A method for producing immortalized antibody-secreting cells, comprising: (a) providing a transgenic animal having antibody-secreting cells capable of expressing one or more transgenes, wherein the antibody-secreting cells are in a non-immortalized state in the absence of a stimulus and are capable of changing to an immortalized state by means of the transgene or transgenes upon exposure of the cells to the stimulus; (b) extracting the antibody-secreting cells from the animal; and (c) exposing the antibody-secreting cells to the stimulus, thereby immortalizing the antibody secreting cells by means of the transgene or transgenes.