On the basis of the success of recent cord blood transplants, we undertook a comparison of the proliferative and cytotoxic potential, following allogeneic stimulation, of E-rosetted T cells from cord blood or adult peripheral blood (PB3) or bone marrow (BM). The magnitude of the proliferative response of cord blood (CB) T cells to alloantigen was greater than or equal to that of adult PB or BM T cells. Proliferation following culture with IL-2, IL-4, or IL-7 produced a similar result. In contrast, the cytotoxic activity in 10 20, or 30 mixed leukocyte culture of CB T cells was minimal, typically less than 20% at an effector:target ratio of 100:1. Cytometric analysis of CB T cell populations before and after culture with allostimulation demonstrated similar ratios of CD4+ and CD8+ cells in cultures of CB and adult T cells. Down-regulation of CD45RA antigen expression, a measure of CD4+ cell activation, was comparable in adult and CB cultures. Activation of CD8+ CTL effectors was assessed by the acquisition of CD28 antigen expression. After culture, a smaller proportion of CD8+CD28+ effector cells was present in CB cultures as compared to adult T cell cultures. Thus, following in vitro priming with alloantigen CB T cells generate a vigorous proliferative response yet produce little antigen-specific cytotoxicity. This diminished cytotoxicity may, in part, be related to the low incidence of graft vs host disease thus far noted in human CB transplants.
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