Ameen, Reem Mohammad; (2001) Phenotypic and functional characterization of cord blood natural killer cells. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Cord Blood (CB) has recently been used as an alternative source of transplantable haemopoietic stem cells with a reported lower incidence of graft versus host disease (GVHD). Lack or reduced GVHD is thought to be associated with higher leukemic relapse as a result of a decrease in the graft versus leukemia (GVL) effect. The GVL effect in cord blood transplantation (CBT) has not yet been fully elucidated. In this study, the phenotypic and functional characteristics of CB natural killer (NK) cells have been investigated since NK cells are recognized effectors in the GVL phenomenon. The expression of CD16, CD56, CD57 NK markers, MHC class I receptors (KIRs and CD94), and CD161 of CB and adult peripheral blood (APB) cell were assessed. A three-color fluorescence cytometric analysis of freshly purified NK cells showed the presence of a unique CD16+/CD56- subset and the absence of CD57+ subset in fresh purified CB NK cells. There was no difference in the expression of KIRs receptors but the expression of CD94 and CD161 was higher in CB than in APB NK cells. When the standard Cr51 release assay was used, CB had a significantly lower cytotoxic activity than APB mononuclear cells (MNCs). However, when the newly developed flow cytometric assay to measure cytotoxicity and purified NK cells was used, there was no significant difference between CB and APB in their ability to induce early apoptotic target cell death. Further studies using K562 and Jurkat cell lines indicated that NK cells from CB and APB use both the Granzyme/Perforin and Fas/FasL cytotoxic pathways. Natural killer cells from CB and APB were incubated with IL-2, IL-12, IL-15, and IL-18 cytokines. The cytokine activated NK (ANK) cells were then assessed for NK markers expression, KIRs, CD94, CD161 receptors and for their NK cytotoxic capacity against K562 and Jurkat cell lines. The results showed that there was a shift towards the CD16+/CD56+ phenotype, in addition to the significant increase in the KIRs receptors in CB ANK cells. No difference in the expression of CD94 and CD161 in CB NK cells was noted. The cytotoxic activity of CB and APB ANK against K562 and Jurkat cells was significantly enhanced. The findings presented in this thesis reveal that CB NK cells have the potential to mediate a GVL effect similar to that observed using APB NK cells.

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