The immune system’s tumor-fighting T cells work best 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 killing ability of tumor-specific T cells. But neither approach has worked well in patients with established tumors.
Combining these two approaches, a new study published online on August 25th in the Journal of Experimental Medicine, caused small tumors to shrink but had no effect on large tumors. This finding suggested that some quality of large tumors makes them resistant to T cell killing.