Cytokines secreted by alloreactive donor T cells play a crucial role in the pathogenesis of both acute and chronic GvHD, a complication of allogeneic hematopoietic transplants that occurs at a lower incidence and severity when human umbilical cord blood (HUCB) is used. Our five-dimensional flow cytometric study performed on 20 HUCB and 20 peripheral blood (PB) samples from healthy adults was focused on the Th1/Th2 cytokine profile of activated HUCB T cells. Lymphocytes of all samples were stimulated by specific mitogens, and cytokine secretion was blocked at the cytoplasmic level. CD4+ and CD8+ cells were then analyzed for surface expression of the very early human activation antigen CD69 and for IFN-γ and IL-4 intracellular production as expression of Th1-like and Th2-like T cell cytokine response, respectively. HUCB T lymphocytes were shown to be unable to perform both a Th1-like and Th2-like response, as compared with normal PB T cells. However, all lymphocytes from both sources were normally activated, as indicated by regular expression of the CD69 molecule. These data suggest that the low response of HUCB T lymphocytes to mitogens may be responsible for the decreased incidence of acute and chronic GvHD and provide possible explanations for the clinical results in HUCB transplantation.
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