CD8A and infection: Combining HCT and CD8+ T-cell transfer prevented viral pathogenesis in the recipients (Steffens et al., 1998a), including a CMV-associated graft failure caused by inhibition of bone marrow repopulation due to infection of the bone marrow stroma (Mayer et al., 1997; Steffens et al., 1998b; Renzaho et al., 2020).