IL-2 inhibits the induction of systemic antitumour immunity by IL-4 in the peritumoural treatment of experimental melanoma.

We have examined the relative abilities of interleukin-4 (IL-4) and interleukin-2 (IL-2) to inhibit the growth of the B.16 melanoma in C57BL/6 mice. Tumours were allowed to become established and then treated peritumourally with either IL-4 or IL-2, or a combination of IL-4 plus IL-2. Treatment was continued for 7 days and then the tumours were removed and weighed. The results showed that IL-4 strongly inhibited tumour growth in 83% of individuals, but complete resolution was observed in only 18%. In the IL-2 treated groups, the percentage of growth-inhibited tumours was markedly less (50%), with 14% complete resolutions. In the IL-4+IL-2 treated tumours resolution was again different, such that only 57% of tumours were smaller than those seen in the controls but there was a high number bearing no measurable tumour (25%). In addition, of the three treatments described, only peritumoural administration of IL-4 alone could mediate the induction of systemic protection from tumour growth. These results suggest that IL-4 and IL-2 have different mechanisms of action and that IL-2 may antagonise the effect of IL-4 such that the action of the two materials when combined is highly unpredictable.