Effect of local interleukin-2 treatment on spontaneous tumours of different immunogenic strength

Transplantable tumour lines established from spontaneous tumours of BALB/c, CBA, and DBA/2 mice displayed different immunogenic strength. This report describes tumour susceptibility to interleukin-2 (IL-2) therapy in relation to tumour immunogenicity. The following tumour lines were used: X5, X6, an d X9 mammary tumours of DBA/2, BALB/c, and CBA origin respectively, X7 carc inoma of BALB/c and X18 papilloma of CBA mice. Two spontaneous tumours of l ong transplantation history, SL2 lymphoma (SL2) of DBA/2 and Madison lung c arcinoma M109 (M109) of BALB/c origin, were used as control systems. Experi mental mice were transplanted with different inocula of tumour cells at day 0; treatment with IL-2 was initiated on days 1-3 or delayed until day 10 a nd consisted of daily injections of low doses of 5000 or 20000 U/mouse give n five times a week for a period of 3 weeks. Treatment of SL2 (2 x 10(4) ce lls injected i.p.) consisted of i.p. injections of 5000 or 20000 U IL-2/mou se given on days 10-14 after tumour transplantation. IL-2 therapy of SL2-be aring DBA/2JIco mice resulted in a significant proportion of cures; however , no response to IL-2 treatment was achieved in SL2-bearing DBA/2CrIiw 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 five sponta neous tumours resulted, in general, in transient growth inhibition of the i .m. transplants of lines X5, X6, and X7 provided that IL-2 was administered locally. The therapeutic effect depended on the number of transplanted tum our cells, the best results being achieved at cell numbers close to the dos e-inducing tumour growth in 50% of animals. We found that the spontaneously arising tumours responding to IL-2 treatment were all slowly growing and i mmunogenic (X6 and X7) or might have viral association (X5) and, as such, m ight express foreign antigens. The data suggest a correlation between tumou r immunogenicity and the therapeutic effect. However, IL-2 can still exert some effect against tumours with negligible immunogenicity.