Large T Antigen-Specific Cytotoxic T Cells Protect Against Dendritic Cell Tumors through Perforin-Mediated Mechanisms Independent of CD4 T Cell Help.

Our newly generated murine tumor dendritic cell (MuTuDC) lines, generated from tumors developing in transgenic mice expressing the simian virus 40 large T antigen (SV40LgT) and GFP under the DC specific promoter CD11c, reproduce the phenotypic and functional properties of splenic wild type CD8α(+) conventional DCs. They have an immature phenotype with low co-stimulation molecule expression (CD40, CD70, CD80, and CD86) that is upregulated after activation with toll-like receptor ligands. We observed that after transfer into syngeneic C57BL/6 mice, MuTuDC lines were quickly rejected. Tumors grew efficiently in large T transgene-tolerant mice. To investigate the immune response toward the large T antigen that leads to rejection of the MuTuDC lines, they were genetically engineered by lentiviral transduction to express luciferase and tested for the induction of DC tumors after adoptive transfer in various gene deficient recipient mice. Here, we document that the MuTuDC line was rejected in C57BL/6 mice by a CD4 T cell help-independent, perforin-mediated CD8 T cell response to the SV40LgT without pre-activation or co-injection of adjuvants. Using depleting anti-CD8β antibodies, we were able to induce efficient tumor growth in C57BL/6 mice. These results are important for researchers who want to use the MuTuDC lines for in vivo studies.

Recruitment of Matrix Metalloproteinase-9 (MMP-9) to the Fibroblast Cell Surface by Lysyl Hydroxylase 3 (LH3) Triggers Transforming Growth Factor-β (TGF-β) Activation and Fibroblast Differentiation.

Solid tumor growth triggers a wound healing response. Similar to wound healing, fibroblasts in the tumor stroma differentiate into myofibroblasts (also referred to as cancer-associated fibroblasts) primarily, but not exclusively, in response to transforming growth factor-β (TGF-β). Myofibroblasts in turn enhance tumor progression by remodeling the stroma. Among proteases implicated in stroma remodeling, matrix metalloproteinases (MMPs), including MMP-9, play a prominent role. Recent evidence indicates that MMP-9 recruitment to the tumor cell surface enhances tumor growth and invasion. In the present work, we addressed the potential relevance of MMP-9 recruitment to and activity at the surface of fibroblasts. We show that recruitment of MMP-9 to the fibroblast cell surface occurs through its fibronectin-like (FN) domain and that the molecule responsible for the recruitment is lysyl hydroxylase 3 (LH3). Functional assays suggest that both pro- and active MMP-9 trigger α-smooth muscle actin expression in cultured fibroblasts, reflecting myofibroblast differentiation, possibly as a result of TGF-β activation. Moreover, the recombinant FN domain inhibited both MMP-9-induced TGF-β activation and α-smooth muscle actin expression by displacing MMP-9 from the fibroblast cell surface. Together our results uncover LH3 as a new docking receptor of MMP-9 on the fibroblast cell surface and demonstrate that the MMP-9 FN domain is essential for the interaction. They also show that the recombinant FN domain inhibits MMP-9-induced TGF-β activation and fibroblast differentiation, providing a potentially attractive therapeutic reagent toward attenuating tumor progression where MMP-9 activity is strongly implicated.