Therapeutic potential of biological response modifiers against transplantable mouse tumors of spontaneous origin. II. Local interleukin 2 treatment of tumors of different immunogenic strength.

This report describes tumor susceptibility to interleukin 2 (IL-2) therapy in relation to tumor immunogenicity. The following lines recently established from spontaneous tumors were used: X5, X6, and X9 mammary tumors of DBA/2, BALB/c and CBA origin, respectively, X7 carcinoma of BALB/c and X18 papilloma of CBA mice. Two spontaneous tumors of long transplantation history, SL2 lymphoma (SL2) of DBA/2 and M109 Madison lung carcinoma (M109) of BALB/c origin, were used as control systems. Mice were transplanted with different inocula of tumor cells at day 0; IL-2 treatment was initiated on day 1-3 or 10 and consisted of daily injections of 5000 or 20,000 IU/mouse given 5 times a week for 3 weeks. SL2 (i.p. - 2 x 10(4) cells) treatment consisted of i.p. injections of 5000 or 20,000 IU IL-2 given on days 10-14. IL-2 therapy of SL2 bearing DBA/2JIco mice resulted in the significant proportion of cures; however, no response to IL-2 treatment was achieved in SL2 bearing DBA/2Crliw mice. BALB/c mice with the i.p. transplant of M109 responded to IL-2 treatment with 40% increase in lifespan. The low-dose IL-2 therapy of the 5 recently established tumors resulted, in general, in transient growth inhibition of the i.m. transplants of line X5, X6, and X7 provided IL-2 was administered locally. The therapeutic effect depended on the number of transplanted tumor cells, and the best results being achieved at cell numbers close to the dose inducing tumor growth in 50% of animals (TD50). We found that the tumors responding to IL-2 treatment were all slowly growing and immunogenic (X6 and X7) or might have viral association (X5) and as such might express foreign antigens.