According to the present invention, HLA matching donor-originating activated lymphocytes highly effective in the treatment of patients with tumors, viral infections and autoimmune diseases are prepared by collecting cells contained in peripheral blood originating from an HLA matching donor or peripheral blood originating from an HLA matching donor achieving micro-chimerism and by stimulating and propagating the cells thus collected with, for instance, interleukin 2 and anti-CD3 antibodies or the like. The HLA matching donor-originating activated lymphocytes thus prepared can be administered to an HLA matching patient with a tumor, a viral infection or an autoimmune disease for therapeutic or preventive purposes.