Background  Tuftsin is an immunomodulator and has been certified to be able to inhibit tumor growth, whereas it is unstable in vivo with very short half-life period. T peptide is designed and developed as a new type of tuftsin derivative to extend its half-time, however, its anti-tumor effect and mechanism is still unclear.

  Objective  To investigate the anti-tumor effect and mechanism of T peptide.

  Methods  Female C57BL/6J mice aged 6–8 weeks were randomly divided into control group and T Peptide group with 6 mice in each group. A volume of 0.1 mL of B16-F10 cell suspension (5.0×10⁶ cells/mL) was inoculated subcutaneously under the right forelimb armpit of C57BL/6J mice on day 0. The mice in the T Peptide group were administrated with T Peptide subcutaneously at a dose of 8 mg/kg very other day, while the control mice were treated by the vehicle solution (normal saline) in the same way. The effect of T peptide on the growth of transplanted tumor was evaluated by measuring tumor weight. Flow cytometry was used to detect T lymphocytes (CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺, CD3⁺CD44⁺), natural killer cells (NK1.1⁺), myeloid-derived suppressor cells (CD11b⁺Gr-1⁺) and macrophages (F4/80⁺CD86⁺, F4/80⁺CD206⁺) both in mice spleens and at the transplanted tumor site. The expression of cytokines (IL-2, IL-4, IL-10, IL-12, TNF-α, TGF-β, IFN-γ) in the supernatant of spleen cells as well as in serum were determined by enzyme-linked immunosorbent assay. CCK-8 assay was employed to assess the in vitro cytotoxicity of T Peptide.

  Results  T Peptide did not have any influence on tumor cell proliferation in vitro, but showed an inhibitory effect on subcutaneously transplanted melanoma B16-F10 tumor in vivo, with the inhibition rate being 56.45%. For T Peptide treated tumor-bearing mice, the level of CD3⁺CD8⁺ T lymphocytes, M1 type macrophages (F4/80⁺CD86⁺), CD3⁺CD44⁺ T lymphocytes, and myeloid-derived suppressor cells (CD11b⁺Gr-1⁺) in the spleens increased significantly compared to the control group, while there was no significant change in M2 type macrophages (F4/80⁺CD206⁺) or natural killer cells (NK1.1⁺). In T peptide group, the number of CD3⁺CD44⁺ T lymphocytes at the tumor site increased significantly, whereas the in situ CD3⁺CD4⁺ T lymphocytes, CD3⁺CD8⁺ T lymphocytes, natural killer cells (NK1.1⁺), myeloid-derived suppressor cells (CD11b⁺Gr-1⁺) and macrophages (F4/80⁺CD86⁺, F4/80⁺CD206⁺) in grafted tumor did not show obvious difference between the two groups. Compared to the control group, the expression of cytokine IFN-γ both in the supernatant of spleen cell culture and in serum increased significantly in T peptide group, while the expression levels of IL-2, IL-4, IL-10, IL-12, TNF-α, and TGF-β did not show significant change.

  Conclusion  T peptide is noncytotoxic, it exerts anti-tumor effects by upregulation of CD8⁺ T cells, F4/80⁺CD86⁺ macrophages and IFN-γ in tumor-loaded mice.