Background Human leukocyte antigen-G (HLA-G) is an immune checkpoint molecule that belongs to the non-classical HLA-class I family of receptors. HLA-G restrains immune cell activation and effector function by engaging with inhibitory receptors ILT2 and ILT4. While expression of HLA-G is highly restricted under normal healthy conditions, we have demonstrated that its expression in cancer is aberrantly upregulated and broadly detected across a variety of tumor types. Tizona Therapeutics has generated a novel, fully human antibody that specifically targets HLA-G and reverses HLA-G-mediated immunosuppression. Here we present in vitro and in vivo data demonstrating the functional impact of HLA-G blockade on immune cells and evidence to support the use of TTX-080 in the clinic to treat patients with advanced solid tumors.
Methods Evaluation of HLA-G expression in cancer was performed using immunohistochemistry, flow cytometry, and gene profiling. Expression of ILT2 and ILT4 was assessed on tumor infiltrating leukocytes by flow cytometry. To demonstrate the suppressive function of HLA-G, primary human NK cells, T cells, and monocyte-derived macrophages were cultured with target cells expressing HLA-G. TTX-080 was then evaluated for its ability to reverse this suppression. In addition, TTX-080 was investigated in vivo using a disseminated xenograft tumor model.
Results Expression of HLA-G was detected on tumor cells and tumor infiltrating leukocytes across a variety of solid tumor types. TTX-080 blocked interaction of HLA-G with both ILT2 and ILT4 and restored cytotoxicity in multiple assays using either primary NK cells or NKL cell lines. Monocyte-derived macrophages expressing ILT2 and ILT4 exhibited decreased phagocytosis of HLA-G+ target cells; this inhibition was reversed with an antigen-binding fragment of TTX-080. TTX-080 was also able to reverse HLA-G-mediated suppression of ILT2+ CD8+ T cells as assessed by degranulation and proinflammatory cytokine secretion. Notably, mice with disseminated tumors had extended median survival when treated with a single dose of TTX-080.
Conclusions TTX-080 reverses HLA-G-mediated suppression of ILT2+ and ILT4+ immune cells that are found within the tumor microenvironment. Blockade of HLA-G using TTX-080 therefore has the potential to reverse broad immune suppression in patients with advanced solid tumors by reinvigorating CD8+ T cells, enhancing NK cytolytic activity, and increasing macrophage phagocytosis.
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