Advancing CAR-NK cell therapy in solid tumors: Current landscape and future directions.

Introduction

Chimeric antigen receptor (CAR)-T cell therapy has revolutionized the management of hematologic malignancies, providing durable responses even in patients with relapsed or refractory disease. 1 However, considerable barriers remain to broader adoption, particularly against solid tumors. 2 Significant challenges include life-threatening toxicities such as cytokine release syndrome (CRS) and neurotoxicity, the requirement for autologous manufacturing, lengthy collection-to-infusion intervals, and substantial costs, limiting accessibility and feasibility. 3

In contrast, natural killer (NK) cells provide unique advantages for cancer immunotherapy. 3 They are capable of directly eliminating malignant or virally infected cells without prior sensitization. 4 NK cells detect and kill major histocompatibility complex (MHC) class I negative cells by recognizing the absence of inhibitory signals and engaging activating receptors, triggering apoptosis of target cells. NK cells contribute to immunosurveillance via both direct cytolytic activity and antibody-dependent cellular cytotoxicity (ADCC). Their innate capacity for immediate anti-tumor action, potential for allogeneic use without graft-versus-host disease (GvHD), and lower propensity for cytokine storms make NK cells an attractive cell therapy platform. 3

As a modern cell-based immunotherapy, CAR-NK cells address many shortcomings of CAR-T cell therapy. 3 Introducing CARs into NK cells enables harnessing both innate and engineered anti-tumor capacities of NK cells within an “off-the-shelf” therapeutic product. 3 Early clinical investigations, including our group’s first-in-human phase I/II trial using cord-blood-derived, CD19-targeting CAR-NK cells in relapsed/refractory hematological malignancies, demonstrated robust anti-tumor efficacy with a favorable safety profile. 5 , 6

Despite their promise, CAR-engineered cell therapies in solid tumors are constrained by a hostile tumor microenvironment (TME) characterized by hypoxia, nutrient deprivation, acidification, physical barriers, and a diverse array of immunosuppressive cells and molecules, all of which conspire to impair immune cell infiltration, persistence, and function. 3 NK cells are additionally mired by limited persistence and challenges in trafficking and infiltration into tumors. These obstacles underscore the need for engineered cell therapies that are both intrinsically resilient to TME-mediated suppression and readily accessible for broader patient use. Here, we detail CAR-NK cell manufacturing. We then review the multifaceted challenges posed by both the TME and NK cell biological underpinnings. We outline rational preclinical advancements and emerging strategies to overcome immunometabolic and physical barriers, rendering more potent and effective CAR-NK cell therapies for solid tumors. Finally, we discuss the current clinical landscape of CAR-NK cell therapy for solid tumors as a nascent, evolving space with promising potential.

Cell sources for CAR-NK cell generation

CAR-NK cells can be generated from various sources, including peripheral blood (PB), umbilical cord blood, pluripotent stem cells, and NK cell lines (graphical abstract).

Peripheral blood

PB is an easily accessible source of CAR-NK cells. Autologous PB-NK cells circumvent immune rejection, while allogeneic NK cells from healthy donors can treat multiple patients from a single donor. Autologous NK cells from patients can be less effective because of self-MHC-based inhibition or impaired by disease conditions or previous treatments. 7 Therefore, allogeneic PB-NK cells are preferred for NK cell therapy. Allogeneic NK cells are mature and require a short differentiation process. However, NK cell frequency in PB is low, 8 necessitating expansion to generate a therapeutic scale, representing a major drawback. Other challenges with PB-NK cells include donor-dependent variability, exhaustion due to prolonged activation, and relatively low transduction efficiency. 9 To optimize NK cell expansion and functionality, several cytokine cocktails have been tested, along with feeder cells and metabolic components. 10 , 11 , 12

Umbilical cord blood

Umbilical cord blood (CB) is a highly proliferative source of CAR-NK cells. 13 A single cord can generate “off-the-shelf” CAR-NK cells at a clinical scale to treat multiple patients with robust functionality and long-term persistence. 14 , 15 We published the first phase I/II clinical trial using CB-derived CAR-NK cells targeting CD19 against relapsed/refractory hematological malignancies, showing an excellent safety profile with a robust therapeutic efficacy, indicating the promise of CB-derived CAR-NK cells. 6

Similar to allogeneic peripheral blood mononuclear cells (PBMCs), donor-to-donor variability presents a limitation. Correlative data from the aforementioned trial identified key characteristics of optimal CB units for CAR-NK cell therapy. We identified that CAR-NK cells derived from CB units with ≤8 × 10 7 nucleated red blood cells (RBCs) and a collection-to-cryopreservation time of ≤24 h strongly predicted better clinical outcomes. CAR-NK cells derived from these units demonstrated superior anti-tumor efficacy in murine models and enrichment of effector-related genes. 6 Suboptimal CB units yielded NK cells with upregulation of inflammation, hypoxia, and cellular stress programs. These findings reveal new aspects of CAR-NK cell biology and highlight the importance of donor selection for allogeneic cell therapies.

Pluripotent stem cells

Embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) are another source of CAR-NK cells. Stem cells are genetically modified at the pluripotent stage to express the CAR construct due to easier gene editing and clonal selection, followed by staged differentiation into NK cells. 16 Advantages include unlimited expansion potential and reduced donor-dependent variability, rendering an ideal source for “off-the-shelf” CAR-NK cells with unmatched genetic programmability. However, the process is time-consuming and relatively inefficient. Moreover, NK cells differentiated from iPSCs can show an immature phenotype with low KIR and CD16 expression, limitations that could be partly overcome with genetic engineering to maintain cytotoxic capacity. 17 Additionally, the introduction of genetic abnormalities during reprogramming may cause malignant transformation. 18 Despite challenges, recent advances in more efficient protocols for NK cell generation showcase enormous potential for stem cells as a CAR-NK cell platform. 19

NK cell lines

NK-92 is an NK cell line derived from the PB of a 50-year-old male with non-Hodgkin lymphoma in 1992. NK-92 is easy to expand on a therapeutic scale with low variability and straightforward to genetically manipulate for CAR-NK engineering. However, NK-92 requires pre-infusion irradiation to prevent uncontrolled proliferation in vivo and potential tumorigenicity. Although clinical trials with NK-92 were safe and showed promising short-term efficacy, their limited persistence hinders sustained long-term effectiveness, requiring repeated treatments. 20 , 21

Considerations for NK cell expansion and cryopreservation

NK cell expansion

Since NK cell frequency is low and large numbers are needed for cell therapy, expansion is necessary. Different expansion methods include cytokines, feeder cells such as K562 cells expressing membrane-bound cytokines, and feeder-free particle-based methods. 15

