Abstract
Transforming growth factor-beta (TGF-β) pathway mediates suppression of antitumor immunity and is associated with poor prognosis in triple-negative breast cancer (TNBC). In this study, we generated a humanized animal model by transplanting human peripheral blood mononuclear cells into immunodeficient mice followed by inoculation of MDA-MB-231 cells and subsequently analyzed the role of TGF-β2 in the interaction between human T cells and human tumor cells. Following reconstitution of the human immune system, inhibition of TGF-β signaling by TGF-β2 antisense oligodeoxynucleotide (TASO) resulted in accelerated tumor growth inhibition. TGF-β2 inhibition also resulted in downregulation of peripheral Foxp3 + regulatory T cells (Treg), whereas no effect was seen in the expression of CD8 + cytotoxic T cells. Analysis of the TASO-treated mice serum revealed elevated levels of human IFN-γ and reduced levels of human IL-10 and TGF-β2. Moreover, TGF-β2 inhibition resulted in increased CD8 + T cell infiltration, whereas the reduced infiltration of Tregs into the tumor partly resulted from decreased expression of CCL22. Decreased intratumoral Tregs facilitated the activation of cytotoxic T cells, associated with increased granzyme B expression. These results indicate that TASO potentiated T cell-mediated antitumor immunity, and it is proposed that TGF-β2 may be a promising target in the immunotherapeutic strategy of TNBC.