Natural killer cell (NK cell) (NK cell)

Natural killer (NK) cells are a distinct lineage of innate lymphoid cells that provide a first line of defense against viral infections and malignancy (Vivier et al., 2008, Science). They are defined phenotypically by the expression of CD56 and the absence of the T-cell receptor complex (CD3) (Caligiuri, 2008, Blood). NK cell activity is governed by a sophisticated balance of activating and inhibitory signals from surface receptors, allowing them to identify and kill cells that have downregulated MHC class I molecules—a phenomenon known as "missing-self" recognition (Ljunggren & Kärre, 1990, Immunology Today). In modern immunotherapy, NK cells are targeted or utilized through various modalities, including cytokine stimulation (e.g., IL-2, IL-15), monoclonal antibodies that block inhibitory checkpoints like NKG2A, and the development of Chimeric Antigen Receptor (CAR)-NK cells (Guillerey et al., 2016, Nature Immunology). Their ability to induce rapid cytolysis via perforin and granzymes, as well as their role in antibody-dependent cellular cytotoxicity (ADCC) via CD16, makes them a central focus for treating hematologic and solid tumors (Smyth et al., 2002, Nature Reviews Cancer). While the term "Natural killer cells not defined)" appears to be a malformed database entry, it refers to this critical population of cytotoxic lymphocytes that are increasingly leveraged in oncology and infectious disease research.

Other names

NK cellsLarge granular lymphocytesCD56+ CD3- lymphocytesInnate lymphoid cells type 1

Modulation of NK cell activity through cytokine-mediated expansion (e.g., IL-2 or IL-15 receptor agonism), checkpoint inhibition of inhibitory receptors such as NKG2A or Killer-cell Immunoglobulin-like Receptors (KIRs), or engagement of activating receptors like CD16 to trigger antibody-dependent cellular cytotoxicity (ADCC) (Guillerey et al., 2016, Nature Immunology; Vivier et al., 2012, Nature).