How does ipilimumab block CTLA-4 signalling to promote an immune response against tumour cells?

Ipilimumab blocks CTLA-4-mediated inhibitory T-cell signals, increasing reactive T-effector cells that directly attack tumour cells; CTLA-4 blockade can also reduce T-regulatory function, and ipilimumab may selectively deplete these cells within tumours, increasing the intratumoural T-effector/T-regulatory cell ratio and promoting tumour cell death.