Accumulation of cytolytic CD8 T cells in B16-melanoma and proliferation of mature T cells in TIS21-knockout mice after T cell receptor stimulation

In vivo and in vitro effects of TIS21 gene on the mature T cell activation and antitumor activities were explored by employing MO5 melanoma orthograft and splenocytes isolated from the TIS21-knockout (KO) ² mice. Proliferation and survival of mature T cells were significantly increased in the KO than the wild type (WT) ³ cells, indicating that TIS21 inhibits the rate of mature T cell proliferation and its survival. In MO5 melanoma orthograft model, the KO mice recruited much more CD8⁺ T cells into the tumors at around day 14 after tumor cell injection along with reduced tumor volumes compared with the WT. The increased frequency of granzyme B⁺ CD8⁺ T cells in splenocytes of the KO mice compared with the WT may account for antitumor-immunity of TIS21 gene in the melanoma orthograft. In contrast, reduced frequencies of CD107a⁺ CD8⁺ T cells in the splenocytes of KO mice may affect the loss of CD8⁺ T cell infiltration in the orthograft at around day 19. These results indicate that TIS21 exhibits antiproliferative and proapoptotic effects in mature T cells, and differentially affects the frequencies of granzyme B⁺ CD8⁺ T-cells and CD107a⁺ CD8⁺ T-cells, thus transiently regulating in vivo anti-tumor immunity.