A device for activating light-induced rupture of endocytic vesicles in target cells of a patient so as to effect delivery of an administered antigen to cytosol in the target cells, is described. The device is adapted to be worn by a patient over a region of skin where an antigen and a photosensitising agent are to be administered. The device comprises a rear surface that is rounded or otherwise configured to be worn against the patient's skin. It has a retaining part for retaining the device in place over the region of the patient's skin during an activation cycle. A light source is arranged to illuminate the patient's skin from the rear of the device. A control system is configured to vary the output of the light source with respect to time in accordance with a pre-configured output sequence.
