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+CD44highCD62Lhigh 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.