic T-cell suppression.