Polyinosinic-polycytidylic Acid Mediates PD-1 Expression in T Cells at Early Stage of Activation and Inhibits Melanoma Growth

Objective To investigate the expression level of programmed cell death protein 1 (PD-1) in T cells at the early stage of activation (T cells remained in spleen, before migration to target organ).

Methods C57BL/6 mice (6-8 weeks old) were immunized with Poly I:C peptide vaccine after randomly grouping. Mice spleen cells were harvested 7 days after immunization. The effects of Poly I:C on the activation of antigen specific or nonspecific T cells were evaluated. PD-1 expression on the antigen specific CD8⁺T cells was also detected. Furthermore, correlation between the anti-tumor effects of Poly I:C and CD8⁺T cells was assessed by CD8 cell knockout.

Results Poly I:C significantly promoted the activation of antigen specific or nonspecific T cells in mice spleens. Although antigen specific T cells increased the expression of PD-1, they could still synthesize IFN-γ, a T cell functional marker. Meanwhile, Poly I:C significantly inhibited the growth of melanoma in vivo (P=0.0243), which was correlated with CD8⁺T cells.

Conclusion Poly I:C could promote the activation of T cells; although, T cells at the early stage of activation (remained in spleen) enhanced the expression of PD-1, they are still functional.