EFFECTS OF IL-3 GENE-EXPRESSION ON TUMOR RESPONSE TO IRRADIATION IN-VITRO AND IN-VIVO

Expression of a murine interleukin 3 gene in murine fibrosarcoma cells (FSA-JmIL-3) did not alter their survival after in vitro irradiation, However, FSA-JmIL-3 tumors established in vivo were much more sensiti ve to irradiation than was the parental tumor. Following 25 Gy of irra diation, parental fibrosarcoma tumors regrew after a growth delay of 1 0 days, but FSA-JmIL-3 tumors continued to regress, Examination of the cellular composition of tumors following irradiation revealed that, i nstead of tumor cell repopulation, the FSA-JmIL-3 tumors became heavil y infiltrated with lymphocytes, indicating that the effect of irradiat ion was to allow the IL-3-elicited cellular immune response to infiltr ate the tumors and mediate rejection, This study indicates that combin ing gene immunotherapy approaches with radiotherapy might increase the effectiveness of both, and it seems logical to pursue such treatment options.