Poor expansion of adoptively transferred memory T cells in the absence of cognate antigen. (A) MHC class I tetramer identification of CD8⁺ T cells specific for Flu IK9 and Flu GL9 epitopes in the PB of marrow donors and the related recipients (R) at day 90 post–haplo-HSCT. (B) TNF and IFN-γ production by CD4⁺ and CD8⁺ T cells from the haplo-HSCT #10 donor/recipient pair (CMV⁺ and CMV⁻, respectively) following in vitro stimulation with CMV pp65 peptide pool. In panels A and B, numbers indicate the percentage of cells identified by the gates. (C) Summary of the frequency of CD3⁺ natural killer T cells binding CD1d/PBS57 tetramer and Flu and CMV-specific CD4⁺ and CD8⁺ T cells from the PB of donor (D) and the related recipients (R) at day (d) 45 and d90 post–haplo-HSCT. *P < .05, Mann-Whitney test. (D) Differentiation phenotypes of the transferred antigen-specific T cells identified in panel C. Data are presented relative to total memory T cells.