Induction of antitumor immunity by combined immunogene therapy using IL-2 and IL-12 in low antigenic Lewis lung carcinoma

Interleukin-2 (IL-2) and interleukin-12 (IL-12) are crucial cytokines that induce potent antitumor responses in a variety of animal cancer models. Alt hough single gene transfer of either IL-2 or IL-12 exhibits limited antitum or effects, the combination of IL-2 and IL-12 has been shown to induce a st ronger antitumor response and to cure tumor-bearing mice. To examine the co nditions necessary for tumor rejection, we varied the local concentration o f IL-2 and IL-12 by introducing these genes into Lewis lung carcinoma (LLC) cells via retroviral vectors and/or an adenoviral vector and evaluated the growth of inoculated LLC cells (5 x 10(5) cells). in contrast to the resul t when using a stepwise dose increase of IL-2 either without or with a fixe d production of IL-12 (4-5 ng/5 x 10(5) cells/24 hours, insufficient for tu mor rejection by itself), rejection of the tumor was achieved in 75% of the mice when the IL-12 secretion was combined with high and transient IL-2 pr oduction (42 ng/5 x 10(5) cells/24 hours) using additional adenoviral vecto r transduction (100 multiplicities of infection). An abundant infiltration of both CD4(+) (47.4/mm(2)) and CD8(+) (85.6/mm(2)) T cells was a character istic finding in the dual gene-transfected LLC tumors. Importantly, consist ent with the rejection of rechallenged parental cells, tumor-specific cytot oxic T lymphocytes were induced only from the splenocytes of mice inoculate d with the dual gene-transduced LLC cells, suggesting the existence of prot ective antitumor memory. In addition, only Vaccination of dual gene-transdu ced LLC cells inhibited the growth of pre-established LLC tumors. These res ults indicate that generation of a pivotal antitumor response likely depend s on the synergistic combination and concentration of IL-2 and IL-12 in the local milieu by which tumor specific immune memory is established.