Objective: To observe the anti-tumor effect of suppressors of cytokine signaling 1(SOCS1)-silenced dentritic cell (DC) vaccines in melanoma-bearing mice, and the influence of IL-10 in the tumor microenvironment on DC vaccine action.
Methods: To obtain SOCS1-silenced DCs, DCs derived from mouse bone marrow cells ex vivo were induced to differentiation in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4, and then transduced with Len-SOCS1-shRNA or control Len-GFP lentiviruses. The SOCS1-silenced DCs were loaded by TRP2 peptide to prepare the DC vaccine, which was induced to mature by LPS. The DCs were analyzed by flow cytometry (FCM) for surface expressions of MHCII and CD86 and by real-time PCR for the expressions of SOCS1, IL-10 as well as IL-12p40. B16 or IL-10-silenced B16 (IL-10(-/-);) cells were inoculated into C57BL/6 mice. Five days later, the mice were randomly divided into 3 groups (PBS-DC, Len-DC and SOCS1-shRNA-DC groups) and injected with 1×10⁶;/100 μL per mouse of the transduced DCs or PBS-DCs. We observed the tumor growth and the survival of the tumor-bearing mice. Tumor-infiltrating leukocytes (TIL) were isolated from tumor tissues using the discontinuous gradient centrifugation and the distribution of CD8⁺;T was analyzed by FCM; IFN-γ secretion and CTL activity were detected by the ELISpot and the standard microcytotoxicity assay, respectively.
Results: SOCS1 expression in DCs was down-regulated by 80% after Len-SOCS1-shRNA lentivirus infection. In the DCs with down-regulated SOCS1 expression, the expressions of MHCII and CD86 increased a little, which did not differ significantly from the control DCs, and IL-10 level dropped and IL-12p40 went up significantly compared with the control DCs. There was no any effect of SOCS1-silenced DCs on the survival of melanoma-bearing mice, however, the survival of B16-IL-10(-/-);-bearing mice was promoted(P<0.05). The further investigation showed that SOCS1-shRNA DCs raised the number of CD8⁺;T lymphocytes, promoted the TRP2-specific IFN-γ production and CTL responses in B16-IL-10(-/-);-bearing mice.
Conclusion: The activity of the DC vaccine could be enhanced by silencing SOCS1 expression; however, the anti-tumor activity of SOCS1-silenced DC vaccine could be inhibited by IL-10 in tumor microenvironment.