CAR-NK Cells: A Promising Immunotherapeutic Approach for Breast Cancer Treatment

 

A recently published article in Molecular Therapy, authored by a research team led by Dr. Winfried S. Wels at Goethe University Frankfurt in collaboration with scientists from multiple research institutes, presents a comprehensive investigation into ErbB2-specific CAR-engineered natural killer cells (NK-92/5.28.z). The study evaluates their therapeutic potential using an advanced breast cancer organoid model. This essay offers a critical analysis of the study’s major contributions, highlighting the relevance of the organoid model, the antitumor activity of the CAR-NK cells, and the broader translational implications of this innovative immunotherapeutic strategy.

Targeting ErbB2/HER2 with Precision: The Promise of Off-the-Shelf CAR-NK Cells in Breast Cancer Therapy

Breast cancer is the most frequently diagnosed cancer in women worldwide and remains a leading cause of cancer-related deaths. Around 20–25% of cases involve overexpression of ErbB2 (HER2), a receptor tyrosine kinase that drives cell growth and survival. HER2 overexpression or mutation is linked to aggressive tumor behavior and poor prognosis. Although targeted therapies like trastuzumab, pertuzumab, tyrosine kinase inhibitors, and antibody-drug conjugates (ADCs) have improved outcomes, treatment resistance and failure remain major obstacles, highlighting the need for new therapeutic approaches.

 Adoptive cell immunotherapy is gaining traction as a promising cancer treatment. While CAR-T cell therapy has been successful in blood cancers, its application to solid tumors remains challenging. Natural killer (NK) cells offer an alternative due to their ability to eliminate cancer cells without prior sensitization or antigen presentation. Their low risk of graft-versus-host disease makes them suitable for allogeneic, off-the-shelf use. Engineering NK cells with chimeric antigen receptors (CARs) enhances their cytotoxicity, combining innate and antigen-specific tumor targeting.

Organoid Model Development: A Revolutionary Approach to Breast Cancer Research

A key aspect of this study is the development of an advanced organoid model that closely mimics ErbB2-positive breast cancer progression. Traditional 2D cultures fail to reflect the structural and biological complexity of tumors, whereas this 3D organoid system better replicates tumor architecture and the microenvironment.

The researchers created mammary organoids from primary epithelial cells isolated from CKP (CC10-CreERT2 Kras^LSLG12Vgeo/WT Tp53^fl/fl) mice, engineered to allow inducible Kras^G12V expression and Tp53 deletion. Following enzymatic digestion and Matrigel embedding, the organoids exhibited compartmentalization with luminal K8/K18-positive cells surrounded by K14-positive basal myoepithelial cells, closely resembling the native mammary gland.

To model HER2-positive cancer, CKP organoids were transduced with a lentiviral vector encoding human ErbB2 and Cre recombinase, producing EC-CKP organoids. This led to loss of p53, sustained MAPK signaling via Kras^G12V, and increased phosphorylated Erk1/2 and c-Raf, key features of ErbB2-driven tumors. These organoids underwent malignant transformation, forming highly branched structures with larger, multinucleated cells and enlarged nuclei. Proliferation increased significantly, with Ki67-positive regions rising from 26% to 42%. Elevated γ-H2AX levels indicated increased DNA double-strand breaks.

This organoid model effectively replicates both the molecular and structural features of ErbB2-positive breast cancer and enables dynamic tracking of tumor evolution, as shown by the emergence of more aggressive phenotypes after in vivo passaging.

CAR-NK Cell Technology: Harnessing the Power of Innate Immunity

The NK-92/5.28.z CAR-NK cell line represents a next-generation immunotherapy that harnesses innate immunity. NK cells kill tumor cells through granule release, death receptor signaling, and cytokine secretion, without prior antigen exposure. Unlike T cells, they recognize stressed or transformed cells via diverse activating receptors.

The NK-92 line, derived from a lymphoma patient, has been optimized for clinical use. Its 5.28.z variant expresses a CAR targeting ErbB2, featuring an FRP5-derived extracellular domain and intracellular signaling regions that activate NK cells upon contact with ErbB2-positive targets.

A major advantage of NK-92/5.28.z cells is their off-the-shelf availability. Unlike patient-specific CAR-T cells, they can be mass-produced and cryopreserved. Their lack of a T-cell receptor reduces graft-versus-host risk, allowing safe allogeneic use. These engineered NK cells combine natural and CAR-driven cytotoxicity, enhancing tumor targeting. Clinical trials in glioblastoma have shown their safety, with no severe cytokine release or neurotoxicity.

After showing efficacy in solid tumor models, NK-92/5.28.z cells are now in a phase I trial for ErbB2-positive glioblastoma (CAR2BRAIN; NCT03383978). This study builds on this by testing their potential in breast cancer using a 3D organoid model.

In Vitro Findings: Potent Cytotoxicity Against Breast Cancer Organoids

This study presents strong in vitro evidence for the cytotoxicity of NK-92/5.28.z cells against ErbB2-positive breast cancer, using both dissociated cells in 2D and intact organoids in 3D culture.

In 2D co-cultures with EC-CKP cells, NK-92/5.28.z cells showed dose-dependent, specific cytotoxicity, whereas unmodified NK-92 cells had little effect. Neither cell type affected ErbB2-negative CKP cells, confirming target specificity.

