Disclosed herein are compositions for conferring oral tolerance in mammals to autoimmune disorders such as diabetes, as well as vectors and methods for plastid transformation of plants to produce a CTB-Pins protein for oral delivery. The invention also extends to the transformed plants, plant parts, and seeds and progeny thereof. The invention is applicable to plants edible without torrefying. Exemplified herein is the stable transformation of Lactuca sativa such that CTB-Pins is expressed.