CD8A and infection: As an alternative method to investigate the timing of CD8+-mediated protection, mice received 3 × 106 Pb9-specific cells and i.v. sporozoites, and the immunosuppressive drug FK-506 (tacrolimus), which is reported to block MHC class I Ag presentation (35) but also has T cell immunosuppressive effects, was administered for varying lengths of time during the liver-stage infection period.