The present invention relates to engineered a cytolytic immune cell comprising: i) a releasable protein which comprises a polypeptide of interest (POI) and a first interaction domain； and ii) a retention protein which is retained within an intracellular compartment of the cell and comprises a second interaction domain which binds to the first protein interaction domain, wherein binding between the first protein interaction domain and second protein interaction domain is disrupted by the presence of an agent, such that in the absence of the agent, the first protein interaction domain and second protein interaction domain bind and result in retention of the POI within an intracellular compartment； whereas in the presence of the agent, the first protein interaction domain and second protein interaction do not bind and the POI is released from the intracellular compartment and expressed at the cell surface or secreted by the cell.