Expansion conditions materially shape NK cell biology, wherein feeder-based protocols maximize proliferation up to 2,400-fold and produce NK cells with high cytotoxic potential. 22 Cytokine-only approaches (e.g., with interleukin (IL)-2 23 or IL-15 23 ) are less labor-intensive with good short-term cytotoxicity but yield lower expansion of <10- to 20-fold, with a higher subset of immature CD56 bright NK cells. 24 Certain cytokine cocktails may induce a memory-like phenotype. 25 , 26

Aside from expansion, further obstacles include optimizing the efficiency of transduction or gene editing and maintaining NK cell viability and proliferative capacity. 27 , 28 K562-based cell lines are the most common feeder cells for ex vivo NK cell expansion. K562 is a tumor cell line derived from a patient with blast crisis of chronic myelogenous leukemia (CML), therefore requiring irradiation before use. Residual K562 may be left in the final product, necessitating strict requirements from the Food and Drug Administration (FDA) to ensure no residual feeder cells are present in final clinical-grade NK cell products. 29 Thus, alternative NK cell expansion methods, such as artificial antigen-presenting cells or feeder-free particle-based expansion methods, are being explored to improve safety and follow regulatory standards for clinical application. 27

Challenges of NK cell cryopreservation

Cryopreservation of NK cells is essential for scalability, enabling off-the-shelf availability and broad clinical deployment. Unlike T cells, which maintain cytotoxicity after freeze-thaw cycles, the post-thaw viability and recovery of NK cells are significantly affected. This compromises their ability to expand, persist, and kill tumor cells in vivo . 30

Several factors contribute to these differences between NK cells and T cells. Compared to T cells, NK cells have more pre-formed cytotoxic granules. 31 Moreover, NK cells have activating receptors that recognize stress ligands on damaged cells. 32 These unique characteristics of NK cells lead to increased apoptosis post-thaw, likely due to cryoinjury resulting in intracellular leakage of granzyme B (GZMB) from pre-formed cytotoxic granules or fratricide following the induction of cellular stress recognized by neighboring NK cells. A recent report showed that cryopreserved NK cells undergo apoptosis post-thaw due to GZMB leakage from cytotoxic granules. 33

Optimizing cryopreservation strategies is essential for effective off-the-shelf NK cell therapies. IL-15 and IL-18 pre-treatment improves NK cell tolerance to cryopreservation by inducing anti-apoptotic genes and transient reduction in intracellular GZMB levels. 33 Resting thawed NK cells overnight in IL-2 or IL-15 yields NK cells with improved cytotoxicity. 34 DMSO impairs NK cell cytotoxicity by inducing a functionally compromised CD56 dim CD16 − NK cell subset 35 and reduces the NK-cell-activating pathways TRAIL and NKG2D. 36 DMSO-free cryoprotective options include trehalose-loaded nanoparticles or dextran/CPLL combinations. 37

Among cell sources, NK-92 cells have the highest post-thaw viability. 38 PB-derived NK cells show reduced post-thaw viability with a mean of 34% after 24 h, dependent on donor and cryopreservation length. 11 , 23 CB-derived NK cells experience good recovery after cryopreservation. 39 Some reports described poor recovery of iPSC-derived NK cells, recommending that thawed products are expanded before infusion. 40 Others described excellent post-thaw recovery and function of iPSC-derived NK cells. 41 , 42

Advantages of CAR-NK cells for the treatment of solid tumors

CAR-NK cells offer advantages over CAR-T cells, including safety and cost-effective manufacturing as allogeneic “off-the-shelf’ therapies.

Allogeneic potential, scalability, and reduced cost

GvHD is a major limitation to off-the-shelf allogeneic CAR-T cell therapies, even in HLA-matched settings, thereby reinforcing the reliance on autologous manufacturing strategies or genetic modifications. 43 To reduce GvHD risk, allogeneic, “off-the-shelf” iPSC or CB-derived CAR-T cells involve TRAC knockout, disrupting the native T cell receptor (TCR). 44 , 45 However, this may reduce CAR-T cell quality and their innate functionality. 45 In contrast, NK cells do not cause GvHD even with HLA mismatching, 46 enabling the use of allogeneic off-the-shelf CAR-NK cells derived from healthy donors or cell lines. 47 This eliminates the need for time-intensive and costly patient-specific manufacturing, reducing time to treatment. 48

Dual innate and engineered anti-tumor activity

NK cells express a diverse array of activating receptors that enable the selective recognition and elimination of malignant cells through both direct cytotoxicity and ADCC. Consequently, CAR-NK cells can engage cancer cells by both engineered CARs and innate, germline-encoded receptors. This dual recognition capacity may reduce the risk of antigen escape with tumor heterogeneity. 49

Safety profile

CAR-T cell therapy is associated with significant toxicities, including CRS and immune-effector-cell-associated neurotoxicity syndrome (ICANS), driven by the massive release of proinflammatory cytokines initiating a cascade of immune responses. This “cytokine storm” can lead to fever, hypotension, hypoxia, and multi-organ dysfunction. Severe CRS (≥grade 3) occurs in up to 30% of patients, depending on the CAR construct and disease context. 50 , 51 ICANS affects up to 50% of patients following CAR-T therapy. 51 Emerging reports describe non-classical neurotoxicity symptoms, such as parkinsonism and movement disorders, following CAR-T cell therapy for multiple myeloma, suggesting potential off-tumor effects on basal ganglia or neuroinflammatory mechanisms beyond typical ICANS. 52

In contrast, early clinical data suggest that CAR-NK cells have a more favorable safety profile. Generally, severe CRS (≥grade 3) has not been observed, and neurotoxicity has not been reported in early trials. 6 Reported adverse effects have been mostly manageable including transient cytopenias and mild infusion reactions or ≤grade 2 CRS. 5 , 21 , 53

Immunomodulation by NK cells

Although classically defined by direct cytotoxicity, accumulating evidence suggests that NK cells natively function as rheostats of immunity. 54 The most well-known is through the secretion of cytokines or chemokines, including TNF-α, CCL5, interferon gamma (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF), which render an immune-permissive TME by recruiting dendritic cells (DCs) and effector T cells. 55 Additionally, these factors enhance endothelial adhesion molecule expression and may form chemokine gradients to draw in lymphocytes. 56 IFN-γ production is a hallmark feature of NK cells and boosts immune responses by T H 1 polarization of CD4 + T cells, 57 suppressing MDSCs, 58 enhancing macrophage M1 polarization, 59 and upregulating MHC-class I as well as antigen-processing machinery on tumor cells. 60 NK cells also directly engage with DCs, promoting their maturation and production of IL-12 and eliminating tolerogenic DCs, indirectly shaping adaptive immunity. 61 In turn, DCs also enhance NK cell activation. 62 Additionally, if armored with IL-15, NK-cell-elaborated IL-15 contributes to immunomodulation. 63

