Functional CD4⁺ and CD8⁺ T-cell recovery is delayed in CB transplant recipients. We used a cytokine flow cytometric assay wherein peripheral blood mononuclear cells are stimulated with a superantigen (SEB) or an overlapping pentadecapeptide mixture derived from the CMV pp65 protein. We compared SEB-stimulated and CMV-specific CD4⁺ (A) and CD8⁺ (B) T cells at approximately post-CBT day 100 to those seen in other allogeneic PBSC or marrow SCT recipients previously assessed at the same interval using identical methods. In all cases, CB transplant recipients exhibited reduced functional responses measured by the proportion of CD69⁺ IFNγ⁺ T cells after stimulation, relative to allogeneic SC transplantation controls, though differences in CMV-specific T-cell responses were greater in the CD4⁺ subset (vs the CD8⁺ subset). These data demonstrate that a significant subset of CB transplant recipients developed positive CMV-specific T-cell responses from adoptively transferred naive cells by day 100 (CD4⁺: 44% and CD8⁺: 50%). Results are shown only for those patients surviving to day +100, who were assessable (eg, CMV-seropositive), and who had sufficient events in the relevant gate to draw firm conclusions regarding functional frequencies. Error bars represent SEM.