CD55, also known as decay-accelerating factor, has historically been classified as a complement regulatory protein, a guard that prevents the body’s own complement cascade from shredding healthy tissue. It has also been implicated, in T cells, as a co-stimulatory receptor that fine-tunes adaptive immune responses. The new work, led by Lingyu Li, Zhaozhi Li, Yang Liu and colleagues under the supervision of Yufeng Wang and Jianhua Yu, reveals that on natural killer cells CD55 performs a role that is far more fundamental than previously appreciated. Rather than merely assisting activation, CD55 acts as a self-sufficient primary signal initiator, the molecular ignition switch that allows NK cells to launch their cytotoxic program upon first contact with a tumor.

The researchers found that when an NK cell first encounters a tumor, the activating receptor NKG2D engages its ligands on the malignant cell and triggers a signaling cascade that activates the transcription factor p65, a component of the NF-κB family. This NKG2D–p65 axis drives a rapid upregulation of CD55 on the NK cell surface. In other words, the very act of meeting a tumor instructs the killer cell to equip itself with the molecule it needs to kill. This inducible, self-reinforcing architecture ensures that CD55 appears exactly when and where it is most needed, at the immunological synapse where killer and target cells meet.

What happens next is the mechanistic heart of the study. Unlike its role in T cells, CD55 on NK cells directly binds CD97, a receptor that is abundantly expressed on tumor cells, in what immunologists call a trans interaction, meaning the two molecules engage each other across the junction between two different cells. This CD55–CD97 engagement triggers the aggregation of lipid rafts, the cholesterol-rich, ordered microdomains that float within the cell membrane and serve as organizing platforms for signaling machinery. Within these coalescing rafts sits LCK, the Src-family tyrosine kinase that stands at the apex of the lymphocyte activation cascade. By concentrating lipid rafts, CD55 brings LCK molecules together, permitting their phosphorylation and activation, which in turn amplifies the downstream signaling that commands the release of cytotoxic granules.

The technical elegance of this discovery lies in its demonstration that NK cells do not depend on external co-stimulation to fire their killing apparatus. Where T cells typically require multiple reinforcing signals before committing to attack, the CD55–CD97 lipid raft mechanism provides a single, autonomous activation pathway. The researchers confirmed this through careful loss-of-function experiments: NK cells engineered to lack CD55 showed impaired raft aggregation, diminished LCK activation and weakened cytotoxicity, and these defects could be traced specifically to the raft–kinase axis rather than to CD55’s classical complement-regulating duties. Methyl-beta-cyclodextrin disruption of lipid rafts abrogated the activation induced by CD55 agonists, and the functional defects in CD55-deficient NK cells proved independent of the complement pathway altogether, underscoring that this is a signaling role, not a complement role.

The story darkens when the investigators followed NK cells into the tumor microenvironment. Upon prolonged exposure to tumor cells, CD55 expression on the NK cell surface progressively declines, tracking closely with the well-known downregulation of NKG2D that occurs under chronic stimulation. This erosion of CD55 is not a benign byproduct of exhaustion. Within the tumor microenvironment, the loss of CD55 causally impairs NK cell function, collapsing the raft–LCK signaling platform that the cells depend on and leaving them unable to mount effective attacks. The very chronicity of tumor exposure, which initially instructs NK cells to upregulate CD55, ultimately strips them of the molecule and with it their killer instinct.

To test whether this biology matters in human disease, the team turned to single-cell RNA sequencing data from a remarkable breadth of cancers, including nasopharyngeal carcinoma, melanoma, lung cancer, breast cancer, head and neck squamous cell carcinoma, hepatocellular carcinoma, renal cancer, colorectal cancer and pancreatic ductal adenocarcinoma, drawing on datasets from the Human Tumor Atlas Network and numerous public repositories. The analysis revealed a sobering clinical correlation: in cancer patients, low CD55 expression in tumor-infiltrating NK cells is associated with poor clinical outcomes. CD55 thus emerges not only as a mechanistic linchpin but as a potential biomarker, a molecular gauge of whether a patient’s innate immune arsenal remains armed or has gone quiet.