Limitations of CAR-NK cell therapy in solid tumor therapeutics

Despite the relative success of CAR-NK immunotherapies in hematologic malignancies, 5 significant challenges remain in the context of solid tumors, including enhancing NK cell expansion, persistence, optimal antigen recognition, homing, and infiltration while preventing exhaustion within the immunosuppressive TME ( Figure 1 ). 64

Poor persistence

Unmodified NK cells naturally have a short lifespan of approximately 2 weeks and limited capacity for long-term survival and proliferation post-infusion without cytokine support. 64 This limitation is compounded within the hostile TME, where physical and biochemical barriers such as hypoxia, nutrient deprivation, and immunosuppressive molecules promote NK cell apoptosis and contribute to limited persistence ( Figure 1 ). Chronic activation from persistent exposure to tumor cells can also lead to NK cell exhaustion and activation-induced cell death. Fortunately, research demonstrates that cytokine armoring with IL-15 64 and IL-21 65 enhance NK cell persistence and long-term function.

Suboptimal trafficking

A principal barrier in solid tumors is the inadequate trafficking of immune cells to tumors. NK cell trafficking to tumors involves a coordinated series of events, including rolling and adhesion to endothelial cells mediated by selectins and integrins and directional migration along chemokine gradients. 66 , 67 Compounding the poor access due to abnormal tumor vasculature and dense extracellular matrices (ECMs), solid tumors often lack normal expression of adhesion molecules and selectins that are required for effective trafficking. 68 Mismatched chemokine-receptor profiles between tumor-secreted chemokines and CAR-NK cell receptors restrict entry. 69 To surmount NK cell homing obstacles, local delivery strategies are being applied in both preclinical studies and clinical trials, such as intracranial, intraperitoneal, intrapleural, or intratumoral injection. 70 , 71 , 72 , 73

Insufficient infiltration and physical barriers

Unique to solid tumors is their ability to restructure the TME to evade immune surveillance and infiltration by secreting factors that recruit stromal cells and fibroblasts ( Figure 1 ). 74 Cancer-associated fibroblasts (CAFs) secrete factors such as transforming growth factor β (TGF-β), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), lysyl oxidases, and matrix metalloproteinases (MMPs), remodeling the ECM to promote dense, cross-linked, and disorganized collagen deposition, increasing stiffness and interstitial fluid pressure within the TME.

Aberrant vasculature

A key component of the immunosuppressive TME is the presence of aberrant and leaky vasculature ( Figure 1 ). With tumor growth, cancer cells and CAFs secrete pro-angiogenic factors such as VEGF, fibroblast growth factor (FGF), and PDGF, promoting blood vessel formation to support nutritional demand. The tumor and CAFs also produce MMPs and TGF-β that degrade and remodel the ECM resulting in disorganized, immature vasculature with heightened vessel permeability. 75 Under normal conditions in vivo , NK cells circulate through the vasculature and are guided to sites of stress by chemokines, allowing migration across the blood vessel endothelium to an affected area. Utilizing integrins, NK cells anchor to ICAM-1 and VCAM-1 on the surface of the vasculature endothelium to facilitate this migration. 76 In the TME, pro-angiogenic factors such as VEGF downregulate ICAM-1 and VCAM-1 on the vessel endothelium, antagonizing NK cell migration to tumor sites. Additionally, leaky vasculature leads to the accumulation of interstitial fluid, contributing to dense, rigid collagen formation that creates physical barriers. 77 Furthermore, this excess fluid hinders diffusion of nutrients and oxygen and leads to accumulation of waste and toxic metabolites in the TME, thereby disrupting NK cell metabolic function.

Hypoxia

Hypoxia heightens oxidative stress, interferes with energy production, and impairs essential processes that promote cellular function. Hypoxia impairs NK cell activation by decreasing expression of GZMB, perforin, and proinflammatory IFN-γ, as well as downregulating NK-cell-activating receptors. 78 , 79 Hypoxia also increases the degradation of NK-derived GZMB in hypoxic tumor cells by enhancing autophagy, and this process can be inhibited by beclin1. 80 The hypoxic TME accumulates immunosuppressive adenosine (ADO), a metabolite derived from ATP via CD73, a membrane-attached nuclease expressed on tumor cells ( Figure 1 ). 81 ADO impairs NK cell maturation and function by engaging A2A receptors (A2AR), fostering tumor progression via neovascularization and metastasis. 81

Acidosis, nutrient deprivation, and metabolic restrictions

Tumors exhibit heightened metabolic activity that enriches the TME with immunosuppressive byproducts such as prostaglandin E2 (PGE2) and lactic acid ( Figure 1 ). Lactate uptake disrupts key NK cell signaling pathways, including nuclear factor of activated T cells (NFAT) and mitogen-activated protein kinase (MAPK), while its intracellular accumulation induces acidification, reactive oxygen species (ROS) buildup, and apoptosis. 82 Concurrently, excessive nutrient consumption by tumors depletes glucose, amino acids, and fatty acids critical for NK metabolic fitness. 83 Together, these metabolic stressors undermine NK cell persistence and function, prompting a central focus of NK-immunotherapy research on enhancing NK metabolic resilience.

Immunosuppressive cells and soluble factors

The TME is rich in immunosuppressive cells, including regulatory T cells (T regs ), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages, and CAFs, which can blunt the efficacy of cytotoxic cell therapies ( Figure 1 ). Tumor cells and CAFs remodel the TME through the secretion of immunosuppressive cytokines such as TGF-β and IL-10. TGF-β inhibits mTOR signaling and suppresses glycolysis and oxidative phosphorylation in NK cells, 84 while both TGF-β and IL-10 downregulate activation receptors, such as NKG2D and CD16. 85 Glioblastoma (GBM) impairs NK cell cytotoxicity via the TGF-β axis contingent on cell-to-cell contact. 86 In acute myeloid leukemia (AML), our group demonstrated the TGF-β/SMAD/BATF axis epigenetically reprograms NK cells toward exhaustion. 87

PGE2 is another key TME immunosuppressive factor, inhibiting the production of pro-inflammatory cytokines and promoting MDSC and T reg expansion. 88 PGE2 also directly inhibits NK cell activation via their signaling receptors, reducing IFN-γ production, and impairing cytotoxicity. Cyclooxygenase (COX) inhibitors, which block PGE2 synthesis, enhance NK cell functionality and restore anti-tumor immunity. 88

NK cell memory

Compared to T cells, memory formation in NK cells is poorly defined. NK cells differentiate into memory subsets in viral infection and to guard against toxins, but this is not well described against cancer. In cancer, NK cell memory formation is often described as a hyperactivated state, rather than the long-term persistence, surveillance, or an antigen-specific clonal expansion seen in T cells. 25 This limitation leads to poor persistence after the initial challenge and can result in recurrence in patients with initial response. To combat this, researchers developed in vitro cytokine culture protocols such as IL-12, IL-15, and IL-18 cocktails that induce memory-like characteristics to enhance long-term killing and persistence. 25 , 26 Although promising, these approaches are not universally effective across tumor types. Overcoming this is key to the future success of NK-based immunotherapy.

