Human CD8⁺CD28^- T suppressor cells expanded by common gamma chain (γc) cytokines retain steady allospecific suppressive capacity in vivo

Background: CD8⁺CD28^- T suppressor (Ts) cells play critical role in transplant tolerance. Our previous study has generated CD8⁺CD28^- Ts cells in vitro which exert robust allospecific suppressive capacity in vitro.

Results: CD8⁺CD28^- Ts cells were expanded by stimulating human CD8⁺ T cells with allogeneic antigen presenting cells in the presence of the common gamma chain cytokines IL-2, IL-7 and IL-15 in vitro, and were further verified in vitro through day 7 to 11 for their persistency of the allospecific suppressive capacity. When CD8⁺CD28^- Ts cells were adoptively transferred into NOG mice, their capacity to inhibit CD4⁺ T cell proliferation in allospecific manner remained potent on 11 days after their injection. The mechanisms for expansion of CD8⁺CD28^- Ts cells by the common gamma chain cytokines were investigated. These included promoting CD8⁺CD28^- T cells proliferation, converting CD8⁺CD28⁺ T cells to CD8⁺CD28^- T cells and decreasing CD8⁺CD28^- T cell death. Furthermore, the expanded CD8⁺CD28^- Ts cells showed upregulation of the co-inhibitory molecule Tim-3 and down-regulation of the cytotoxic molecule granzyme B.

Conclusions: In summary, these results demonstrated that the in vitro-expanded human CD8⁺CD28^- T cells retained potent allospecific suppressive capacity in vivo and depicted multiple mechanisms for the expansion of Ts cells, which might promote further bench to clinic research.