Described are compositions and methods for detecting or monitoring the ability of an individual to mount a cell mediated immune response to a target antigen. Methods rely in part upon the physical association, e.g., by fusion, of a Lethal Factor (LF) polypeptide with a target antigen. The LF polypeptide moiety, including, for example, an LFn polypeptide moiety, serves as a transport factor to deliver target antigens, including full length target polypeptides, to the cytosol of an intact, living immune cell from an individual. Measurement of a cytokine response by the immune cell from the individual provides a read out of a cell mediated immune response. The methods and compositions described provide diagnostic as well as prognostic information and can guide the direction of therapy.