T-cell responses to rhEPO are HLA-DR or HLA-DQ restricted. (A) T cells from responders were primed and restimulated with heat-stressed HX575, and cultured in the presence (+) of isotype control, anti–HLA-DR, or anti–HLA-DQ antibody. HLA-DR and HLA-DQ restriction of T-cell responses to heat-stressed HX575 is shown in HLA-DRB1*09:01-positive (n = 2) and HLA-DRB1*09:01-negative (n = 3) healthy donors, respectively. (B) HLA-DR restriction of TCL responses to heat-stressed HX575 in HLA-DRB1*09:01-positive donor 8. (C) HLA-DQ restriction of TCL responses to heat-stressed HX575 in HLA-DRB1*09:01-negative donor 2. (D) HLA-DQ restriction of TCL responses to peptide 27 in HLA-DRB1*09:01-negative donor 2. A specific T-cell response shown as SI was calculated by a ratio of cell proliferation with individual stimuli divided by the cell proliferation with vehicle control.