Upon exposure to EC-CKP cells, NK-92/5.28.z cells showed activation through CD107a expression, CD69 upregulation, and IFN-γ and TNF-α secretion. These responses were absent in parental NK-92 cells. Time-lapse imaging confirmed that CAR-NK cells formed synapses with EC-CKP cells, directing lytic granules toward the target and inducing apoptosis. No such interactions occurred with ErbB2-negative or unmodified cell pairings.

In 3D assays, NK-92/5.28.z cells showed limited short-term (4-hour) killing, likely due to restricted access within the organoids. However, after 12 hours, they effectively lysed organoids, even at low effector-to-target ratios. Imaging revealed that CAR-NK cells accumulated at the periphery and degraded tumor layers from the outside in. Smaller organoids were nearly eliminated, while larger ones showed partial destruction. These results highlight the importance of prolonged exposure for effective tumor clearance and may inform clinical dosing strategies.

In Vivo Validation: Efficacy Against Aggressive, Treatment-Resistant Tumors

The study’s in vivo section modeled tumor evolution and resistance through serial passaging. EC-CKP organoids transplanted into NSG mice formed tumors, and cells from these tumors cultured into secondary organoids developed an EpCAM^-/low phenotype, indicative of epithelial-to-mesenchymal transition (EMT).These cells showed spindle-shaped morphology, cell protrusions, reduced E-cadherin, elevated N-cadherin and vimentin, and expressed the EMT driver ZEB1. They also contained a CD44^high/CD24^low cancer stem cell population and formed more aggressive tumors in mice.

Although resistant to treatments like 5-fluorouracil and radiation, these cells retained high ErbB2 levels and remained vulnerable to NK-92/5.28.z cells. In mice, peritumoral injections of CAR-NK cells on days 6, 9, 12, and 15 significantly slowed tumor growth. By day 17, tumor weight was markedly reduced, and histology confirmed CD45+ CAR-NK cell infiltration near tumor margins. These findings support the effectiveness of ErbB2-targeted CAR-NK cells against resistant breast cancer in vivo.

Clinical Implications: Toward a New Era of Breast Cancer Immunotherapy

This study addresses a key clinical challenge: overcoming resistance in ErbB2-positive breast cancer. Resistance mechanisms include ErbB2 alterations, bypass signaling, tumor heterogeneity, and EMT. NK-92/5.28.z cells can target EMT-driven, therapy-resistant cells, offering a promising solution.

CAR-NK cells have several advantages over other immunotherapies. They are off-the-shelf, allowing scalable production. Their dual cytotoxic mechanisms, CAR-driven and innate, reduce the risk of antigen escape. Clinical trials show a favorable safety profile, with no cytokine storms or neurotoxicity. Their ability to attack aggressive tumors further adds to their appeal.

Potential uses include combining CAR-NK cells with current ErbB2 therapies to limit resistance, clearing residual disease, treating advanced or metastatic cancer, and preventing relapse by targeting cancer stem cells. Given the safety shown in trials like CAR2BRAIN, clinical translation to breast cancer appears both feasible and timely.

Challenges and Future Directions

Several challenges remain before CAR-NK therapy can reach its full potential. Technically, systemic delivery must be optimized, as peritumoral injections are unsuitable for metastatic disease. Enhancing NK cell persistence through cytokine support or genetic modification is needed, along with scalable production and clinical standardization.

Biologically, the tumor microenvironment suppresses immune responses, and antigen heterogeneity may lead to escape. Multi-targeted strategies and long-term studies are necessary to assess durability and resistance.

Future work should include orthotopic and metastatic models that better mimic human disease. Combining CAR-NK cells with other therapies may enhance outcomes. Identifying predictive biomarkers and developing next-generation CARs could further improve efficacy in challenging tumor environments.

Conclusion

This study marks a pivotal advancement in breast cancer immunotherapy. Their use of an ErbB2-positive organoid model, combined with CAR-engineered NK cells, provides a powerful preclinical platform for evaluating novel treatments. The NK-92/5.28.z cell line demonstrated potent cytotoxicity against both conventional and aggressive tumor phenotypes, including those resistant to existing therapies.

Given their safety, versatility, and off-the-shelf potential, CAR-NK cells stand out as a promising strategy for treating ErbB2-positive breast cancer, especially in refractory cases. As clinical development continues, these cells may soon offer new hope to patients facing limited therapeutic options. This study also underscores the utility of organoid technology in bridging the gap between in vitro and in vivo research, accelerating the translation of novel therapies from bench to bedside.

Reference

ErbB2/HER2-targeted CAR-NK cells eliminate breast cancer cells in an organoid model that recapitulates tumor progression. Molecular Therapy; 33: 83559-3575; August 06, 2025;DOI: 10.1016/j.ymthe.2025.04.033

 

Disclaimer: This blog post is intended solely for educational and scientific informational purposes. Any mention of therapeutic drug names, including FDA-approved medications, is for the purpose of accurate reporting and discussion of biomedical research and does not constitute medical advice, endorsement, or promotion. Readers should not interpret the content as a recommendation for any specific treatment. Always consult a qualified healthcare professional for medical advice or treatment decisions.

 

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