Researchers have identified an immune system protein that helps to shield growing tumors from attack by circulating T-cells.
Professor John Lambris and colleagues at the University of Pennsylvania School of Medicine discovered that the protein C5a, which is part of the complement system, recruits myeloid-derived suppressor cells, which block tumor-fighting CD8+ T-cells, to form a molecular shield around growing tumors.
Until this discovery was made it was believed that the complement system helped the body to fight cancer, and some cancer treatments are actually designed to boost the immune system’s ability to destroy tumors. However, this new research shows that certain conditions can actually cause the complement system to turn against its host and promote tumor growth.
The researchers also found that blocking the C5a receptor impaired tumor growth at a rate similar to that of the chemotherapy drug Paclitaxel. It is hoped that this discovery could lead to the development of new cancer treatments that have significantly less side effects than those caused by current chemotherapy drugs.
The authors conclude: “Our study demonstrates a therapeutic function for complement inhibition in the treatment of cancer.”
Markiewski MM, DeAngelis RA, Benencia F, Ricklin-Lichtsteiner SK, Koutoulaki A, Gerard C, Coukos G, Lambris JD. Modulation of the antitumor immune response by complement. Nature Immunology. Published online: 28 September 2008 | doi:10.1038/ni.1655
