HHD transgenic H-2D b-/-b2m -/double knockout mice (6-8 weeks old) purchased from the Institute Pasteur in France were bred and maintained under pathogen-free conditions (Animal & Plant Care Facility, HKUST, Hong Kong, China). HHD mice were originally derived from C57BL mice with the mouse b 2 -microglobulin and MHC I knock-out, and HLA-A*0201 knock-in expressing the chimeric HLA class-I molecules, which were composed of the human b 2 -microglobulin, HLA-A*0201 a-1 and a-2 domains and the a-3 domain of H-2D b [21] .