Effects of IFN-gamma gene transfer on the immunogenicity of murine EMT6 mammary carcinoma cells

Abstract

The ability of specific cytokines to increase the immunogenicity of poorly or non immunogenic tumors is of extremely important clinical value because it can be exploited in the generation of an effective antitumor vaccine as a potential modality for treating cancer. In this scenario, the patient's tumor cells are transfected with the cytokine gene of interest, irradiated and re-injected into the patient as a vaccine with the potential of eliminating tumor recurrence or metastatic foci. Interferon-γ (IFNγ) is an important cytokine whose immunomodulatory properties include activation of immune cells and induction of class I and class II major histocompatibility complex antigens. Therefore IFNγ represents one of the most suitable candidates for a cytokine-transfected-tumor vaccine approach. In this study a retroviral vector was used to introduce the IFNγ gene into a murine mammary carcinoma cell line (EMT6), poorly responsive to exogenous IFNγ stimulation, to assess the effect of IFNγ transgene expression on tumor immunogenicity. Transductants expressed the IFNγ transgene, class II MHC antigens and secreted IFNγ. The induction of class 11 MHC in IFNγ-transduced cells correlated with expression of a mouse class II transactivator (CIITA), a cytoplasmic protein involved in the activation pathway of class II MHC gene. Whereas parental EMT6 cells grew unchecked, the growth of genetically modified tumor cells was inhibited in immunocompetent mice. Similar findings were demonstrated using an IFNγ gene-transduced melanoma cell line. Rechallenge of animals that rejected an IFNγ-transduced EMT6 clone with parental EMT6 cells resulted in tumor rejection, suggesting that IFNγ-transduced EMT6 cells were able to induce long term immunity. Vaccination of animals with low dose cytokine-transduced cells induced partial or complete protection against rechallenge with parental cells suggesting that significant clinical benefit may be achieved using a small fraction of cytokine-transduced cells as a vaccine. In addition, these studies demonstrated that the immunogenicity of tumor cells poorly responsive to exogenous IFNγ can be enhanced by inserting and expressing the IFNγ transgene. IFNγ-transduced cells expressing class 11 MHC may function as antigen by presenting cells presenting tumor associated antigens, suggesting a role for class II MHC in reducing EMT6 tumorigenicity and inducing long term tumor immunity.