natural killer (NK) cells

Overview

Natural killer (NK) cells are innate lymphoid cells that constitute a critical component of the innate immune system, defined by their capacity to recognize and eliminate infected, stressed, or malignantly transformed cells without requiring prior antigen sensitization. Unlike adaptive immune cells such as cytotoxic T cells, NK cells patrol tissues and circulation armed with germline-encoded activating and inhibitory receptors that enable a rapid, contact-dependent cytotoxic response. Their effector functions include direct target cell lysis through release of cytotoxic granules containing granzymes (GZMA/GZMB) and perforin, engagement of death receptor pathways, and secretion of proinflammatory cytokines such as interferon-gamma (IFNG) and interleukin-6. NK cells also mediate antibody-dependent cellular cytotoxicity (ADCC) through the Fc receptor FCGR3A (CD16), enabling cooperation with therapeutic antibodies to eliminate tumor cells. Their surface microstructures — including microvilli — are essential for target cell recognition and the subsequent formation of immunological synapses, underscoring the importance of membrane architecture in their functional execution.

NK cells occupy a pivotal niche in cancer immunosurveillance through expression of a repertoire of activating receptors, most notably NKG2D, which detects stress-induced ligands upregulated on transformed cells. Their cytotoxic potential can, however, be markedly suppressed within the immunosuppressive tumor microenvironment by factors including transforming growth factor-beta (TGF-β), immunosuppressive steroids such as cortisol, lipid metabolic reprogramming, and inhibitory glycoimmune checkpoints such as Siglec-7 and Siglec-9. The dynamic interplay between activating and inhibitory signals — including those mediated by checkpoint receptors like NKG2A, TIGIT, and CLEC12B — determines the net cytotoxic output of NK cells in both physiological and pathological settings. Ongoing research is rapidly expanding both the mechanistic understanding and therapeutic exploitation of NK cell biology across a wide range of malignancies.

Focus of Latest Publications

Recent publications have positioned NK cells at the center of a broad and rapidly evolving cancer immunotherapy landscape, with investigations spanning their fundamental biology, suppression mechanisms, engineering strategies, and combinatorial therapeutic potential.

Checkpoint and glycoimmune regulation. Several studies have examined how inhibitory receptor signaling constrains NK cell anti-tumor activity. Work published in Oncoimmunology (PMID 41928453) investigated the role of sialic acid cis-ligand dynamics in modulating Siglec-7 and Siglec-9 function on NK cells. These glycoimmune checkpoints, expressed on primary NK cells isolated from peripheral blood, interact with sialylated ligands presented in trans on tumor cells but also in cis on the NK cell surface itself. The study demonstrated that Siglec-7 and/or -9 blockade increased NK cell-mediated killing of melanoma and acute myeloid leukemia (AML) cell lines, as well as patient-derived AML cells, establishing co-blockade of both receptors as a strategy to potentiate anti-tumor activity. Complementary findings in Cancer Immunology, immunotherapy (PMID 41961075) showed that targeting ST3GAL1 to downregulate sialylated ligands for Siglec-7 in hepatocellular carcinoma could reverse immune escape. Additionally, a study in Nature Communications (PMID 41998001) on ovarian carcinoma found that NKG2A inhibition not only enhanced NK cell cytotoxicity but also promoted productive NK cell–CD8+ T cell interactions, underscoring the crosstalk between innate and adaptive effectors in anti-cancer immunity. In Nature Immunology (PMID 41844941), CLEC12B was identified as an inhibitory receptor on NK cells that, when targeted, enhanced cancer immunotherapy efficacy within the immunosuppressive tumor microenvironment.

Checkpoint editing and genetic reprogramming. Building on checkpoint biology, a study in Cancer Research (PMID 41982126) employed base-editing technology to disrupt TIGIT in NK cells, reprogramming CD155 signaling to enhance anti-tumor efficacy. Separately, work in The Journal of Experimental Medicine (PMID 42126429) demonstrated that nonviral precision genome editing of NK cells using homology-directed repair (HDR) could reprogram endogenous NK circuits, addressing longstanding challenges of poor HDR efficiency and DNA toxicity that limited prior off-the-shelf immunotherapy manufacturing. The SMAD7-mediated resistance to TGF-β suppression was described in Journal for immunotherapy of Cancer (PMID 41956539), where SMAD7 overexpression in NK cells was shown to enhance antitumor activity through canonical TGF-β blockade and non-canonical transcriptional activation of STAT5A, the latter representing a newly characterized mechanism for preserving NK cell function in the tumor microenvironment.

