Expansion of CD56+ NK T and γδ T cells from cord blood of human neonates

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Abstract
A particular T cell population expressing NK cell markers, CD56 and CD57, exists in humans. Many CD56+ T and CD57+ T cells (i.e. NK T cells) exist in the liver and increase in number in the blood with ageing. They may be a human counterpart of extrathymic T cells, similar to NK1.1+ CD3int cells seen in mice. We investigate here the existence of such NK T cells in human cord blood and the in vitro expansion of these cells by the stimulation of human recombinant IL-2 (rIL-2). There were very small populations (< 1.0%) of CD56+ T cells, CD57+ T cells, and γδ T cells in cord blood. However, all of these populations increased in number after birth and with ageing. When lymphocytes in cord blood were cultured with rIL-2 (100 U/ml) for 14 days, CD56+ T cells expanded up to 25% of T cells. CD57+ T cells were never expanded by these in vitro cultures. The expansion of γδ T cells (mainly Vγ9− non-adult type) also occurred in the in vitro culture. A considerable proportion of CD56+ T cells was found to use Vα24 (i.e. equivalent to invariant Vα14 chain used by murine NK T cells) for TCR αβ. These results suggest that neonatal blood contains only a few NK T cells but CD56+ NK T cells and γδ T cells are able to expand in vitro.