IL-2 Stimulated but Not Unstimulated NK Cells Induce Selective Disappearance of Peripheral Blood Cells: Concomitant Results to a Phase I/II Study

In an ongoing clinical phase I/II study, 16 pediatric patients suffering from high risk leukemia/tumors received highly purified donor natural killer (NK) cell immunotherapy (NK-DLI) at day (+3) +40 and +100 post haploidentical stem cell transplantation. However, literature about the influence of NK-DLI on recipient's immune system is scarce. Here we present concomitant results of a noninvasive in vivo monitoring approach of recipient's peripheral blood (PB) cells after transfer of either unstimulated (NK-DLI((unstim))) or IL-2 (1000 U/ml, 9–14 days) activated NK cells (NK-DLI((IL-2 stim))) along with their ex vivo secreted cytokine/chemokines. We performed phenotypical and functional characterizations of the NK-DLIs, detailed flow cytometric analyses of various PB cells and comprehensive cytokine/chemokine arrays before and after NK-DLI. Patients of both groups were comparable with regard to remission status, immune reconstitution, donor chimerism, KIR mismatching, stem cell and NK-DLI dose. Only after NK-DLI((IL-2 stim)) was a rapid, almost complete loss of CD56((bright))CD16((dim/−)) immune regulatory and CD56((dim))CD16((+)) cytotoxic NK cells, monocytes, dendritic cells and eosinophils from PB circulation seen 10 min after infusion, while neutrophils significantly increased. The reduction of NK cells was due to both, a decrease in patients' own CD69((−)) NCR((low))CD62L((+)) NK cells as well as to a diminishing of the transferred cells from the NK-DLI((IL-2 stim)) with the CD56((bright))CD16((+/−))CD69((+))NCR((high))CD62L((−)) phenotype. All cell counts recovered within the next 24 h. Transfer of NK-DLI((IL-2 stim)) translated into significantly increased levels of various cytokines/chemokines (i.e. IFN-γ, IL-6, MIP-1β) in patients' PB. Those remained stable for at least 1 h, presumably leading to endothelial activation, leukocyte adhesion and/or extravasation. In contrast, NK-DLI((unstim)) did not cause any of the observed effects. In conclusion, we assume that the adoptive transfer of NK-DLI((IL-2 stim)) under the influence of ex vivo and in vivo secreted cytokines/chemokines may promote NK cell trafficking and therefore might enhance efficacy of immunotherapy.