Enhanced Cytotoxic Function of Natural Killer and CD3+CD56+ Cells in Cord Blood after Culture

• CB CD56+ cells can be feasibly expanded ex vivo using IL-2, IL-15, and OKT3.
• CB NK and CD3+CD56+ cells have increased activating receptor expression after culture.
• CB NK and CD3+CD56+ cells have low inhibitory KIR receptor expression after culture.
• NK cells but not CD3+CD56+ cells gain cytotoxic function after culture.

Rate of immune reconstitution directly correlates with the number of hematopoietic stem cells infused and is particularly delayed in patients undergoing cord blood (CB) transplantation (CBT). Methods to increase the number of CB natural killer (NK) cells have the potential to improve immune reconstitution after CBT. NK cells are the first lymphocyte population to recover after hematopoietic stem cells transplantation and are central to preventing early relapse and infection. CB NK cells are low in number and are known to be incomplete in maturation and require activation for effective function. Here, we report a clinically relevant ex vivo expansion method that increases the number of activated CB NK cells. We report a multilog increase in NK cell number when CB mononuclear cells are cocultured with IL-2 and IL-15. Furthermore, NK cells expressing activating receptors and adhesion molecules responsible for cytotoxicity increased throughout culture, whereas inhibitory receptor expression remained low. Additionally, cytotoxic function against various malignancies was significantly enhanced in cultured NK cells but not CD3+CD56+ cells. These data suggest that ex vivo expansion and activation of CB NK cells is a clinically feasible and relevant approach to prevent early infection and relapse after CBT.