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6 General discussion and Future Prospects | 145 is coming mainly from industry. Although NK cells can be effective in some types of cancer as a monotherapy, considering their heterogeneity, complex networking and the inherent adaptability of several tumors to evade killing by immune cells, it is likely necessary to improve on the efficacy of currently availableNK cell products. In this respect, it isworthwhile to consider combinatorial approaches of different treatment strategies involving NK cells. A summary of biotech companies involved in NK cell research is listed in Table 1 and Figure 1. Here, we review for a selected group of NK cell companies, which develop NK cell specific treatments, the underlying scientific principles and findings of their product pipelines, revealing highly innovative concepts that herald future clinical applications. Cytokines to enhance NK cell functions To improve the anti-tumor activity of autologous NK cells, systemic administration of clinical grade recombinant IL-2 (rIL-2) and single chain IL-15 (scIL-15) have been used in high doses and this has resulted in severe grade 3/4 toxicities 8-10 . Since then their safety and efficacy have been tested in low doses following NK cell adoptive transfer in cancer patients 11-13 . However, IL-2 resulted in expansion and mobilization of inhibitory T-regs, severely limiting Figure 1: Summary of NK cell biotech companies and landmark clinical trials from academia and biotech industries.