The immune system's tumour-fighting T cells are the most effective when maximally activated. Scientists have achieved this by blocking molecules that dampen the cells' activation, or by removing a population of regulatory T cells that block the killing ability of tumour-specific T cells.
But neither approach has worked well in patients with established tumours.
In a study conducted using mouse model, the researchers found that combining these two approaches caused small tumors to shrink but had no effect on large tumors, as blood vessels around large tumours lacked proteins required for killer T cells to crawl out of the circulation and into the tumour.
Radiation therapy has been shown to increase the expression of these vessel proteins.
The new study showed that combining the T cell-boosting treatment with radiation therapy was effective in shrinking large tumours.
The researchers would be conducting further studies to see whether combining radiation therapy with T cell-boosting drugs will be effective in humans.
The new study will be published online in the Journal of Experimental Medicine.