Abstract
Cancer cells can evade host immune systems via multiple mechanisms. Transforming growth factor beta 1 (TGF-β1) is an immunosuppressive cytokine that induces regulatory T cell (Tregs) differentiation and is involved in immune evasion mechanisms in cancer. The inhibition of the TGF-β1 signaling pathway can suppress cancer progression and metastasis through the modulation of anticancer immune responses. However, to best of our knowledge, no implementation of treatments targeting TGF-β1 has been reported in dog cancers. This study aimed to examine whether TGF-β1 is upregulated in canine cancers. We measured TGF-β1 concentrations in culture supernatants of canine melanoma cell lines and in serum samples from dogs with oral malignant melanoma. TGF-β1 production was observed in several cell lines, and serum TGF-β1 levels were elevated in dogs with oral malignant melanoma. Interestingly, the addition of recombinant TGF-β1 to canine peripheral blood mononuclear cell cultures decreased Th1 cytokine production and increased differentiation of CD4+CD25+Foxp3+ lymphocytes, suggesting that TGF-β1 is immunosuppressive in canine immune systems. We developed a decoy receptor for TGF-β, namely TGF-βRII-Ig, by identifying an open reading frame of the canine TGFBR2 gene. TGF-βRII-Ig was prepared as a recombinant fusion protein of the extracellular region of canine TGF-βRII and the Fc region of canine IgG-B. As expected, TGF-βRII-Ig bound to TGF-β1. In the presence of TGF-β1, the treatment with TGF-βRII-Ig increased Th1 cytokine production and decreased the differentiation of CD4+CD25+Foxp3+ lymphocytes. Our results suggest that TGF-βRII-Ig competitively inhibits the immunosuppressive effects of TGF-β1 and thereby activates immune responses. This study demonstrated the potential of TGF-βRII-Ig as a novel biologic for canine melanoma.
Highlights
Transforming growth factor beta 1 (TGF-β1) is a multifunctional cytokine that is associated with cancer progression and suppression of immune response [1, 2]
We examined the potential of TGF-β1 as a therapeutic target in canine melanoma by confirming TGFβ1 production in melanoma cell lines and evaluating TGF-β1 serum concentrations in dogs with oral malignant melanoma (OMM)
The decoy receptor TGF-βRII-Ig bound to TGF-β1 and reversed cytokine production and Tregs differentiation induced by TGF-β1
Summary
Transforming growth factor beta 1 (TGF-β1) is a multifunctional cytokine that is associated with cancer progression and suppression of immune response [1, 2]. TGF-β1 directly inhibits cytotoxic T cell function by suppressing cell proliferation and the expression of cytotoxic genes [3, 4]. TGF-β1 inhibits the effector function of natural killer cells [5], contributing to immune evasion of cancer cells [6]. TGF-β1 indirectly mediates immunosuppression by inducing regulatory T cells (Tregs) from peripheral naive T cells [7]. Tregs inhibit interleukin (IL)-2 competitively through the increased expression of the IL-2 receptor, CD25, and suppress T cell function by producing immunosuppressive cytokines such as IL10 and TGF-β1 [8]. TGF-β1 is considered a critical suppressor of Th1 responses in normal and diseased conditions, including cancers
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