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This study was purposed to comparatively analyze the early T-lymphocyte subsets and T-cell receptor excision cycles (TREC) reconstruction in recipients with hematologic malignancies after myeloablative unrelated cord blood transplantation (UCBT) and sibling donor bone marrow and/or peripheral blood stem cell transplantation (BMT/PBSCT). The peripheral blood T lymphocyte subsets were detected using flow cytometry and TREC were detected using real-time quantitative PCR for 40 patients with hematologic malignancies in the first six months after myeloablative allogenic hematopoietic stem cell transplantation. The results showed that in the first month after transplantation, the absolute counts of CD3(+), CD3(+) CD4(+), CD3(+) CD8(+) cells were lower significantly in the UCBT group than those in the BMT/PBSCT group. And later the absolute counts of CD3(+), CD3(+)CD4(+), CD3(+)CD8(+) cells were not different between two groups. The ratio of CD3(+)T subset in the peripheral blood lymphocytes of the UCBT recipients was lower, but the difference was not statistically significant within 2 months after transplantation. The ratio of CD3(+)CD4(+) cells in the patients received the UCBT and BMT/PBSCT decreased obviously since engraftment happened. The CD3(+)CD4(+) cells on the 2 months after transplantation fell to the lowest level, then gradually increased, but did not reach to the normal level until 6 months after transplantation. CD3(+)CD8(+)cells were well reconstituted, rising to normal at the engraftment after transplantation, with a low CD4(+): [KG-*2] CD8(+) ratio over the first 6 months after transplantation. Compared with the BMT/ PBSCT group, the naive T cells (CD3(+)CD4(+)CD45RA(+)CD62L(+)) were more in the first month after transplantation and the terminally differentiated effector memory T cells (CD3(+)CD4(+)CD45RA(+)CD62L(-)) were more at the 3 month after transplantation in the UCBT group, and those were significantly more than the normal control group. TREC were lower and did not recovered until 6 months after transplantation in the recipients of the two groups. It is concluded that compared with sibling donor's BMT/PBSCT, early T cell reconstitution significantly delayed after UCBT, but the terminally differentiated effector memory T cells are higher after transplantation, and thus play a anti-infective or anti-leukemia role.