CTLA4 and neoplasm: Examples of immune interference that lead to tumour development and progression are the secretion of IL-10 and the expression of PD-L1 and CTLA-4 by regulatory T cells (Tregs) to suppress CTL functions31 and the expression of inhibitory receptors on T cells, such as PD-1 and CTLA-4, to inactivate effector T cells32.