Natural killer (NK) cell-based chimeric antigen receptor (CAR) therapy is emerging as a promising alternative to CAR-T cell treatment, offering comparable efficacy with significantly improved safety profiles and potential for off-the-shelf accessibility. Recent clinical trials demonstrate the therapeutic potential of CAR-NK cells while highlighting key advantages over traditional CAR-T approaches.
Clinical Efficacy Matches CAR-T Performance
Early-stage clinical trials are demonstrating that CAR-NK cell therapies can achieve response rates comparable to established CAR-T treatments. In a phase 1/2 trial of anti-CD19 CAR-NK cells derived from cord blood, 11 patients with relapsed or refractory CD19-positive hematologic malignancies achieved an objective response rate of 73% within one month of treatment, with nearly all responses being complete responses.
"The responses that we observed were pretty similar to what you would get with [autologous CD19 CAR] T cells," noted Katy Rezvani, MD, PhD, professor of medicine at The University of Texas MD Anderson Cancer Center. Extended results from 37 patients showed an objective response rate of 48.6% at day 30 and day 100, with complete responses observed in 29.7% of patients by day 100.
In acute myeloid leukemia, the anti-NKG2D CAR-NK therapy NKX101 demonstrated promising early results in a phase 1 study, with 67% of patients achieving complete response or complete response with incomplete hematologic recovery. Two patients achieved minimal residual disease negativity after only one treatment cycle.
Superior Safety Profile Eliminates Major Toxicities
The most significant advantage of CAR-NK cell therapy lies in its safety profile. Unlike CAR-T cell treatments, CAR-NK therapies have not produced cases of graft-versus-host disease (GVHD), cytokine release syndrome (CRS), or immune effector cell-associated neurotoxicity syndrome (ICANS) in clinical trials to date.
CAR-NK cells release different cytokines compared to CAR-T cells, preventing the cytokine storm that leads to CRS. The shorter lifespan of CAR-NK cells and specificity of antibody-based CAR targeting also limit on-target, off-tumor toxicity effects that can occur with CAR-T therapy.
The safety advantages stem from NK cells being part of the innate immune system and not requiring HLA matching, which eliminates the risk of GVHD when using allogeneic cells. This fundamental difference allows CAR-NK cells to function as an "off-the-shelf" therapy without the manufacturing delays and costs associated with personalized CAR-T cell production.
Advanced Engineering Strategies Enhance Therapeutic Potential
Researchers are developing sophisticated approaches to optimize CAR-NK cell therapy through structural modifications and enhanced production methods. Dual CAR-NK cells that express two independent receptors provide greater specificity in recognizing cancer cells while preventing immune escape through antigen loss.
The development of FT596, a multi-targeting CAR-NK cell possessing anti-CD19 CAR, non-cleavable CD16 receptor, and IL-15/IL-15α, represents an advancement in enhancing both cancer-killing ability and persistence of CAR-NK cells. Bispecific CAR-NK cells targeting multiple antigens simultaneously, such as anti-CD19-CD22 constructs, have demonstrated effective lysis of B-cell lymphomas.
Universal CAR systems offer another promising strategy, allowing CAR-NK cells to be activated only upon coupling with specific target molecules, providing greater control over therapeutic activation and reducing potential off-target effects.
Multiple Cell Sources Enable Scalable Production
CAR-NK cells can be derived from various sources, each offering distinct advantages for clinical application. Cord blood-derived NK cells possess higher proliferation capacity and better homing ability compared to peripheral blood NK cells, while being less immunogenic due to reduced T-cell contamination.
Induced pluripotent stem cell (iPSC)-derived NK cells represent an emerging source that could provide unlimited supply for off-the-shelf therapy. Although iPSC-derived NK cells require more complex manufacturing procedures, they offer consistent homogeneity and high proliferative capacity without requiring donor collection.
The NK-92 cell line and its derivatives provide another scalable source, with modifications such as NK-92ci and NK-92mi cells that express IL-2, and high-affinity NK-92 cells (haNK) that incorporate CD16 receptors to mediate antibody-dependent cellular cytotoxicity.
Overcoming Therapeutic Challenges Through Innovation
Despite promising results, CAR-NK cell therapy faces challenges including limited persistence, inhibitory receptor suppression, and immunosuppressive tumor microenvironments. Researchers are addressing these limitations through multiple strategies.
Cytokine supplementation with IL-15, IL-21, and IL-18 enhances NK cell activation, proliferation, and persistence. IL-15 co-expression with CAR constructs has shown particular promise, with anti-CD123-2B4-CD3 CAR-NK cells demonstrating increased persistence and enhanced anti-tumor ability against acute myeloid leukemia when co-expressed with secretory IL-15.
Targeting inhibitory receptors represents another approach to enhance CAR-NK cell function. Monoclonal antibodies such as IPH2102 (lirilumab) that block killer cell immunoglobulin-like receptors (KIRs) and monalizumab targeting NKG2A are being investigated to unlock NK cell inhibition and activate cancer-killing mechanisms.
Combination Strategies Expand Therapeutic Potential
The combination of CAR-NK cells with other therapeutic modalities is showing enhanced efficacy. AFM13, a tetravalent bispecific antibody targeting CD30 and CD16a, combined with cord blood-derived NK cells achieved a 93% objective response rate and 67% complete response rate in heavily pretreated patients with CD30-positive lymphomas.
NK-cell engagers, including bispecific killer cell engagers (BiKE) and trispecific killer cell engagers (TriKE), bridge NK cells with cancer cells more effectively. These constructs target various NK cell receptors including CD16a, NKG2D, and others to enhance cancer elimination capabilities.
Clinical Development Focuses on Solid Tumors
Current clinical development includes 49 registered trials of CAR-NK cell therapy, with 36 focusing on hematologic malignancies and 13 targeting solid tumors. The expansion into solid tumor applications represents a critical frontier, as the immunosuppressive tumor microenvironment presents unique challenges for NK cell function.
Strategies to overcome solid tumor barriers include engineering CAR-NK cells with chemokine receptors such as CXCR1 to improve trafficking into tumor sites, and targeting immunosuppressive factors like TGF-β through dominant negative receptors co-expressed with CAR constructs.
Manufacturing and Regulatory Considerations
The FDA has established guidelines for CAR-NK cell product development, emphasizing Good Manufacturing Practices (GMP) compliance for chemistry, manufacturing, and control of CAR products. These guidelines address general CAR design and development, as well as clinical and non-clinical recommendations to ensure product safety and quality.
Optimal donor selection has emerged as a critical factor for cord blood-derived CAR-NK cells. Research indicates that cord blood units frozen within 24 hours of collection with nucleated red blood cell counts below 80 million produce superior therapeutic outcomes, with one-year overall survival rates of 94% versus 48% for optimal versus suboptimal donors, respectively.
The field of CAR-NK cell therapy represents a paradigm shift in cancer immunotherapy, offering the potential for safer, more accessible treatment options while maintaining therapeutic efficacy comparable to existing CAR-T approaches. As clinical trials continue to demonstrate promising results and manufacturing processes become standardized, CAR-NK cells may provide a transformative approach to cancer treatment that combines the benefits of personalized medicine with off-the-shelf accessibility.
