Devil Facial Tumour Disease: In vivo studies in mice

Devil Facial Tumour Disease (DFTD) is an infectious cancer cell line transmitted as an allograft between Tasmanian devils. On transmission it does not evoke an immune response, is 100% fatal and is driving the Tasmanian devil towards extinction in the wild. Due to their endangered status, access to Tasmanian devils to study DFTD is limited. As a consequence this study of DFTD was undertaken in mice to complement studies being done in Tasmanian devils. Inoculation of immunocompetent mice with DFTD cells did not result in DFTD tumour establishment. This rejection was a specific immune response because DFTD specific antibodies were produced. This provided evidence that DFTD cells are immunogenic and susceptible to killing by the immune system making them suitable targets for immunotherapy and vaccines. Immunocompetent mice also provided a model to study immunogenicity of various DFTD cell preparations and injection protocols applicable to vaccine development. For example, 14 day prime-boost intraperitoneal injections of DFTD cells resulted in enhanced antibody and cytokine responses in mice compared to subcutaneous injections. Inactivation of DFTD cells by freeze-thawing or sonication reduced the immunogenicity of DFTD cells while irradiation of DFTD cells maintained immunogenicity. NOD/SCID mice have severe immune system defects that prevented protective immune responses against DFTD cells allowing tumours to establish. Consequently, these mice provided a xenograft model to study aspects of DFTD that could not be replicated in an in vitro setting. This included DFTD establishment and growth as well as efficacy of adoptive cell transfer trials. Adoptive cell transfer from immunocompetent mice conferred protection against DFTD as did adoptive transfer of Tasmanian devil lymphokine activated killer (LAK) cells. In this context, LAK cells refer to lymphocytes which have been stimulated in vitro with mitogens or cytokines to induce non-specific activated killer cells capable of killing DFTD cells without harming normal cells. The xenograft model also facilitated the evaluation of the chemotherapeutic agents afatinib, withaferin A and imiquimod. The most promising results came from intratumoural injections of imiquimod which caused the upregulation of ˜í‚â§2-microglobulin on the surface of the DFTD cells. DFTD cells avoid immune recognition in Tasmanian devils because they do not express MHC on the cell surface. Upregulation of ˜í‚â§2-microglobulin indicates that MHC was upregulated. This has important implications for the Tasmanian devil as the MHC would make the DFTD cells visible to the Tasmanian devil's immune system and this should invoke protective immune responses. In conclusion, DFTD cells are immunogenic and can be targeted by antibodies and cytotoxic cells. This makes them suitable candidates for vaccines or immunotherapy in Tasmanian devils. They avoid the Tasmanian devils immune system by downregulating MHC. This ignorance can be overcome by non-specific activation of LAK cells capable of killing DFTD cells in a MHC independent manner. The tumour cells can be targeted by imiquimod to upregulate surface molecules including ˜í‚â§2-microglobulin and MHC to make them more immunogenic and potential targets for MHC dependent cytotoxic responses.