Abstract: The present invention is directed to methods of modulating the function of granular immune effector cells. It has been discovered that the secretory lysosomes of immune effector cells function as signalling hubs which direct effector functionality of the cells. By increasing or decreasing the signalling potential of the secretory lysosomes of the immune effector cells, effector functionality may be enhanced or reduced, and thus activity of the immune effector cell increased or decreased, respectively. The present invention provides methods for preparing immune effector cells for adoptive cell transfer, in which the cells are contacted with an agent which increases the signalling potential of secretory lysosomes, thus providing enhanced immune effector cells.