Exhaustion and overactivation

Chronic antigen stimulation can induce CAR-T cell exhaustion, a dysfunctional state characterized by impaired cytotoxicity, reduced cytokine production, metabolic dysregulation, and expression of inhibitory receptors such as PD-1, TIM-3, LAG-3, and TIGIT. 89 Similarly, CAR-NK cell exhaustion manifests with upregulation of inhibitory receptors and checkpoints such as NKG2A, TIGIT, CD96, CIS and PD-1, as well as reduced cytotoxicity and cytokine production. 87

Challenges in target selection

Identifying suitable tumor-specific target antigens remains a major area of study for CAR-based immunotherapies. The heterogeneous nature of solid tumors can produce variable antigen specificity across individual tumors, limiting CAR-NK response. This is compounded by neoplastic evolution as many tumors mutate and adapt over time, leading to antigen downregulation, loss, or mutation that contribute to heterogeneity and immune escape. Due to dual mechanisms of direct CAR-mediated killing and indirect NK-intrinsic cytotoxicity obviating prior sensitization, CAR-NK cells may be theoretically better equipped to address antigen escape compared to CAR-T cells.

Conversely, CAR-engineered immune cells may recognize and target healthy tissue if the tissue expresses the target antigen, known as “on-target, off-tumor” side effects. This underscores the utility of tumor-specific antigens, exclusively expressed on tumor cells, rather than tumor-associated antigens, which are also found on healthy tissue, though at lower levels. Even with tumor-specific antigens, fratricide can develop in CAR-NK cells through the process of trogocytosis. 90 We demonstrated that trogocytosis-mediated fratricide can be prevented by engineering NK cells with a logic-gated dual-CAR system. 90 Here, one CAR targets a tumor-specific antigen and delivers an activating signal, while a second CAR recognizes an NK-specific self-antigen and delivers an inhibitory signal.

Novel preclinical approaches to enhance CAR-NK cell function against solid tumors

Current preclinical studies to enhance CAR-NK cell function in solid tumors aim to enhance infiltration and tumor targeting, overcome the immunosuppressive TME, boost CAR-NK persistence and potency, and ensure safety and efficacy ( Figure 1 ).

Deciphering and mitigating metabolic bottlenecks for CAR-NK cell therapy

The metabolic checkpoints described above create opportunities for intervention. In a preclinical model of NSCLC, CAR-NK cells targeting CD73 were devised to disrupt the CD73-adenosine axis, inhibiting immunometabolic reprogramming induced by adenosine produced by CD73, achieving tumor stasis. 91 Required for NK cell production of IFN-γ and GZMB, mTORC1 is a key metabolic regulator and plays an important role in NK cell fitness and immunity. 92 An approach that boosts Akt/mTORC1 axis and c-MYC signaling in NK cells is CRISPR-Cas9 deletion of CISH , which encodes the cytokine-inducible Src-homology-2-containing (CIS) protein, a negative regulator of IL-2 and IL-15 signaling in NK cells ( Figure 1 ). 93 We showed that CISH knockout enhances the metabolic fitness and anti-tumor activity of armored IL-15-secreting CB-derived CAR-NK cells. 94 Recently, we identified the transcription factor CREM as a key transcriptional checkpoint in NK cell activation. 95 CREM was induced in NK cells downstream of CAR activation or by IL-15, repressing a broad set of crucial NK cell effector genes, including cytotoxicity, calcium signaling, and regulatory function. CREM deletion enhanced CAR-NK cell potency by increasing chromatin accessibility for key NK-cell-activating transcription factors, improving NK cell proliferation and lifespan in vivo with enhanced glycolytic capacity. 95 Furthermore, sterol-regulatory-element-binding protein (SREBP) is another transcription factor that plays a positive role in cytokine-induced NK cell metabolic reprogramming by upregulating glycolysis and oxidative phosphorylation. 96 Temsirolimus, a mTOR signaling inhibitor, blocks HIF-1α translation and blunts tumor tolerance of hypoxia. 97 Thus, metabolic pathways can be targeted to improve CAR-NK cell metabolic fitness and potency.

Supporting expansion and survival by engineering cytokine support

To boost NK cell persistence in vivo , the infusion of exogenous proinflammatory cytokines such as IL-2 and IL-15 was investigated. However, their systemic administration may induce adverse effects, including capillary leak syndrome.

CAR constructs instituting proinflammatory cytokine support improve CAR-NK cell proliferation and persistence ( Figure 1 ). 98 CB-derived CAR-NK cells with IL-15 armoring show persistence up to a year in responder patients even with HLA-mismatch. 5 , 64 The therapeutic potential of IL-15 CAR-NK cells is further improved by the knockout of CISH to negate the cytokine-related immune checkpoint ( Figure 1 ). 94 Similarly, CAR-NK cells engineered with IL-12 have superior metabolic fitness and tumor control. 99 We demonstrated that IL-21 armoring enhances NK cell persistence and long-term in vivo efficacy against GBM. 65

NK cell persistence can also be improved by harnessing memory-like NK cell phenotypes. The cytokines IL-12, IL-15, and IL-18 induce memory phenotypes in NK cells with augmented anti-tumor activity and improved persistence. 25 , 100 The memory-like potentiation is synergistic with CAR signaling. Compared to memory-like NK cells alone, CD19-CAR-NK cells developed from memory-like NK cells exhibit enhanced survival and cytotoxicity against NK-resistant lymphoma, constituting up to 40%–90% of the NK cell population in the PB of NOD-SCID IL-2Rγ c null (NSG) mice 18 days post-adoptive transfer. 26 Similarly, memory-like CAR-NK cells targeting mesothelin in ovarian cancer showed robust tumor control in a preclinical model. 101 Memory-like unmodified NK cells in a clinical trial for head-and-neck cancer produced tumor regression in 50% of patients, 102 indicating that cytokine-induced memory-like (CIML) NK cell phenotypes have clinical promise.

