Complex sentence: Regulatory T-cells inhibit other T-cells, which may act to the benefit of the tumor so increasing the amount of cytotoxic T-cells and decreasing the regulatory T-cells is another mechanism in which ipilumumab increases the anti-tumor response.
Split into simpler sentences: Regulatory T-cells inhibit other T-cells, which may benefit the tumor. Increasing the amount of cytotoxic T-cells and decreasing the regulatory T-cells is another mechanism by which ipilumumab increases the anti-tumor response.