NKT and CD8 lymphocytes mediate suppression of hepatocellular carcinoma growth via tumor antigen‐pulsed dendritic cells

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Abstract
Dendritic cells (DCs) are antigen presenting cells that play a role in T-cell activation. Liver-associated natural killer T lymphocytes (NKTs) are a unique subset of lymphocytes that may be important in antitumor immunity. Hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) expresses hepatitis B virus surface antigen (HBsAg) on its cell surface and may serve as a tumor-associated antigen. The aim of the study was to evaluate the antitumor effect of DC pulsed with tumor or viral-associated antigens in HBV-expressing HCC in mice and to determine the role of NKT lymphocytes in this process. Balb/c mice were sublethally irradiated and transplanted with Hep3b HCC cell line, followed by transplantation of naive splenocytes. DCs were separated using CD11c beads and pulsed with HBV-enveloped proteins (group A), HCC cell lysate (group B), or BSA (control group C). Mice were followed for survival and tumor size. To determine the mechanism of the antitumor effect, intrasplenic and intrahepatic lymphocyte subpopulations were analyzed by FACS for NKT, CD4 and CD8 markers. Tumor-associated antigens-specific IFNγ ELISPOT, T-cell proliferation assays and serum cytokine analysis were performed. Treatment with tumor-associated antigen-pulsed DC significantly improved survival (40% and 50% as compared with 0% in groups A, B, and control group C, respectively; p < 0.005). Tumor size decreased to 12.8 ± 0.4 and 0 from 60.4 ± 0.9 mm3 in groups A, B, and control group C, respectively (p < 0.005). Adoptive transfer of HBV or Hep3b-associated antigens-pulsed DC induced a 6-fold increase in peripheral CD8+ lymphocytes (from 1% in control mice to 6% and 5.5% in groups A and B, respectively), along with a decrease in CD4+ lymphocytes (from 3.5% in controls to 1.4% and 2.3% in A and B, respectively; p < 0.005). The CD8+/CD4+ ratio increased from 0.28 in controls to 4.28 and 2.39 in groups A and B, respectively (p < 0.005). Intrasplenic NKT cells increased from 7% in control mice to 7.98% and 14.6% in groups A and B, respectively. In contrast, an opposite shift was observed inside the liver. Intrahepatic lymphocyte analysis showed a marked increase in CD4+ and a decrease in CD8+ lymphocytes in treated groups. The intrahepatic CD4+ number increased from 0.5% in controls to 2.15% and 25.8% in groups A and B, respectively (p < 0.005). In contrast, a significant decrease in the intrahepatic CD8+ numbers was observed (from 7% in controls to 1.0% and 2.4% in groups A and B, respectively; p < 0.005). A significant increase was noted in HBV-specific IFNγ spot-forming T-cell colonies from 0.0 to 8.8 ± 1.7 and 1.8 ± 2.9 in groups C, A, and B, respectively (p < 0.005). Similarly, a significant increase in the HBV-specific T-cell stimulation index, from 0.8 ± 0.2 to 7.2 ± 0.4, in groups C and B, respectively, was noted (p < 0.002). IFNγ and IL12 serum levels increased significantly in treated groups. IFNγ and IL12 serum levels increased to 380 ± 30 and 400 ± 20, and 960 ± 40 and 760 ± 60 in groups A and B, compared with 150 ± 16 and 490 ± 40 pg/ml in control mice (p < 0.005). Tumor antigen-pulsed DCs effectively suppressed the growth of hepatocellular carcinoma in mice. This effect was associated with enhanced NKT and CD8+ lymphocyte function and augmentation of the antitumor/antiviral-specific IFNγ production.