Gene editing technologies to suppress inhibition and boost potency

The immunosuppressive factor TGF-β prevents pro-inflammatory cytokine secretion and NK cell degranulation and impairs metabolic fitness by downregulating mTOR pathways. 84 , 103 Thus, targeting TGF-β signaling may enhance CAR-NK cell activity ( Figure 1 ). TGFBR2 knockout prevents TGF-β1-induced allogeneic NK cell dysfunction in B-ALL and GBM models. 86 , 104 Knockout of TGFBR2 or expression of the dominant negative form of TGF-βR2 helps NK cells evade the immunosuppression mediated by TGF-β, restoring cytotoxicity and IFN-γ secretion, and not only boosts but is requisite for effective CAR-NK cell killing of hepatocellular carcinoma (HCC). 105 CAR-NK cells releasing peptides disrupting TGF-β1 signaling exhibited superior cytotoxicity against cancer spheroids with CAFs and in murine models. 106

Tumor cells may also upregulate inhibitory ligands that bind to NK inhibitory receptors, such as NKG2A, TIGIT, and TIM3, to dampen NK cell anti-tumor efficacy. Gene-editing-based knockdown or checkpoint-inhibitor-based blockade of inhibitory receptors prevent NK cell dysfunction ( Figure 1 ). 107 , 108 A recent study demonstrated that NKG2A knockout augmented the cytotoxicity of anti-CD33 CAR-NK cells. 109

Enhancing NK cell infiltration

Poor CAR-NK cell infiltration is a major challenge and may be enhanced by engineering chemokine signaling ( Figure 1 ). CAR-NK cells targeting estimated glomerular filtration rate variant III (EGFRvIII) with co-expression of CXCR4 showed improved chemotaxis toward U87-MG GBM cells secreting CXCL12, a ligand of CXCR4. 110 Similarly, CXCR1-overexpressing NKG2D-CAR-NK cells exhibited better infiltration in ovarian and hypopharyngeal tumors in xenograft models. 111 Oncolytic viruses may also enhance CAR-NK cell infiltration, with CCL5-armored vaccinia virus augmenting tumor homing of CCR5-engineered NK cells. 112 Autophagy blockade with the Food and Drug Administration (FDA)-approved autophagy inhibitor CQ increases CAR-NK cell migration in the GBM TME and improves mouse survival. 113 Local injection has also been investigated, such as delivering CAR-NK cells intracranially in GBM mouse models 70 , 71 , 114 as well as in human clinical trials. 72 , 73 These innovative strategies may improve CAR-NK cell infiltration and function.

Rational combinatorial therapeutic strategies

While CAR-NK cells exhibit robust anti-tumor responses in pre-clinical studies, combining them with other modalities may modulate the TME and enhance their effectiveness against solid cancers ( Figure 1 ).

Checkpoint inhibition

The major inhibitory receptors expressed by NK cells are NKG2A, TIGIT, TIM3, and LAG3, ligands for which are commonly upregulated in several solid tumors. 107 , 108 , 109 Their blockade prevents NK cell dysfunction in multiple solid tumor models. 107 , 108 , 109 Moreover, PD-L1-specific CAR-NK cells and anti-PD-1 nivolumab showed synergistic anti-tumor responses in a nasopharyngeal-carcinoma-patient-derived xenograft (PDX) humanized mouse model. 115 Thus, combining checkpoint inhibitors targeting inhibitory ligands may prevent CAR-NK cell dysfunction.

Radiation therapy and chemotherapy

While radiation therapy (RT) and chemotherapy are widely used as standard therapies to induce apoptosis of cancer cells, these treatments also upregulate activating ligands to enhance tumor cell killing by NK cells. RT via Iodine-125 ( 1 25 I) brachytherapy combined with ROBO1-specific CAR-NK cells enhanced necrosis in a pancreatic tumor mouse model. 116 In mouse models of rhabdomyosarcoma, RT improved homing of EGFR-CAR-NK cells. 117 Similarly, CD133-targeting CAR-NK-92 cells exhibited superior anti-tumor efficacy when combined with the chemotherapy cisplatin, and cisplatin did not impair CAR-NK cell viability and cytotoxicity. 118 Thus, combining CAR-NK cells with RT or chemotherapy may boost CAR-NK cell anti-tumor responses in solid neoplasms.

Targeted therapy

Targeted therapies, including kinase inhibitors, proteasome inhibitors, and STING agonists, can enhance CAR-NK cell efficacy against solid tumors. In a colon cancer model, synergy was seen with EpCAM-CAR-NK cells and regorafenib, a multi-kinase inhibitor. 119 STING agonist Rocaglamide increased NK cell infiltration and activation within the TME and improved tumor control. 120 In renal cell carcinoma (RCC), EGFR-specific CAR-NK-92 cells showed synergistic anti-tumor activity in vitro and in vivo when combined with cabozantinib, a standard-of-care systemic therapy for RCC. 121

Oncolytic viruses

Oncolytic viruses may directly kill cancer cells and indirectly stimulate anti-tumor responses by providing proinflammatory cytokines and propagating antigens within the TME. 70 , 112 In multiple GBM mouse models, EGFR-specific CAR-NK cells synergistically reduced tumor growth and improved survival when combined with an IL-15/IL-15 Rα-expressing oncolytic virus, 70 suggesting their promise as a combination therapy.

Multi-specific and tandem CARs to target multiple tumor antigens

Tumor antigens with high specificity and consistent expression on cancer cells are required to develop effective CAR-NK cells, but this remains a significant hurdle. To prevent antigen escape and avoid off-target effects of CAR-NK cell therapy against solid cancers, dual or multi-specific CARs can be designed to target more than one tumor antigen simultaneously.

