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Immunosuppression mediated by regulatory T cells (Tregs) is a key facilitator of tumor immune evasion, but the source of these Tregs and their contribution to human cancer progression remains unclear. This study investigated the properties of FoxP3(+) Tregs, their prognostic value in patients with hepatocellular carcinoma (HCC) and the underlying mechanisms of FoxP3(+) Treg intratumoral accumulation. In addition to an increased number of circulating FoxP3(+) Tregs, the results also showed that FoxP3(+) Tregs gathered in the tumor site, where they suppressed tissue-derived CD4(+)CD25(-) T-cell activation (p < 0.001), promoting disease progression and poor prognosis in HCC patients (< 0.01). The intratumoral prevalence of FoxP3(+) Tregs was associated with a high density of macrophages (Mvarphi) (p < 0.001). Depletion of tissue Mvarphi thus attenuated the increase of liver FoxP3(+) Treg frequency attributed to in vivo inoculation with hepatoma (p = 0.01), whereas Mvarphi exposed to tumor culture supernatants from hepatoma-derived cell lines increased FoxP3(+) Treg frequency in vitro (p < 0.001). This increase was partially blocked by antiinterleukin-10 antibody (p < 0.01). In conclusion, tumor-associated Mvarphi may trigger a rise of the intratumoral FoxP3(+) Treg population, which in turn may promote HCC progression.
Zhou et al. (Mon,) studied this question.