HHV8-specific CD8 T cells in a seronegative transplant recipient exposed to the virus through the graft. The figure shows the staining of the tetramer⁺ population for the indicated peptides (A), their perforin expression (B), and their phenotype profile (C), performed 12 months after transplantation with a kidney graft from an HHV8-infected donor. (A) Boxes delineate the tetramer⁺ CD8 T-cell population.