CAR-NK cells expressing anti-CD19 CAR and high-affinity non-cleavable CD16 enabled high-affinity binding to monoclonal antibodies and mediated ADCC. Multiple antigens targeted with this approach demonstrated superior anti-tumor responses in mouse models compared to targeting a single antigen. 122 These CAR-NK cells were combined with therapeutic antibodies to target additional antigens to overcome antigen loss and tumor heterogeneity in B cell malignancies, which may provide a similar advantage in the context of solid tumors. Similarly, a preclinical study used NK92MI to derive a tissue factor (TF)-targeting antibody-like immunoconjugate on CAR-NKs with the CAR co-expressing CD16 to mediate ADCC against triple-negative breast cancer (TNBC) cells. 123 The clinical potential of harnessing ADCC to enhance the therapeutic efficacy of adoptive NK cell therapy was recently demonstrated in a phase I clinical trial showing potent anti-tumor activity of CB-derived NK cells in combination with a bispecific innate cell engager that binds to CD16 on NK cells and CD30 on tumor cells. The trial showed an overall response rate of 92.9% and a complete response rate of 66.7% in patients with relapsed/refractory CD30 + lymphoma. 124

Dual-targeting α-CD73 and α-GD2 CAR-NK cells against GBM with a third functional moiety only activated in the TME prevented NK cell immunosuppression. These CAR-NK cells locally release an antibody fragment that prevents the enzymatic activity of CD73, reducing adenosine concentration ( Figure 1 ). 113

To improve the safety of CAR-NK cells, a suicide switch may be integrated into the CAR construct. Our group showed the feasibility of integrating an inducible caspase-9 in the construct to selectively deplete CAR-NK cells upon receipt of AP1903 (Rimiducid) in the context of toxicities. 14

Current clinical trials of CAR-NK cells in solid tumors

Worldwide, the number of CAR-NK cell clinical trials is steadily expanding. A filtered query in ClinicalTrials.gov for “CAR-NK cells” yields 124 clinical trials, excluding trials using CAR-NKT cells or erroneously included CAR-T cells. There were 15 CAR-NK cell trials for autoimmune diseases and one trial targeting COVID-19. Among anti-neoplastic CAR-NK cell clinical trials, the majority are for hematological malignancies with 69 total clinical trials: 22 are recruiting, 6 are active but not yet recruiting, and 3 are completed, of which 2 have published outcomes for CAR-NK cells targeting CD19 ( Figure 2 A). 5 , 53 There are 39 CAR-NK cell trials against solid tumors, with one having published early results ( Figure 2 B). Evidently, there has been growing interest in exploring the therapeutic potential of CAR-NK cell therapies in solid tumors, with an expanding roster of early-phase clinical trials and a growing diversity in targeted antigens and tumor types ( Table 1 ; Figures 2 C and 2 H).

Across all trials, the majority were from China ( Figure 2 D). Safety is the primary endpoint, supplemented by secondary endpoints of efficacy, quality of life, and biological correlates including NK cell persistence. Several trials described outpatient administration of CAR-NK cells, highlighting their safety. The majority are phase I or early-phase I, with some phase I/II trials ( Figure 2 E). The cell source for CAR-NK cells is not specified for most studies (35.9%), but where named mostly include CB (25.6%), followed by NK-92 cells (17.9%), PBMCs (17.9%, mostly autologous sources), or iPSCs (2.6%) ( Figure 2 F). Below we summarize by disease subtype the major developments involving CAR-NK cells in solid tumors. We expect more knowledge will arise as more clinical trials emerge with time ( Figure 2 G).

Glioblastoma

The most mature efforts thus far with CAR-NK cells in solid tumors are in GBM. Preclinical data in GBM include CAR-NK cells targeting IL-13Rα2 or EGFR and its variant EGFRvIII, 110 , 114 HER2, 71 and the immune checkpoint inhibitors B7-H3 125 and HLA-G 126 or devising CD73.mCAR pNK cells to target autophagy and improve NK trafficking to GBM tumors ( Figure 2 H). 113 One accruing clinical trial ( NCT04991870 ) incorporates reprogramming the TME by applying CB-derived NK cells rationally engineered via CRISPR/Cas9 to delete both TGFBR2 and NR3C1 , the gene encoding the glucocorticoid receptor, based on preclinical evidence. 86 A Frankfurt group launched CAR2BRAIN ( NCT03383978 ) to investigate the NK-92/5.28.z cell therapy product targeting HER2 in a first-in-human phase I clinical trial for recurrent HER2-expressing GBM. 21 This experience represents the first report of CAR-NK cell therapy for a solid tumor in a series of patients.

In CAR2BRAIN, the CAR-NK cells were irradiated as a safety measure, which is standard for NK-92 products. In preclinical assessments, the NK-92/5.28.z cells exhibited robust cytotoxicity in hypoxic environments (as low as 0.1%) and at high concentrations of TGF-β, which are hallmark hostile features of the TME in GBM. The irradiated CAR-NK cells were injected into the cavity margins during surgery that was performed for the relapsed GBM. Although the trial planned to enroll 42 patients, the results for nine subjects with IDH-WT GBM was published in 2023, and it is currently not recruiting. 21 The CAR-NK cells had a favorable safety profile, with no reported dose-limiting toxicities (DLTs), no CRS, or ICANS at the maximum feasible dose (MFD) of 1 × 10 8 cells, which was the highest planned dose level administered. Regarding outcomes, five of nine patients showed stable disease, and four patients had progressive disease. Pseudoprogression at the injection site was seen in two patients, suggesting a treatment-induced immune response. Both patients received the highest dose of CAR-NK cells and had progression-free survival (PFS) of 37 weeks with promising overall survival (OS) of 1.9 and 2.6 years. For the overall cohort, the median PFS was 7 weeks, and the median OS was 31 weeks, aligning with historically poor survival in GBM. There was no antigen escape on histological analysis of post-treatment specimens. The pre-treatment presence of intratumoral CD8 + T cells in the recurrent tumor correlated with improved PFS and OS. Dose expansion cohorts are underway with up to 12 additional weekly intracranial doses of NK-92/5.28.z cells through an implanted catheter and with concomitant delivery of ezabenlimab, a monoclonal antibody targeting PD-1, based on preclinical experiments showing an invigorating combination of the two treatment modalities. 127 , 128

Ovarian cancer

Representing the most common solid tumor being investigated with CAR-NK cells, there are currently seven accruing trials for ovarian cancer, particularly platinum-resistant ovarian cancer. The studies commonly list intraperitoneal delivery of CAR-NK cells. Preclinical models of ovarian cancer have utilized CAR-NK cells targeting mesothelin, 129 folate receptor alpha (FRα), 130 and NKG2D ligands ( Figure 2 H). 131 Currently enrolling clinical trials in patients with advanced ovarian cancers are evaluating the safety and preliminary efficacy of CAR-NK cells targeting trophoblast cell surface antigen 2 (TROP2) via NCT05922930 , mesothelin ( NCT05410717 , NCT03692637 , and ChiCTR2100048100), NKG2D ligands ( NCT05776355 ), MIC-A/B ( NCT06342986 ), and Claudin6, GPC3, or AXL ( NCT05410717 , also for endometrial cancer).

