EXPANSION OF CD56(-T-CELLS AND GAMMA-DELTA-T-CELLS FROM CORD-BLOOD OFHUMAN NEONATES() NK)

A particular T cell population expressing NK cell markers, CD56 and CD 57, exists in humans. Many CD56(+) T and CD57(+) T cells (i.e, NK T ce lls) exist in the Liver and increase in number in the blood with agein g. They may be a human counterpart of extrathymic T cells, similar to NK1.1(+) CD3(int) cells seen in mice. We investigate here the existenc e of such NK T cells in human cord blood and the iii vitro expansion o f these cells by the stimulation of human recombinant IL-2 (rIL-2). Th ere were very small populations (< 1.0%) of CD56(+) T cells, CD57(+) T cells, and ya T cells in cord blood. However, all of these population s 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 expan ded by these in vitro cultures. The expansion of gamma delta T cells ( mainly V gamma 9(-) non-adult type) also occurred in the in vitro cult ure. A considerable proportion of CD56+ T cells was found to use V alp ha 24 (i.e. equivalent to invariant V alpha 14 chain used by murine NK T cells) for TCR alpha beta. These results suggest that neonatal bloo d contains only a few NK T cells but CD56(+) NK T cells and gamma delt a T cells are able to expand in vitro.