Characterization of human lung tumor-associated fibroblasts and their ability to modulate the activation of tumor-associated T cells
Nazareth, Michael Ralph
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The tumor microenvironment of human non-small cell lung cancer (NSCLC) is composed largely of stromal cells, including fibroblasts, yet these cells have been the focus of few studies. Here, we established stromal cell cultures from primary NSCLC through isolation of adherent cells. Characterization of these cells by flow cytometry demonstrated a population which expressed a human fibroblast-specific 112-kd surface molecule, Thy1/CD90, α-SMA, and FAP, but failed to express CD45 and CD11b/Mac-1, a phenotype consistent with that of an activated myofibroblast. These cells, referred to here as tumor-associated fibroblasts (TAF), were found to express B7H1 (PD-L1) and B7DC (PD-L2) constitutively on their surface, and this expression was upregulated by IFN-γ. Several human non-small cell lung tumor cell lines also expressed B7H1 and B7DC, and some also expressed other B7 family co-regulatory molecules such as B7H2 and B7H4. It was also determined that TAF constitutively produce a number of proinflammatory cytokines and chemokines, including IFN-γ, IFN-ß, MIG, IP-10, RANTES, and TGF-ß1. TAF production of these biologically active factors and expression of regulatory surface molecules, provide multiple opportunities for the TAF to influence cellular interactions within the tumor microenvironment. To evaluate the ability of TAF to modulate tumor-associated T cell (TAT) activation, we conducted co-culture experiments between autologous TAF and TAT. In five out of eight tumors, TAF elicited a contact-dependent enhancement of TAT activation, even in the presence of a TGF-ß1-mediated suppressive effect. The contact-dependent enhancing response is MHC restricted, since the addition of blocking antibodies against MHC Class I or MHC Class II inhibited the TAF-mediated enhancing effect. In the three other tumors, TAF suppressed TAT activation, and, in one of these cases, blockade of B7H1 or B7DC was able to completely reverse the TAF-mediated suppression. This indicates that TAF expression of B7 family co-regulatory molecules is a potential mechanism by which TAF can regulate TAT activation within the tumor microenvironment. We conclude that TAF in human NSCLC provide multiple complex regulatory signals that have the potential to influence TAT quiescence and activation in the human non-small cell lung tumor microenvironment.