As a novel therapeutic approach, FT536 is an off-the-shelf CAR-NK cell therapy derived from iPSCs designed to target the stress proteins MIC-A/MIC-B ( NCT06342986 ). 132 By binding their α3 domain, the CAR-NK cells circumvent a known mechanism of tumor immune escape caused by shedding of the α1 and α2 domains, which can be overcome by binding the α3 domain to prevent MIC-A/B shedding. 32 , 133 Other enhancements include a high-affinity, non-cleavable CD16 receptor, an IL-15 receptor fusion, and CD38 gene deletion to increase effectiveness and persistence in high oxidative stress environments found in the TME. While this trial focuses on cancers of the female reproductive system, other prospective cancers include non-small cell lung cancer (NSCLC), colorectal cancer, and cancers of the head-and-neck, stomach, breast, and pancreas. 132

Pancreatic cancer

Compared to other cancers of the gastrointestinal tract, pancreatic ductal adenocarcinoma (PDAC) has a larger footprint in the domain of CAR-NK cell trials against solid tumors. Among seven clinical trials investigating CAR-NK cells, therapeutic targets include TROP2 ( NCT05922930 ), Claudin18.2 ( NCT06464965 ), eGR1 ( NCT06816823 ), MUC1 ( NCT02839954 ), and NKG2D ligands in two trials— NCT06478459 with intratumoral injection via endoscopic ultrasound as well as intravenous (i.v.) infusion, and NCT06503497 with i.v. infusion of the CAR-NK cells ( Figure 2 H). Preclinical investigation of CAR-NK cells targeting ROBO1, including with 125 I seed brachytherapy, 116 served as the basis for two clinical trials using ROBO1-specific CAR-NK cells derived from NK-92 cells in pancreatic cancer ( NCT03941457 and NCT03940820 ). In a report from NCT03941457 , one patient with de novo metastatic PDAC to the liver was treated upfront with serial percutaneous injections of the ROBO1-CAR-NK cells to the liver metastasis, twice weekly for the first month, as well as with weekly i.v. infusions of the CAR-NK cells for 5 months. 73 He had control of the pancreatic lesion and liver metastasis over this period, before developing disease progression to which he finally succumbed 8 months after diagnosis. 73 FRα and death receptors 4 and 5 (DR 4/5) are overexpressed in pancreatic cancer and are being investigated as preclinical targets for cytotoxic ligand-loaded CAR-NK cells that mediate tumor-selective apoptosis. 134 Mesothelin-targeting CAR-NK cells generated via a transposon system have also been described ( Figure 2 H). 135 , 136

Colorectal cancer

In colorectal cancer, NKG2D ligands ( NCT05528341 and NCT05248048 ) and TROP2 ( NCT06358430 ) have been leveraged as tumor antigens, but preclinical targets have included EpCAM 119 and CEA 137 ( Figure 2 H). Representing the first reported experience of CAR-NK cell therapy for solid tumors in humans, NCT03415100 issued a preliminary report in 2018 of three patients treated with autologous or allogeneic haploidentical PBMC-derived NKG2D ligand-targeting CAR-NK cells with DAP12 co-stimulation. 72 Here, the NKG2DL-CAR was delivered via an RNA electroporation approach to enable transient CAR expression as a risk mitigation strategy. No ≥ grade 3 adverse effects were observed. Only grade 1 CRS was seen without any neurologic symptoms observed. Impressively, the trial reported favorable safety and early signals of efficacy, such as tumor cell reduction in ascites fluid, ascites control, and even complete metabolic response of an injected colorectal cancer liver metastasis in one patient who received ultrasound-guided percutaneous injection as well as intraperitoneal delivery of the CAR-NK cells. In this patient, the liver metastasis subjected to local CAR-NK cell injection showed rapid regression by ultrasound in 4 days, loss of FDG-avidity at 4 weeks, and no viable cancer on pathology. 72 Of note, unmanipulated liver metastases continued to harbor viable tumor. Overall, this experience serves as proof of principle demonstrating the therapeutic value of image-guided percutaneous delivery of CAR-NK cells as a minimally invasive and repeatable procedure, driving robust local anti-tumor responses.

Other gastrointestinal cancers

Clinical trials are being deployed using CAR-NK cells that recognize tumor antigens such as Claudin18.2 for gastric cancer ( NCT06464965 ) and MUC1 for HCC ( NCT02839954 ). Other preclinical targets include c-MET 138 and glypican-3 (GPC3) 139 for HCC and mesothelin for gastric cancer ( Figure 2 H). 140

Lung cancer

Clinical trials devoted to CAR-NK cell therapy for lung cancer primarily comprise of NSCLC with target antigens such as MUC-1 ( NCT02839954 ) or TROP2 ( NCT06066424 ). Preclinical targets that have been investigated include B7-H3 141 as well as CD73 to blunt immunometabolic shifts via impairment of adenosinergic metabolism driven by CD73. 91 There is also a clinical trial enrolling patients with extensive-stage small cell lung cancer (ES-SCLC), utilizing CAR-NK cells targeting DLL3 ( NCT05507593 ), supported by preclinical studies ( Figure 2 H). 142

An interesting approach for patients with NSCLC in NCT03656705 involves NK-92 cells expressing a chimeric costimulatory converting receptor (CCCR) consisting of a PD-1 extracellular domain, NKG2D transmembrane and cytoplasmic domains, and a 4-1BB costimulatory cytoplasmic domain. 143 Here, the inhibitory programmed cell death protein 1 (PD-1) signal is converted into an activating cascade, reversing immunosuppression mediated by PD-1. Notably, the second patient enrolled in this study developed the first and only reported case of more severe CRS with CAR-NK cell therapy, characterized by marked serum levels of TNF-α and IFN-γ, raising the possibility that this unique construct design may have led to NK cell hyperactivation, resulting in the overproduction of these cytokines. 143

Breast cancer

Breast cancer is another area of active investigation, especially for more aggressive subtypes like HER2-positive and TNBC. Preclinical studies have supported CAR-NK cells targeting HER2, 144 EGFR, 145 tissue factor (TF), 123 and EpCAM ( Figure 2 H). 146 Three clinical trials are specifically recruiting for breast cancer but only one clinical trial ( NCT06066424 ) names the antigen being targeted, which is TROP2.