The most therapeutically consequential finding, however, is that this dysfunctional state is reversible. When the researchers restored CD55 expression in both conventional NK cells and chimeric antigen receptor-engineered NK cells, the effects were striking. Restored CD55 augmented LCK signaling, enhanced effector function and persistence, and improved antitumor efficacy in vivo. Engineered NK cells fortified with sustained CD55 expression proved more lethal against tumors and survived longer within the tumor microenvironment, addressing two of the most stubborn limitations of NK cell immunotherapy: inadequate persistence and functional anergy after adoptive transfer. In mouse models and in the NK92 cell line used clinically, enforced CD55 expression translated into measurably better tumor control.

For the rapidly expanding field of NK cell-based cancer immunotherapy, these findings arrive at a critical moment. CAR-NK therapies have generated enormous enthusiasm because, unlike CAR-T cells, they carry a lower risk of graft-versus-host disease and cytokine storms, and they can be derived from off-the-shelf cell sources. Yet clinical results in solid tumors have lagged behind the promise, precisely because transferred NK cells dysfunction rapidly after entering tumor tissue. The CD55 discovery provides both an explanation and a solution: by engineering CD55 expression into therapeutic NK products, or by finding pharmacological means to preserve it, cell therapists may be able to keep the raft–LCK ignition switch flipped on throughout the cell’s journey into and within the tumor.

Beyond its immediate therapeutic implications, the study reshapes fundamental understanding of how innate immunity is wired. It reveals that NK cells possess an autonomous activation circuit in which tumor recognition, through NKG2D and p65, induces a membrane organizer that then amplifies signaling through lipid raft condensation and LCK activation. It also adds CD55 and CD97 to the growing roster of ligand–receptor pairs whose trans interactions at the immune synapse determine the outcome of encounters between immune cells and cancer. And it frames NK cell dysfunction not as an irreversible slide into exhaustion but as a defined, mechanistically understood state, one whose molecular signature, CD55 loss, can in principle be measured, monitored and corrected. As immunotherapy continues its migration from blood cancers toward solid tumors, the humble complement regulator once known simply as decay-accelerating factor may prove to be one of the most important switches in the killer cell’s arsenal, and flipping it back on could mark a turning point in the effort to make natural killer cells the reliable cancer weapons they have always promised to be.

Subject of Research: The role of the membrane protein CD55 in organizing lipid raft–LCK signaling that drives natural killer cell antitumor immunity.

Article Title: CD55 organizes lipid raft-LCK signaling to potentiate NK-cell antitumor immunity

Article References: Li, L., Li, Z., Liu, Y., Fan, W., Lei, Y., Tian, L., Chen, L., Qu, Z., Shi, Y., Yu, J., & Wang, Y. (2026). CD55 organizes lipid raft-LCK signaling to potentiate NK-cell antitumor immunity. Cell Research. https://doi.org/10.1038/s41422-026-01288-8

Image Credits: AI Generated

DOI: 10.1038/s41422-026-01288-8

Keywords: CD55, natural killer cells, LCK kinase, lipid rafts, NKG2D, tumor microenvironment, CAR-NK cells, immunotherapy, CD97, antitumor immunity, organizes, lipid

Immunotherapy, especially CAR-T cell therapy, has revolutionized treatments for blood cancers like leukemia and lymphoma by genetically modifying patients’ T cells to recognize and attack cancer cells. However, extending these successes to solid tumors has been challenging due to the complex microenvironment and heterogeneity of these cancers. Solid tumors develop dense stromal barriers that immune cells struggle to penetrate, and they frequently display diverse antigenic profiles that allow malignant cells to evade immune detection. The structural sophistication of these tumors, coupled with their immune evasion strategies, has posed formidable obstacles for conventional CAR-T therapies.

