Increased number of CD16(+)CD56(dim) NK cells in peripheral blood mononuclear cells after allogeneic cord blood transplantation.

In the present study, we investigated subpopulations of natural killer (NK) cells and the expression of stimulatory and inhibitory NK receptors after adult blood and bone marrow transplantation (BBMT) and cord blood transplantation (CBT). There were significant increases in CD16(+)CD56(dim) cell proportion and in absolute number in peripheral blood mononuclear cells (PBMC) during a period of 4-9 months after CBT compared with these in normal PBMC, cord blood (CB), and in PBMC after BBMT. Also, increased numbers of CD16(+)CD56(dim) NK cells were sustained in some patients until 4 years after CBT. This CD16(+)CD56(dim) cell subset after CBT exhibited decreased expression of NKG2A compared with that in CB and increased expression of NKG2C. Purified CD16(+)CD56(dim) cells from patients 8-9 months after CBT exhibited significantly higher levels of cytolytic activity against K562 than did purified CD16(+)CD56(bright) cells and also whole PBMC. The CD16(+)CD56(dim) cell subset with a high level of cytolytic activity significantly increased after CBT, and these cells may be responsible for NK cell-mediated immunity after CBT.