Immunization with the amino-terminus region of dense granule protein 6 (GRA6) of Toxoplasma gondii activates CD8⁺ cytotoxic T cells capable of removing tissue cysts of the parasite through antigen presentation by human HLA-A2.1

CD8⁺ T cells from HLA-A2.1-transgenic mice, but not wild-type mice, immunized with the amino-terminus region (aa 41–152) of dense granule protein 6 (GRA6Nt) of Toxoplasma gondii secreted large amounts of perforin and granzyme B in response to GRA6Nt through antigen presentation by HLA-A2.1 in vitro. When those CD8⁺ T cells were transferred into chronically infected HLA-A2.1-expressing NSG mice deficient in T cells, cerebral cyst burden of the recipients of HLA-A2.1-transgenic T cells, but not of WT T cells, became significantly less than that of control mice with no cell transfer. Furthermore, the significant reduction of the cyst burden by a transfer of the HLA-A2.1-transgenic CD8⁺ immune T cells required an expression of HLA-A2.1 in the recipient NSG mice. Thus, antigen presentation of GRA6Nt by human HLA-A2.1is able to activate anti-cyst CD8⁺ T cells that eliminate T. gondii cysts through antigen presentation by human HLA-A2.1.