Abstract: This invention is directed to a method for assaying the degree of activation of immune cells by stimulating non-resting immune cells to activity with an intracellular-acting stimulant and then measuring the activity of the stimulated immune cells. The stimulant that can be used in this invention will effectively stimulate non-resting immune cells to activity, but will not effectively stimulate resting immune cells to activity. The stimulants that can be used in the invention of this assay act directly as activation probes. These stimulants can discern evidence of previous immune cell activation and will therefore effectively stimulate to activity primed immune cells. Since the stimulant discerns previous immune cell activation, the stimulants of this invention will not effectively stimulate to activity resting immune cells. The assay measurements can be used for a variety of evaluations, including correlating in vitro activity of ex vivo activated (EVA) with clinical outcome of the therapy with such cells.