CMV-specific T cells are of recipient origin after R+/D− HSCT but of both recipient and donor origin in the context of R+/D+ HSCT with mixed chimerism. (A) The upper panels illustrate the strategy used for sorting T-cell populations (pregated on CD3). Chimerism patterns are shown for donor and recipient, and subsequently for the selected T-cell populations at 6 months after HSCT. The CD8⁺ compartment is more skewed toward recipient chimerism than the CD4⁺ compartment, and the streptamer⁺ (CMV-specific) CD8⁺ cells show 100% recipient chimerism. (B) In contrast, in the setting of mixed chimerism after R+/D+ transplants, the CMV-reactive CD8+ T cells (streptamer+) come from both donor and recipient compartments, and the recipient chimerism levels were similar in the different cellular compartments (patient 4: CD4⁺ 4%, CD8⁺streptamer⁻ 13%, CD8⁺streptamer⁺ 13%; patient 5: CD4⁺ 80%, CD8⁺streptamer⁻ 86%, CD8⁺streptamer⁺ 85%).