Effective cytokine gene therapy against an intracranial glioma using a retrovirally transduced IL-4 plus HSVtk tumor vaccine

To explore the potential for molecular immunotherapies in the treatment of malignant gliomas, we evaluated the efficacy of subcutaneous tumor cell vac cines in the treatment of intracranial 9L tumors, using 9L gliosarcoma cell lines stably transduced with the murine interleukin-4 cDNA (9L-IL4), the h erpes simplex virus-thymidine kinase cDNA (9L-Tk) or both (9L-IL4-Tk). The expression of multiple genes from a single transcript was achieved by incor porating internal ribosomal entry site (IRES) cassettes in the retroviral c onstructs. Subcutaneous immunization of rats with nonirradiated 9L-IL4 cell s or 9L-IL4-Tk cells followed by treatment with ganciclovir (GGV) completel y protected the animals from a subsequent intracranial challenge with wildt ype 9L cells. In contrast, only 50% of animals immunized with SL-Tk cells a nd 0% of SL-neo immunized animals rejected the same challenge with wild-typ e 9L. More importantly, treatment of established (day 3) intracranial 9L tu mors with genetically engineered tumor cells resulted in long-term survival (> 100 days) for 25-43% of 9L-IL4-Tk immunized animals and for 27% of noni rradiated 9L-IL4 immunized animals, in striking contrast no SL-Tk, SL-neo o r irradiated 9L-IL4 immunized animals survived for more than 33 days. As a marker of a cellular immune response, splenocytes from nonirradiated 9L-IL4 , SL-Tk or 9L-IL4-Tk immunized animals produced interferon-gamma (IFN-gamma ) in greater amounts than those from SL-neo immunized or Hank's balanced sa lts solution (HBSS) treated animals when stimulated with wild-type 9L in vi tro. Our findings support the use of tumor cell vaccines expressing the IL- 4 and HSVtk genes for the treatment of malignant gliomas.