T cells having a desired antigen specificity are stimulated by (a) introducing immortalizing genes into antigen-presenting cells in a manner permitting regulation of the expression and/or function of at least one of these genes to achieve conditionally immortalized antigen-presenting cells; (b) introducing a gene encoding the desired antigen into the immortalized cells in a manner permitting the antigen to be expressed after the expression and/or abolishment of the function of at least one of the immortalizing genes stops; (c) expanding the immortalized antigen-presenting cells by expression and/or functional activation of the immortalizing genes; (d) completing the proliferation of the immortalized antigen-presenting cells by stopping the expression and/or abolishing the function of at least one of the controllable immortalizing genes; (e) continuing the expression of the antigen; (f) adding leucocytic cells including T cells and cultivating the cell mixture to stimulate the T cells directed against the desired antigen; and (g) optionally purifying and isolating the stimulated T cells.