Ex vivo expansion of CD56+ cytotoxic cells from human umbilical cord blood

Objective. The immune-mediated effect of natural killer (NK) and cytotoxic T cells against residual tumor cells previously was shown to prevent relapse and reinduce remission after bone marrow transplantation. Human umbilical cord blood is a rich source of cytotoxic CD56(+) cells including fetal NK cells (CD16(-)CD56(++)) with high IS tic capabilities upon activation with interleukin-2 (IL-2), Cord blood transplantations are reported to be associated with lower risk of graft-vs-host disease, which may jeopardize the graft-vs-leukemia effect. Therefore, our goal was to expand and amplify, ex vivo, cord blood-derived CD56(+) cell-mediated cytotoxic activity, Materials and Methods. Cord blood-derived CD56(+) cells were separated using anti-CD56 monoclonal antibody and immunomagnetic beads. The tells were expanded in the presence of irradiated feeder cells and various concentrations of IL-2. Results. Maximal fold expansion (152 +/- 29) was achieved on day 22 by culturing the cells in the presence of irradiated autologous lymphocytes. Irradiated murine stromal cells yielded 42 +/- fourfold expansion (p < 0.05), FACS analysis at the peak of expansion revealed that the cells were 96% +/- 1% CD56(+), Interferon-<gamma> levels significantly decreased throughout the culture period (from 1,034 +/- 34 pg/mL to 21 +/- 8 pg/mL) as did IL-6 levels (from 11,535 +/- 1,452 pg/mL, to 323 +/- 161 pg/mL) whereas tumor necrosis factor-alpha levels did not change. The expanded cells manifested potent lytic capabilities against K562 and Colo-205 cell lines (70.9% +/- 2.0% and 48.2% +/- 4.0%, respectively) (n = 5) (effector-to-target ratio 25:1), Coculturing the expanded NK cells with fresh ALL blasts resulted in 85% +/- 1% inhibition of colony growth in methylcellulose (n = 2), In addition, the CD56(+) expanded cells induced 44% +/- 7.5% apoptosis of K562 target cells (n = 3). Conclusions. It is possible to effectively expand cord blood-derived CD56(+) cells, ex vivo, while maintaining their antileukemic capablilities. (C) 2001 International Society for Experimental Hematology. Published by Elsevier Science Inc.