Unlike CAR-T cells, engineered CAR-NKT cells leverage the innate tumor-homing properties of NKT cells, enabling them to traverse the physical and immunosuppressive barriers that characterize solid tumors. NKT cells uniquely combine features of both innate and adaptive immunity, allowing them to rapidly respond to tumor antigens and secrete a variety of cytokines that modulate the tumor microenvironment. This dual functionality encourages the destruction of cancer cells while simultaneously dismantling the immunosuppressive shield typically maintained by regulatory cells within the tumor milieu, thereby amplifying the overall immune assault on cancer.

The UCLA study undertook a rigorous comparison of four distinct CAR designs engineered into human NKT cells. Each CAR carries a targeting domain specific to mesothelin, a surface protein highly expressed in several solid tumors, including ovarian, pancreatic, lung, and breast cancers. The four CAR constructs varied primarily in their intracellular signaling and co-stimulatory domains: one featured CD28, another 4-1BB, the third incorporated both CD28 and 4-1BB, and the fourth employed NKG2D and 2B4 costimulatory motifs. These variations influence T cell activation, expansion, cytokine production, and longevity — all critical factors in the therapeutic efficacy of CAR-based immunotherapies.

The team first validated the cytotoxic capabilities of each CAR-NKT variant in vitro by exposing these engineered cells to tumor cells derived from multiple solid cancer types. They meticulously quantified tumor cell lysis, cytokine profiles, and the ability of the engineered NKT cells to persist over time. This extensive laboratory characterization revealed distinct performance profiles aligned with the signaling domains present in each CAR construct, underscoring how molecular engineering of CARs dictates both the intensity and durability of anti-tumor responses.

Following promising in vitro results, the researchers advanced to in vivo models, employing ovarian cancer mouse models to assess therapeutic outcomes. Here, they tracked tumor regression, survival outcomes, and biodistribution of the infused CAR-NKT cells within the animals. Notably, the 4-1BB-containing CAR design emerged as the leading candidate, demonstrating sustained anti-tumor activity coupled with prolonged cellular persistence. This construct outperformed its counterparts by maintaining a functional presence within tumors and secondary lymphoid tissues, translating into significantly improved survival metrics in treated mice.

The superior performance of the 4-1BB costimulatory domain aligns with previous findings in T cell-based therapies where 4-1BB signaling enhances cell survival and promotes a memory-like phenotype. This attribute is especially critical for solid tumor immunotherapy, where continuous immune surveillance and prolonged effector function are required to prevent tumor relapse and overcome immune evasion tactics. The study’s findings strongly suggest that optimizing intracellular signaling domains within CAR-NKT cells can tailor their function for maximal therapeutic benefit.

Importantly, the investigation also addressed safety concerns that often shadow novel cellular therapies. The engineered CAR-NKT cells did not induce off-target toxicity, displayed no signs of graft-versus-host disease (a dangerous immunological reaction common in allogeneic cell therapies), and showed no aberrant clonal expansion, alleviating fears of potential malignancies resulting from uncontrolled proliferation. These safety profiles bolster the clinical feasibility of using CAR-NKT cells as an off-the-shelf, allogeneic immunotherapy product.

This off-the-shelf capability distinguishes CAR-NKT therapy from conventional autologous CAR-T cell treatments, which require harvesting, engineering, and expanding each patient’s own T cells— a process that is time-consuming, expensive, and logistically complex. In contrast, CAR-NKT cells can be mass-produced from donated blood stem cells, cryopreserved, and distributed for immediate use. This paradigm shift could democratize access to advanced immunotherapies, dramatically reducing treatment delays and improving patient outcomes, especially for aggressive solid tumors needing urgent intervention.

