Exploring the immunotherapy potential of natural killer cells

Natural killer (NK) cells are innate immune lymphocytes capable of recognizing and destroying virally infected or malignant cells without prior sensitization. Unlike T cells, which require antigen presentation via MHC molecules, NK cells use a stochastic repertoire of activating and inhibitory receptors to balance signals and determine whether to attack a target. This unique biology makes them an attractive candidate for "off-the-shelf" cancer therapies, as they can be sourced from various donors without the strict HLA-matching requirements that complicate T cell-based treatments.

Research into NK cell-based cancer therapy focuses on two primary pillars: selecting the optimal cell source and enhancing the cells' function within the patient. Current sources under investigation include haploidentical peripheral blood NK cells, umbilical cord blood, stem cell-derived NK cells (including iPSC-derived products), and established NK cell lines. To overcome the immunosuppressive barriers of the tumor microenvironment (TME)—such as hypoxia, TGFβ, and soluble inhibitory ligands—researchers are developing auxiliary strategies. These include the use of pro-inflammatory cytokines like IL-15 to promote survival, and the engineering of chimeric antigen receptor (CAR) NK cells or multi-specific immune cell engagers (such as TriKEs) to redirect NK cells specifically toward tumor antigens.

Tumors employ sophisticated mechanisms to evade NK cell detection, such as downregulating activating ligands or upregulating inhibitory checkpoint receptors. Clinical efforts are now targeting these pathways, including the inhibition of checkpoints like TIGIT, TIM-3, and NKG2A. While early trials with KIR inhibitors showed mixed results, the field is shifting toward combinatorial approaches that pair NK cell infusions with monoclonal antibodies or checkpoint inhibitors to maximize antitumour activity. The goal is to create a robust, persistent, and standardized product that can overcome the hostile TME and provide durable clinical responses.