γδ T cells in hepatocellular carcinoma patients present cytotoxic activity but are reduced in potency due to IL-2 and IL-21 pathways.

ABSTRACT

Hepatocellular carcinoma (HCC) is the most common primary liver carcinoma and has one of the highest mortality rates of all cancers. The γδ T cells could infiltrate HCC and have demonstrated potent tumor-killing capacity. Here, we found that in peripheral blood, the vast majority of γδ T cells were Vδ2 T cells. In HCC patients, the frequency of Vδ2 T cells was significantly lower than in controls. γδ T cells that were harvested directly ex vivo possessed very limited capacity to eliminate Zol-loaded HCC cell lines, even at a high effector to target ratio. In vitro expansion with Zol could significantly increase the capacity of γδ T cells to eliminate HCC cell lines. But even with in vitro expansion, the γδ T cells from HCC patients presented significantly lower cytotoxic capacity than the γδ T cells from healthy individuals. The expression of IL-2 and IL-21 by γδ T cells was significantly lower in HCC patients than in control volunteers. Supplementing recombinant human IL-2 and IL-21 in the in vitro expansion culture increased the cytotoxic capacity of γδ T cells. In addition, the frequency of PD-1+ γδ T cells was significantly higher in HCC patients than in controls ex vivo, and was significantly elevated after in vitro expansion. Hep3B and HepG2 did not express PD-L1, while a small fraction of SNU-398 expressed PD-L1. Interestingly, co-incubation with γδ T cell elevated PD-L1 expression in HCC cell lines. Blocking PD-1 during in vitro expansion stage significantly elevated cytotoxicity toward all the HCC cell lines, while blocking PD-1 during the cytotoxicity assay significantly elevated cytotoxicity toward HepG2 and SNU-398, but not toward Hep3B. Overall, these results demonstrated that the circulating γδ T cells in HCC patients were reduced in cytotoxic capacity, possibly associated with the lack of IL-2 and IL-21 production and PD-1 upregulation.