According to John D. Lambris, PhD, the protein C5a, which is produced during an immune response to a developing tumour, helps tumours build molecular shields against T-cell attack.
C5a belongs to the complement system, one of the body's immune defenses against pathogens. If the system proteins get activated they can relieve the body of microbes and foreign cells.
In fact, a large number of cancer treatments are aimed at boosting the immune system to kill tumours.
"Until now, everyone thought that the complement system was there to eliminate tumor cells. We found that in some conditions, the complement system can promote tumor growth, depending on the specific tumor and the specific environment in which the tumors are developing," Nature quoted Lambris as saying
But, the scientists discovered that in a mouse model, activation of the complement system in tumour tissue leads to the generation of C5a.
C5a then ropes in myeloid-derived suppressor cells (MDSC) to tumours. The MDSCs block the function of CD8+ T cells, which would normally dismantle a tumour.
The scientists also found that blocking the C5a receptor on cell surfaces impairs tumour growth at the same rate of Paclitaxel, a chemotherapy drug.
The discovery could lead to new cancer treatments with far fewer side effects than chemotherapy.
"Researchers are trying to introduce immune therapies and anti-tumor vaccines, but most of these vaccines fail. We show in this study a possible mechanism how to overcome this problem," said Lambris.
The researchers are conducting studies that utilise the approaches described in this paper to five models of cancer.
The findings appeared online in Nature Immunology.