A recent study reported that quantitation of cytomegalovirus (CMV)-specific CD8ΓΎ T lymphocytes in the graft and monitoring of these T cells might identify hematopoietic stem cell transplantation-recipients at the risk for progressive CMV infection. A 6-year-old girl underwent bone marrow transplantation from an HLA-identical sibling with a very high frequency of CMV specific tetramer-positive CD8ΓΎ T-cells. CMV-specific T-cell immunity was prospectively evaluated using a peptide (HLA-A2, NLVPMVATV). Tetramer assay showed that the frequency of CMVspecific CD8ΓΎ T cells of the donor in the peripheral blood was 5.3%, higher than average amongst young children. The frequency of CMVspecific CD8ΓΎ T cells of the donor in the graft was 3.7% of CD8ΓΎ T-cells. Before transplantation, the frequency of CMV specific CD8ΓΎ T cells of the recipient was 0.1% in the peripheral blood. Surprisingly, the frequency of CMV specific CD8ΓΎ T cells increased up to 30% of CD8ΓΎ T-cells at day 27 after transplantation. IFN-g enzymelinked immunospot assay showed the recipient-T cells had strong responses to the A2-specific NLVPMVATV peptide. Although the phenotypic pattern of the CMV-specific T cells of the recipient was different from those of the donor before transplantation, the phenotype of the donorderived cells retained their original phenotype in the recipient after transplantation. These finding suggested that active transferred immunity from the graft with a high frequency of CMVspecific CTL could induce a rapid reconstitution of CMV-specific T-cell mediated immunity in pediatric HLA-identical allogenetic bone marrow transplantation. The screening of peripheral blood using HLA-peptide tetramer staining might be beneficial to select donors.