Head-and-neck cancer

NK cells have prominence in head-and-neck (HN) cancer outcomes. 147 Recognizing the centrality of radiotherapy (RT) in the treatment of HN cancer, we recently opened a first-in-human trial for unresectable HN cancer treated with preconditioning stereotactic RT followed by TROP2-CAR-NK cells genetically modified by deletion of TGFBR2 ( NCT07101432 ). Recently published, NCT04290546 was a phase I study in recurrent or metastatic HN cancer patients, examining the safety and preliminary efficacy of allogeneic PBMC-derived CIML NK cells. 102 The NK cells were delivered along with N-803, an IL-15 superagonist, after lead-in ipilimumab, and led to tumor regression in 50% of the patients, which notably associated with persistent CD56 dim CD16 + CIML NK cell expansion. A sequel trial, NCT04847466 , is now recruiting HN cancer patients with the primary objective of evaluating complete and partial response rates following treatment with genetically modified PD-L1 targeting high-affinity NK (t-haNK) cells along with pembrolizumab and N-803 ( Figure 2 H).

Rare cancers

Clinical efforts in rare cancer subtypes include anaplastic thyroid cancer with NKG2D-CAR-NK cells ( NCT06856278 ), melanoma using preferentially expressed antigen in melanoma (PRAME) TCR-engineered NK cells ( NCT06660420 ) and CD70-targeting CAR NK cells for RCC and mesothelioma ( NCT05703854 ), and sarcomas, including osteosarcoma (also in NCT05703854 with CD70-specific CAR-NK cells) and myxoid liposarcoma using an affinity-enhanced TCR against NY-ESO-1 ( NCT06083883 ) ( Figure 2 H). Unlike CARs that recognize mostly surface antigens, TCRs can target intracellular proteins presented as peptide-HLA complexes, expanding targets to lineage transcription factors, cancer-testis antigens, and other neoepitopes. Early-phase clinical trials in these cancers seek to establish safety, tolerability, and early signals of efficacy in these less-studied solid tumors in urgent need of novel therapeutic options, laying groundwork for future advancement.

Side effects of cell therapy using NK cells in the clinic

To date, completed clinical trials of CAR-NK cells have described mostly manageable adverse effects including transient cytopenias and mild infusion reactions or ≤grade 2 CRS ( Table 2) . 5 , 21 , 53 , 148 However, as a first report of CRS in CAR-NK cell therapy, there was one case report of more severe CRS observed in CAR-NK cells in a patient with NSCLC, where NK-92 cells were modified to express a chimeric converting construct whereby PD-1 binding led to a NKG2D-mediated activating signal. 143 CRS grade was not specified, though details disclosed correlate with grade 3 CRS. This NK-tailored chimeric receptor enabled transformation of the negative PD-1 signal to an activating signal, reversing immunosuppression by PD-1. The patient had a 10-fold increase in serum levels of IFN-γ and TNF-α, suggesting the unique construct led to NK cell overactivation.

Outside of this incidence, there have not been other reports of ≥grade 3 CRS or any evidence of ICANS, tumor lysis syndrome (TLS), or GvHD, which can be observed with CAR-T cell therapy. One report of CD33-CAR-NK cells derived from NK-92 cells described fever and grade 1 CRS. 149 Another report of iPSC-derived NK cells targeting CD19 (termed FT596) described grade 1 CRS in one of eight patients (6%) receiving FT596 cells alone or 13% patients developing ≤grade 2 CRS if patients received FT596 with rituximab. In contrast, among patients undergoing CAR-T cell therapy, ≥grade 1 CRS occurs in 57%–93%, and ≥grade 3 CRS occurs in 13%–32% of patients. 2 Thus, both the severity and incidence of CRS is lower with CAR-NK cells relative to CAR-T cells. The milder side effect profile from NK cell adoptive therapy is thought to be due to their shorter lifespan and lower cytokine production but this may also indicate reduced efficacy for unmodified NK cells. 150 To further minimize potential risks and bolster the safety of CAR-NK cells, inducible suicide genes, such as iCas9, have been incorporated in some clinical products to initiate rapid and controlled cell death of the modified immune cells. 14

Overall, the safety profile of CAR-NK cell therapy is favorable, but careful monitoring during treatment and review of outcomes in prospective clinical trials remain important. Specifically, it appears that more severe cases of CRS may be observed with CAR-NK cells in special contexts where unique constructs or potentially when vigorous expansion methods are employed.

Conclusions

In summary, the landscape of CAR-NK clinical trials is rapidly diversifying across both hematologic and solid tumors, with a strong focus on improving safety, broadening accessibility, and refining efficacy through next-generation engineering strategies and combination approaches. While favorable outcomes have been achieved in hematological malignancies, translating this success into the solid tumor setting remains an active area of investigation, with persistent challenges posed by limited in vivo persistence, complex antigen landscapes, trafficking hurdles, and the immunosuppressive TME. Clinical progress will require advances in cell engineering to promote persistence and efficacy, immunometabolic modulation for enhanced resilience, and rational approaches rooted in biological underpinnings. Nonetheless, early clinical trials are promising, particularly in terms of tolerability and very preliminary efficacy signals. Ongoing studies across a spectrum of malignancies will be instrumental in defining the future role of CAR-NK therapy in treating solid tumors. Across all indications, a consistent theme emerging from clinical data is the superior safety profile of CAR-NK therapies compared to traditional CAR-T cell approaches. Most trials to date, including those employing allogeneic sources such as CB- or iPSC-derived NK cells, have reported lower incidences and less severe adverse effects such as CRS and no GvHD, positioning CAR-NK as a viable off-the-shelf option for broader patient populations with anticipated lower financial toxicity and rich developmental ground for future deployment.

Acknowledgments

The development of this manuscript did not specifically require any funding. G.S.M. is supported by a K12 Calabresi Scholars Award (5K12CA088084). M.D. is supported by an R01 grant (R01-CA280827-01), a Leukemia Specialized Program of Research Excellence (SPORE) Grant (P50CA100632), by grants from the Society for Immunotherapy of Cancer (SITC), Andrew Sabin Family, and from the SPORE developmental research program in Leukemia.

Author contributions

M.D. and G.S.M. supervised the creation of the review. G.S.M. rendered tables and figures. G.S.M., M.F.H., M.M., S.T., N.P.O., and M.D. wrote the manuscript. All authors edited the manuscript.

Declaration of interests

M.D. has a financial conflict of interest with Takeda Pharmaceutical for CAR-NK cell technology and participates on the scientific advisory board of Cellsbin, Aurigene, and Bruker Cellular Analysis.

Footnotes

Supplemental information can be found online at https://doi.org/10.1016/j.xcrm.2026.102881 .

Contributor Information

Rafet Basar, Email: rbasar@mdanderson.org.

May Daher, Email: mdaher@mdanderson.org.

Supplemental information

Document S1. Tables S1 and S2

Document S2. Article plus supplemental information

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