CAR-NK engineering and off-the-shelf therapy. The field of chimeric antigen receptor (CAR)-NK cell therapy was reviewed comprehensively in Immunology and Cell Biology (PMID 42003566), highlighting translational and regulatory breakthroughs in CAR-NK platforms as alternatives to CAR T cell therapies. CAR-NK cells were specifically studied in the context of cortisol-mediated immunosuppression in Signal Transduction and Targeted Therapy (PMID 41956993), where cortisol-resistant CAR-NK cells were engineered to overcome steroid-induced suppression in lung cancer, a mechanism that had been underexplored relative to other immunosuppressive factors. The NKG2D receptor, described as a central component of immune surveillance expressed on NK cells and several T lymphocyte subsets, was also targeted in the context of engineered T-cell strategies to treat human disease (Human Vaccines & Immunotherapeutics, PMID 41656162).

Adoptive transfer, ADCC, and allogeneic transplantation contexts. A study in Oncoimmunology (PMID 42216567) demonstrated that umbilical cord blood-derived NK cells improve the efficacy of anti-GD2 antibody in neuroblastoma by amplifying ADCC, translating findings from mouse models to human cells and highlighting the role of FCGR3A-mediated mechanisms. In the context of allogeneic haematopoietic stem cell transplantation (allo-HSCT) for AML, a review in Annals of Medicine (PMID 41622937) synthesized emerging evidence on the synergistic roles of T cells and NK cells in transplant immunity, noting the importance of NK cell reconstitution. A complementary clinical study in Cancer Letters (PMID 41720450) assessed the prognostic significance of HLA-B leader matching status and its relationship with NK cell reconstitution in patients with hematological malignancies following haploidentical hematopoietic stem cell transplantation.

Memory-like and trained NK cells. Two studies highlighted NK cell plasticity beyond their classical innate role. In Blood Advances (PMID 41538301), exercise-mobilized lymphocytes were shown to enhance the function of cytokine-induced memory-like (CIML) NK cells — generated by short-term activation with IL-12, IL-15, and IL-18 — against myeloid leukemia following adoptive transfer. In Molecular Therapy (PMID 42237539), a single dose of therapeutic Salmonella was found to confer long-lasting protection against cancer metastasis in mice by inducing "trained" NK cells, a form of innate immune memory that persisted to provide durable anti-metastatic surveillance.

tumor microenvironment modulation and combination strategies. Numerous studies examined how manipulating the tumor microenvironment (TME) influences NK cell infiltration and function. A study in Biomaterials (PMID 41587524) showed that spatiotemporal control of neutrophil extracellular traps increased infiltration of NK cells and T cells, while promoting anti-tumor polarization of neutrophils and macrophages to reverse the immunosuppressive TME. In ACS Nano (PMID 41949057), engineered BCG was shown to recruit M1-type macrophages, NK cells, and induce dendritic cell maturation at the tumor site in triple-negative breast cancer. A neoantigen and shared MICB α3 antigen dual-targeted vaccine (EMBO Molecular Medicine, PMID 41998137) improved NK cell and neoantigen-specific T cell infiltration across multiple preclinical models. Lipid metabolism reprogramming within the TME was identified in Cellular & Molecular Immunology (PMID 41946907) as a driver of NK cell and CD8+ T cell dysfunction, linking metabolic perturbations to immune suppression. Engineered NK and T cells equipped with metabolite-sensing receptors were reported in Nature Immunology (PMID 41872506) to improve tumor infiltration and eradication in solid tumors. In Journal of Controlled Release (PMID 41905408), targeted lipid nanoparticle co-delivery of decitabine and siTNF-α to the bone marrow niche enhanced CD8+ T, NK, and NKT cell infiltration in leukemia therapy.

NK cell subsets and clinical biomarkers. A phase II clinical trial combining pembrolizumab with paclitaxel and carboplatin in melanoma (Oncoimmunology, PMID 41732954) found that objective response was associated with a larger proportion of mature NK cells at baseline, alongside lower frequencies of naive CD8 T cells and low plasma CCL3, situating NK cell maturation status as a predictive biomarker. In nasopharyngeal carcinoma, British Journal of Cancer (PMID 41992060) characterized alterations in NK cell subsets in patient blood and examined the regulatory role of JAB1 in tumor immunity. Evasion of NK cell-mediated killing was systematically reviewed in Pharmaceutical Science Advances (PMID 41799416), cataloging mechanisms by which tumor cells evade the innate cytotoxic response and surveying advances in NK cell-based cancer immunotherapy.