ovalbumin and Mesothelioma

We assessed the murine Stimulator of Interferon Genes (STING) agonist, DMXAA, for anti-mesothelioma potential using the AE17-sOVA model that expresses ovalbumin (OVA) as a neo tumor antigen. Dose response experiments alongside testing different routes of administration identified a safe effective treatment regimen that induced 100% cures in mice with small or large tumors. Three doses of 25mg/kg DMXAA given intra-tumorally every 9 days induced tumor regression and long-term survival (>5 months). Re-challenge experiments showed that tumor-free mice developed protective memory. MTT and propidium-iodide assays showed that DMXAA exerted direct cytotoxic effects at doses >1mg/ml on the murine AE17 and AB1 mesothelioma cell lines.

Topics: Animals; Antigen Presentation; Antigens, Neoplasm; Disease Models, Animal; Mesothelioma; Mesothelioma, Malignant; Mice; Ovalbumin; T-Lymphocytes, Cytotoxic

Cytotoxic chemotherapies may expose the immune system to high levels of tumor antigens and expand the CD8(+) T-cell response to include weak or subdominant antigens. Here, we evaluated the in vivo CTL response to tumor antigens using a murine mesothelioma tumor cell line transfected with a neotumor antigen, ovalbumin, that contains a known hierarchy of epitopes for MHC class I molecules. We show that as tumors progress, effector CTLs are generated in vivo that focus on the dominant epitope SIINFEKL, although a weak response was seen to one (KVVRFDKL) subdominant epitope. These CTLs did not prevent tumor growth. Cisplatin treatment slowed tumor growth, slightly improved in vivo SIINFEKL presentation to T cells and reduced SIINFEKL-CTL activity. However, the CTL response to KVVRFDKL was amplified, and a response to another subdominant epitope, NAIVFKGL, was revealed. Similarly, gemcitabine cured most mice, slightly enhanced SIINFEKL presentation, reduced SIINFEKL-CTL activity yet drove a significant CTL response to NAIVFKGL, but not KVVRFDKL. These NAIVFKGL-specific CTLs secreted IFNγ and proliferated in response to in vitro NAIVFKGL stimulation. IL-2 treatment during chemotherapy refocused the response to SIINFEKL and simultaneously degraded the cisplatin-driven subdominant CTL response. These data show that chemotherapy reveals weaker tumor antigens to the immune system, a response that could be rationally targeted. Furthermore, while integrating IL-2 into the chemotherapy regimen interfered with the hierarchy of the response, IL-2 or other strategies that support CTL activity could be considered upon completion of chemotherapy.

Topics: Animals; Antigen Presentation; Antigens, Neoplasm; Antineoplastic Agents; CD8-Positive T-Lymphocytes; Cell Line, Tumor; Cisplatin; Cytotoxicity, Immunologic; Deoxycytidine; Epitopes; Female; Gemcitabine; Histocompatibility Antigens Class I; Interferon-gamma; Interleukin-2; Mesothelioma; Mice; Mice, Inbred C57BL; Ovalbumin; T-Lymphocytes, Cytotoxic; Transfection

Therapeutic use of IL-2 can generate antitumor immunity; however, a variety of different mechanisms have been reported. We injected IL-2 intratumorally (i.t.) at different stages of growth, using our unique murine model of mesothelioma (AE17; and AE17 transfected with secretory OVA (AE17-sOVA)), and systematically analyzed real-time events as they occurred in vivo. The majority of mice with small tumors when treatment commenced displayed complete tumor regression, remained tumor free for >2 mo, and survived rechallenge with AE17 tumor cells. However, mice with large tumors at the start of treatment failed to respond. Timing experiments showed that IL-2-mediated responses were dependent upon tumor size, not on the duration of disease. Although i.t. IL-2 did not alter tumor Ag presentation in draining lymph nodes, it did enhance a previously primed, endogenous, tumor-specific in vivo CTL response that coincided with regressing tumors. Both CD4(+) and CD8(+) cells were required for IL-2-mediated tumor eradication, because IL-2 therapy failed in CD4(+)-depleted, CD8(+)-depleted, and both CD4(+)- and CD8(+)-depleted C57BL/6J animals. Tumor-infiltrating CD8(+) T cells, but not CD4(+) T cells, increased in association with a marked reduction in tumor-associated vascularity. Destruction of blood vessels required CD8(+) T cells, because this did not occur in nude mice or in CD8(+)-depleted C57BL/6J mice. These results show that repeated doses of i.t. (but not systemic) IL-2 mediates tumor regression via an enhanced endogenous tumor-specific CTL response concomitant with reduced vasculature, thereby demonstrating a novel mechanism for IL-2 activity.

Topics: Adjuvants, Immunologic; Animals; Antigen Presentation; Antigens, CD; Antigens, Neoplasm; Antineoplastic Agents; B7-2 Antigen; CD4-Positive T-Lymphocytes; CD8-Positive T-Lymphocytes; Cell Death; Cell Division; Cell Line, Tumor; Cytotoxicity, Immunologic; Egg Proteins; Female; Graft Rejection; Growth Inhibitors; Histocompatibility Antigens Class I; Immunodominant Epitopes; Immunotherapy, Active; Injections, Intralesional; Injections, Intraperitoneal; Interleukin-2; Lymphocytes, Tumor-Infiltrating; Membrane Glycoproteins; Mesothelioma; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Nude; Mice, Transgenic; Necrosis; Neoplasm Transplantation; Neovascularization, Pathologic; Ovalbumin; Peptide Fragments; Survival Rate; T-Lymphocyte Subsets