The researchers have already published compelling preclinical evidence demonstrating the efficacy of CAR-NKT cells against multiple solid tumors beyond ovarian cancer, including pancreatic and triple-negative breast cancers, two notoriously challenging malignancies to treat. These findings collectively highlight the broad applicability and versatility of CAR-NKT cells across diverse tumor types, expanding the horizon of immunotherapy beyond hematologic cancers.

Dr. Lili Yang, the study’s senior author and a prominent figure in immunology and regenerative medicine at UCLA, emphasized the importance of this work. By systematically dissecting the functional differences among CAR designs in NKT cells, the study provides a critical roadmap for future clinical translation. It empowers scientists and clinicians with concrete data to select CAR configurations that balance immediate cytotoxicity and long-term immune memory, essential for sustained therapeutic success in solid tumor oncology.

As the field moves towards clinical trials, these insights lay the groundwork for a new generation of cellular immunotherapies that combine biological precision with manufacturing scalability. With continued validation, CAR-NKT cells stand poised to become a transformative weapon in the fight against cancer, potentially surmounting challenges that have long confined CAR-based therapies to blood cancers and revolutionizing the treatment landscape for solid tumors worldwide.

This research exemplifies the power of engineering biology at the molecular level to fine-tune immune interventions, combining the inherent tumor-penetrating capacity of NKT cells with tailored CAR signaling domains to create smart, potent cellular therapies. Such innovations reflect a broader trend in cancer immunotherapy towards harnessing the nuances of immune cell biology for optimized design and delivery — paving the way for more effective, safer, and widely accessible cancer treatments.

Subject of Research:
CAR-NKT Cell Therapy Design for Solid Tumor Immunotherapy

Article Title:
Engineering Optimal Chimeric Antigen Receptor Constructs for Allogeneic NKT Cell-Based Solid Tumor Immunotherapy

News Publication Date:
Not specified in the source content

Web References:
https://stemcell.ucla.edu/member-directory/lili-yang-phd
https://stemcell.ucla.edu/
https://www.uclahealth.org/cancer
https://newsroom.ucla.edu/releases/immunotherapy-car-nkt-pancreatic-cancer-ucla
https://newsroom.ucla.edu/releases/ucla-scientists-develop-one-product-fits-all-immunotherapy-breast-cancer
https://newsroom.ucla.edu/stories/immunotherapy-ovarian-cancer-ucla-scientists-develop
https://ashpublications.org/bloodict/article/2/1/100025/557344/Engineering-optimal-CAR-constructs-for-allogeneic

References:
Yanruide Li, Yichen Zhu, Tyler Halladay, Xinyuan Shen, Youcheng Yang, Zhe Li, Enbo Zhu, Yuning Chen, Jie Huang, and Lili Yang. “Engineering optimal CAR constructs for allogeneic invariant natural killer T cell therapy.” Blood Immunology & Cellular Therapy.

Image Credits:
UCLA Broad Stem Cell Research Center

Keywords:
Immunotherapy, Cancer Immunotherapy, Cancer, Cancer Cells, CAR-NKT Cells, Solid Tumors, Chimeric Antigen Receptors, 4-1BB Costimulatory Domain, Mesothelin Targeting, Cellular Therapy, Off-the-Shelf Immunotherapy, Tumor Microenvironment

Cancer remains one of the leading causes of mortality worldwide, with solid tumors posing a significant challenge due to their evasive tactics against the immune system. The findings of this study underscore the critical need for innovative strategies to dismantle the immune evasion mechanisms employed by malignant cells. The potential of NK cells, known for their rapid and robust anti-tumor responses, offers a beacon of hope. However, their effectiveness is often compromised by tumors that intricately manipulate immune modulators such as IL-18 to shield themselves from immune detection.

IL-18, initially synthesized as an inactive precursor known as pro-IL-18, undergoes a pivotal transformation through the action of caspase-1 to yield its mature and biologically active form. Mature IL-18 plays a crucial role in stimulating immune cells, particularly enhancing their ability to combat tumor growth. Traditionally, the secretion of mature IL-18 has been thwarted by its decoy receptor, IL-18 binding protein (IL-18BP), creating a significant barrier for effective anti-tumor immunity. However, recent findings have shifted the paradigm regarding IL-18’s functionalities and its production within tumor cells.

