Successful elimination of memory-type CD8⁺ T cell subsets by the administration of anti-Gr-1 monoclonal antibody in vivo

During investigating the expression of Gr-1 antigen on various subsets of mouse spleen cells, we found that Gr-1 was expressed on memory-type CD8 ⁺CD44^highCD62L^high T cells in addition to granulocytes. Intraperitoneal administration of anti-Gr-1 mAb caused almost complete elimination of Ly-6C⁺ memory-type CD8⁺ T cells as well as Ly-6G⁺ granulocytes. Anti-Gr-1 mAb-treated mouse spleen cells exhibited greatly reduced IFN-γ production in response to anti-CD3 mAb both in vitro and in vivo. This reduced cytokine production appeared to be derived from elimination of IFN-γ-producing Gr-1⁺CD8 ⁺ T cells. Indeed, CD8⁺ T cells with IFN-γ- producing activity and cytotoxicity were generated from isolated Gr-1 ⁺CD8⁺ cells but not from Gr-1^-CD8⁺ T cells. We also demonstrated that therapeutic effect of MBL-2 tumor-immunized spleen cells was greatly reduced by anti-Gr-1 mAb-treatment. Thus, we initially demonstrated that anti-Gr-1 mAb might become a good tool to investigate a precise role for memory-type CD8⁺ T cells in vivo.