GENE-TRANSFER OF A HYBRID INTERLEUKIN-1-BETA GENE TO B16 MOUSE MELANOMA RECRUITS LEUKOCYTE SUBSETS AND REDUCES TUMOR-GROWTH IN-VIVO

Interleukin(IL)-1 differs from most other cytokines in its lack of a s ignal sequence. This results in intracellular retention of the immatur e preform. The release of IL-1 has been shown to be restricted predomi nantly to activated monocytes and macrophages and to be associated wit h apoptosis of the producer cell. These features have limited the inve stigation of IL-1 in early immune responses. In order to study the bio logical effects of local IL-1 beta release during an antitumour immune response, we used B16 mouse melanoma cells transduced with mature hum an IL-1 beta cDNA constructs. To obtain a released form of human IL-1 beta (ssIL-1 beta), the signal sequence from the related IL-1 receptor antagonist was ligated to the cDNA that encoded the mature form of IL -1 beta. When cells of the poorly immunogenic B16 melanoma cell line w ere transduced with IL-1 beta by retroviral infection, high levels of the protein were detected intracellularly, whereas cells transduced wi th IL-1 beta containing the signal sequence secreted most of their pro tein. The in vitro growth of the melanoma cells was unaffected by the IL-1 beta or ssIL-1 beta gene transfer. In contrast, the in vivo subcu taneous tumour growth of the ssIL-1 beta-transduced B16 cells in synge neic C57BL/6 mice was significantly reduced compared with the IL-1 bet a- and the mock-transduced controls. Immunohistochemical analysis reve aled the infiltration of macrophages to be strong in B16/ssIL-1 beta, moderate in B16/IL-1 beta and minimal in control tumours. Furthermore, a moderate infiltration of CD4(+) cells and of scattered dendritic ce lls was detected in B16/ssIL-1 beta rumours whereas very few or no CD4 (+) cells and dendritic cells were seen in the B16/IL-1 beta or contro l tumours. Following in vivo growth, all the tumours upregulated ICAM- 1 on their cell surfaces. However, the percentage of ICAM-1-expressing cells was two- to four-fold higher in B16/ssIL-1 beta rumours compare d ro the control. The data suggest that IL-1 beta acts in vivo, either directly or indirectly, as a chemotactic factor for monocytes, T help er cells and dendritic cells. This supports IL-1 beta having a regulat ory effect on tumour growth when locally released in the tumour area.