The researchers concentrated their efforts on uncovering the dynamics of IL-18 within the tumor microenvironment, leading to the discovery of a novel short form of IL-18 produced via caspase-3 cleavage. Unlike its conventional counterpart, this short variant does not exit the tumor cells but relocates to the nucleus, where it initiates critical signaling cascades that enhance the anti-tumor activity of NK cells. This atypical pathway illustrates a sophisticated method by which tumor cells can utilize existing molecular machinery to engage immune responses, challenging long-held beliefs about the tumoral manipulation of immune modulation.

The study’s implications are particularly pronounced in the context of colorectal cancer, where researchers noted a striking inverse relationship between the levels of short IL-18 and tumor progression in clinical specimens. This discovery suggests that short IL-18 could serve as a crucial biomarker for tumor aggressiveness, while also acting as a promoter of NK cell-mediated anti-tumor immunity. By harnessing the innate potential of NK cells, the short form of IL-18 could be integral in reshaping the immunological landscape of tumors.

As emphasized by Professor MENG, these findings revolutionize the understanding of IL-18, illuminating its multifaceted roles within the immune system and its unexpected contribution to enhancing NK cell functionality. The revelation that tumor-derived IL-18 can activate immune responses via unconventional pathways invites further exploration into its therapeutic potential. The researchers advocate for the development of targeted immunotherapies that exploit the newfound properties of short IL-18, thus complementing existing treatment modalities and ultimately improving patient outcomes.

Aside from their tumor-suppressing actions, NK cells are recognized for their low toxicity levels, making them particularly appealing as therapeutic agents in cancer treatment. The ability to stimulate NK cells through the modulation of IL-18 provides a strategic advantage in cancer therapies aimed at restoring immune surveillance without causing excessive damage to healthy tissues. Following this study, there lies an exciting frontier in designing targeted therapies that can effectively restore or enhance NK cell activity in the presence of malignancy.

In summary, the groundbreaking findings from the study conducted by Professor MENG and Professor LIU highlight a significant shift in the understanding of IL-18’s role in cancer therapy. The short form of IL-18 acts as a potent activator of NK cells, revealing a new mechanism through which tumors can manipulate the immune system. The promise of developing novel immunotherapeutic strategies based on these insights has the potential to transform the landscape of cancer treatment and pave the way for enhanced patient survival and quality of life.

As the implications of their study garner attention, it is imperative for the scientific community to delve deeper into the molecular mechanisms governing the interaction between IL-18 and NK cells. Future research endeavors could expand on these findings, potentially leading to the exploration of other cancer types and the development of synergistic treatments that leverage the immune system more effectively against tumors. This revolutionary discovery not only enhances the fundamental knowledge of cancer biology but also sets a pivotal stage for new therapeutic approaches that could change the course of cancer immunotherapy as we know it.

In conclusion, Professor MENG and Professor LIU have illuminated a unique mechanism whereby tumors utilize a short form of IL-18 to engage and activate NK cells in the fight against cancer. The potential for developing therapies that harness these findings is vast, and with further research, the dream of utilizing the body’s immune system to combat malignancies more effectively may soon become a reality.

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Subject of Research: Mechanism of IL-18 in NK cell activation against tumors
Article Title: Short IL-18 generated by caspase-3 cleavage mobilizes NK cells to suppress tumor growth
News Publication Date: 31-Jan-2025
Web References: https://www.nature.com/articles/s41590-024-02074-7
References: [Not Provided]
Image Credits: [Not Provided]
Keywords: Cancer immunotherapy, IL-18, Natural killer cells, Tumor immune evasion, Colorectal cancer, Immune modulation, Therapeutic strategies, Cancer treatment.