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Ex Vivo Expansion and Activation of Natural Killer Cells from Thalassemia Patients for Adoptive Immunotherapy of Tumors

Therapeutic outcomes for high grade soft tissue and bone sarcomas still remains poor, which is largely due to severe chemoresistance of this aggressive tumor type. Therefore, alternative approaches are needed addressing novel targets that are different from current multimodal chemotherapy. Natural killer cells are a major component of the innate immune system due to their ability to exert direct cytotoxicity against malignant cells or otherwise stressed cells. Interest in natural killer cell-based immunotherapy has increased since new protocols for the purification and expansion of large numbers of highly cytotoxic cells have become available. Peripheral blood mononuclear cells from patients with different thalassemia subtypes were co-cultured with irradiated, genetically engineered K562-mb15-41BBL cells in the presence of interleukin-2 for 14 d. Expansion efficiency, natural killer cell receptor repertoire and the expression of natural killer cell ligands on cell lines were investigated by flow cytometry. Cytolytic activity of natural killer cells was tested using the europium target detection assay based on time-resolved fluorometry. Ex vivo expansion of peripheral blood mononuclear cells from thalassemia patients allowed the generation of large numbers of natural killer cells exhibiting enhanced activation characteristics and high cytolytic activity against tumor-cell lines, yet retaining tolerance towards normal body cells. Moreover, this method has been adapted to clinical-grade conditions, producing a sufficient quantity of highly cytotoxic natural killer cells for immunotherapy. Based on these data, adoptive transfer of ex vivo expanded and activated natural killer cells deserve further clinical evaluation as a possible new treatment option for tumor and other blood diseases patients.