INTERLEUKIN-2 EXPRESSION BY TUMOR-CELLS ALTERS BOTH THE IMMUNE-RESPONSE AND THE TUMOR MICROENVIRONMENT

Microenvironmental conditions within solid tumors can have marked effe cts on the growth of the tumors and their response to therapies. The d isorganized growth of tumors and their attendant vascular systems tend s to result in areas of the tumors that are deficient in oxygen (hypox ic). Cells within these hypoxic areas are more resistant to convention al therapies such as radiation and chemotherapy. Here, we examine the hypoxic state of EMT6 mouse mammary tumors and the location of host ce lls within the different areas of the tumors to determine whether such microenvironmental conditions might also affect their ability to be r ecognized by the immune system. Hypoxia within tumors was quantified b y flow cytometry and visualized by immunohistochemistry using a monocl onal antibody (ELK3-51) against cellular adducts of zol-1-yl)-N-(2,2,3 ,3,3-pentafluoropropyl)acetamide (EF5), a nitroimidazole compound that binds selectively to hypoxic cells. Thy-1(+) cells, quantified using a monoclonal antibody, were found only in the well-oxygenated areas. T he location of these Thy-1(+) cells was also examined in EMT6 tumors t hat had been transfected with the gene for interleukin-2 (IL-2) becaus e these tumors contain greatly increased numbers of host cells. Surpri singly, we found that IL-2-transfected tumors had significantly decrea sed hypoxia compared to parental tumors. Furthermore, using the fluore scent dye Hoechst 33342, an in vivo marker of perfused vessels, combin ed with immunochemical staining of PECAM-1 (CD31) as a marker of tumor vasculature, we found increased vascularization in the IL-2-transfect ed tumors. Thus, expression of IL-2 at the site of tumor growth may en hance tumor immunity not only by inducing the generation of tumor-reac tive CTLs but also by allowing increased infiltration of activated T c ells into the tumors.