Natural killer cell-based immunotherapies for colorectal cancer: Current strategies, challenges, and future perspectives

Table 1 Regulatory mechanisms of natural killer cell function: Key activating and inhibitory receptors, and molecular interactions

NK cell receptors		Corresponding ligands	Function	Ref.
Activating receptors	CD16 (FcγRIIIa)	Fc segment of IgG	Mediates ADCC through Fc receptor engagement, significantly potentiating tumor cell elimination	[22]
	NKG2D (CD314)	MICA/B. ULBP1-6	Identifies stress-induced ligands on cancerous/infected cells, initiating cytotoxic responses and IFN-γ production	[25,26]
	NKp46 (CD335)	Viral hemagglutinin. Tumor-associated glycoproteins	Mediates targeted cytolysis of virus-infected cells while playing a pivotal role in antitumor immunosurveillance through direct cytotoxic activity	[27,28]
	NKp30 (CD337)	B7-H6. BAT3	Modulates dendritic cell maturation process while potentiating antitumor cytotoxic activity through enhanced immune recognition	[29]
	NKp44 (CD336)	Tumor-associated glycoproteins	Predominantly expressed in activated NK cells, this molecule significantly potentiates the specific cytolytic activity against solid malignancies	[30]
	DNAM-1 (CD226)	CD112 (PVR). CD155 (NECTIN-2)	Forms a corecognition complex with NKG2D to detect MHC-I-deficient cancer cells, initiating perforin-dependent cytolytic pathways for their selective elimination	[31,32]
Inhibitory receptors	KIR family	MHC-I molecules (HLA-A/B/C)	Recognize autologous MHC-I molecules to deliver inhibitory signals that maintain immune tolerance	[33,34]
	NKG2A (CD159a)	HLA-E (binds to MHC-I-derived peptide segments)	Suppresses NK cell activation and preserves self-tolerance through inhibitory receptor signaling	[33,35]
	TIGIT	CD155 (NECTIN-2)	Competes with DNAM-1 for shared ligand binding, thereby attenuating its tumor-suppressive signaling cascade	[31]

NK: Natural killer; IgG: Immunoglobulin G; ADCC: Antibody-dependent cellular cytotoxicity; MICA/B: Major histocompatibility complex class I chain-related proteins A and B; ULBP: UL16-binding protein; IFN-γ: Interferon-gamma; BAT3: Human leukocyte antigen-B-associated transcript 3; PVR: Poliovirus receptor; NKG2D: Natural killer group 2, member D; KIR: Killer cell immunoglobulin like receptor; MHC-I: Major histocompatibility complex class I; HLA: Human leukocyte antigen; TIGIT: Tyrosine-based inhibitory motif domain; DNAM-1: DNAX accessory molecule-1.

Table 2 Antibody-dependent cellular cytotoxicity-inducing therapeutic antibodies in colorectal cancers

Antibody	Mechanism	Ref.
GA201	Anti-EGFR mAb engineered to enhance ADCC, thereby potentiating NK cell-mediated cancer cell lysis	[118]
Cetuximab	EGFR-targeted therapeutic agent that mediates NK cell-dependent ADCC, currently approved as first-line treatment for mCRC	[119,120]
hPR1A3	Demonstrates a 10-fold enhancement in ADCC when evaluated using NK effector cells against CEA-expressing CRC cells	[121]
Trastuzumab	Potentiates NK cell-mediated ADCC in combination with lenalidomide, irrespective of KRAS mutation status or FcγRIIIa polymorphism	[122]
mAb CC4	Enhances NK cell cytotoxic activity against MHC-I-deficient CRC cells	[123]
CO17-1A	NK cell stimulatory factor significantly enhances the cytolytic activity of NK cells against CRC cells	[124]
AFM24	Demonstrates efficacy against EGFR-expressing tumors independent of EGFR expression levels or KRAS/BRAF mutation status	[125]

EGFR: Epidermal growth factor receptor; ADCC: Antibody-dependent cellular cytotoxicity; NK: Natural killer; mCRC: Metastatic colorectal cancer; CEA: Carcinoembryonic antigen; CRC: Colorectal cancer; FcγRIIIa: Fc region receptor IIIa; MHC-I: Major histocompatibility complex class 1.

Table 3 Target antigens for chimeric antigen receptor-natural killer cell therapy in colorectal cancer preclinical studies

Targets	Mechanism	Ref.
EpCAM	CAR-engineered NK-92 cells demonstrate specific recognition and potent cytotoxicity against EpCAM-expressing CRC cells, mediated through targeted release of effector molecules including IFN-γ, perforin and granzyme B	[136]
NKG2D ligands	The CAR construct incorporating NKG2D’s extracellular domain and DAP12 signaling module significantly enhances NK cell-mediated tumoricidal activity	[137]
CD70	CD70 represents an ideal therapeutic target in CRC due to its tumor-restricted expression profile. IL-15-aremed CAR-NK cells demonstrate potent elimination of CD70+ cancerous cells	[99]
CEA	Retrovirally transduced CEA-specific CAR-NK-92MI cells demonstrate significantly enhanced cytotoxic activity (2-3 fold increase) against CEA-expressing tumor models	[138,139]
MSLN	MSLN-directed CAR immunotherapy demonstrates potent efficacy against mesothelin-high CRC models, achieving > 80% tumor volume reduction	[140]
HER2	The HER2-targeted CAR-NK platform represents a novel therapeutic strategy for HER2-amplified CRC, a molecular subset occurring in approximately 5% of cases	[139]
EGFRvIII	EGFRvIII-specific CAR-NK-92 cells demonstrate potent cytotoxic activity against tumor organoids expressing this pan-cancer neoantigen, showing > 90% target cell elimination in preclinical evaluation	[141]
Frizzled receptors	Frizzled receptor-targeted CAR therapies demonstrate specific pro-apoptotic activity against the 15% of CRCs exhibiting Frizzled overexpression	[141]
CD133	CAR133-NK92 cells demonstrate specific cytotoxicity against CD133+ tumor cells through antigen-dependent recognition, while simultaneously synergizing with TLR5 agonist to activate host immune responses against antigen-negative (CD133-) tumor populations	[142]
CDH17	CDH17-CAR-NK cells exhibit potent and selective cytotoxicity against CDH17-high CRC cells. When combined with CD47 blockade, this approach demonstrates synergistic antitumor effects, resulting in enhanced tumor clearance	[143]

EpCAM: Epithelial cell adhesion molecule; CAR: Chimeric antigen receptor; NK: Natural killer; CRC: Colorectal cancer; IFN-γ: Interferon-gamma; NKG2D: Natural killer group 2, member D; DAP12: DNAX-activating protein of 12 kDa; IL: Interleukin; CEA: Carcinoembryonic antigen; MSLN: Mesothelin; HER2: Human epidermal growth factor receptor 2; EGFRvIII: Epidermal growth factor receptor variant III; TLR5: Toll-like receptor 5.