Hepatoma cells inhibit the differentiation and maturation of dendritic cells and increase the production of regulatory T cells

Tumor cells may escape from the immune responses because of defective differentiation of dendritic cells (DC). Recent studies have found an increased number of regulatory T cells (Treg) in both peripheral blood and tissues from patients with hepatocellular carcinoma. In the present study, we used tumor culture supernatants (TSN) from hepatoma-derived cell lines to investigate whether TSN interfere with the differentiation of human monocyte-derived DC and/or their ability to increase Treg. The results showed that exposure to TSN significantly inhibited the differentiation of monocytes into DC with retained CD14 molecule and reduced expression of CD1a. These TSN-exposed immature DC also produced significant amount of immunosuppressive cytokine IL-10 and displayed an increased expression of co-stimulatory molecules. Upon stimulation with LPS, however, the TSN-exposed DC failed to undergo full maturation, with a blockage of the upregulation of co-stimulatory molecules on their surface and a switch to an IL-10highIL-12lowTNF-αlow phenotype. Moreover, exposure of DC to TSN selectively inhibited their capacity to stimulate the proliferation of allogeneic CD8+ T cells, but promoted the generation of CD4+CD25hiFoxp3+ Treg cells. These findings, together with previous clinical studies showing that CD4+CD25hi Treg cells are concentrated within hepatocellular carcinoma tissue, suggest that the local tumor microenvironment may favor the induction of Treg cells through inhibiting the differentiation and maturation of DC.