Glioblastoma multiforme (GBM) remains one of the most formidable and lethal central nervous system malignancies, notorious for its invasive growth patterns and dismal prognosis despite multimodal treatment regimens. Radiotherapy, a cornerstone of GBM management, often falters against an immunosuppressive tumor microenvironment (TME) dominated by TAMs that facilitate tumor proliferation and evade immune clearance. The newly engineered BCG vector responds precisely to this challenge by reprogramming TAMs, effectively disrupting the tumor’s immunosuppressive barrier and augmenting radiation response.

This sophisticated approach draws on the concept of trained immunity, an emerging immunological paradigm whereby innate immune cells exhibit long-lasting functional reprogramming after encountering specific stimuli, akin to adaptive immune memory yet distinct in its mechanisms. The researchers genetically optimized the BCG strain to target and retrain TAMs within glioblastoma niches, which previously have been regarded as difficult to modulate due to their phenotypic plasticity and tumor-supportive functions.

Mechanistically, the engineered BCG delivers pathogen-associated molecular patterns (PAMPs) that engage PRRs (pattern recognition receptors) on TAMs, igniting intracellular signaling cascades including NF-κB and inflammasome activation. These events orchestrate epigenetic remodeling and metabolic rewiring, enriching chromatin accessibility at pro-inflammatory loci and promoting cytokine secretion profiles favorable for anti-tumor immunity. Notably, these reprogrammed TAMs foster an environment conducive to radiotherapy efficacy by increasing tumor cell radiosensitivity and diminishing immunosuppressive checkpoints.

Preclinical validation employed orthotopic murine glioblastoma models, wherein administration of the engineered BCG profoundly altered TAM phenotype from tumor-supportive M2-like states to more pro-inflammatory M1-like profiles. This phenotypic conversion translated to significant tumor regression when BCG treatment was combined with standard-of-care radiation, reducing tumor burden and extending overall survival in treated animals compared to controls receiving radiotherapy alone.

This novel immunotherapeutic strategy taps into the potential of trained innate immunity, which has been once exclusively connected with infections and vaccinations, now repositioned as a formidable antagonistic force against malignancies. The selective triggering of trained immunity circumvents the need for systemic immune activation, thus minimizing off-target inflammatory side effects that often complicate cancer immunotherapy.

Importantly, the study also elucidated the molecular determinants underpinning immune cell reprogramming by the BCG strain. Single-cell transcriptomic analyses unveiled transcriptional signatures indicative of enhanced antigen presentation, chemoattraction of effector lymphocytes, and sustained pro-inflammatory states. These data reinforce the concept that engineered microbes can serve as precise immunomodulators, shaping the TME’s immune landscape to favor therapeutic outcomes.

Glioblastoma’s notorious heterogeneity and adaptive resistance mechanisms make this approach particularly promising, as it leverages an intracellular training of macrophages rather than solely targeting tumor cells directly. By harnessing the immunological plasticity of TAMs, the engineered BCG offers a durable and adaptable immunomodulatory platform capable of synergizing with radiation and potentially other therapeutic modalities such as chemotherapy or immune checkpoint inhibitors.

The implications of this study extend beyond glioblastoma treatment. Engineered microbial vectors representing a versatile class of therapeutic agents raise exciting prospects for modulating trained immunity in diverse solid tumors that exhibit TAM-driven immunosuppression. Furthermore, the concept of tumor-specific innate immune reprogramming could inspire next-generation cancer vaccines or adjuvants designed to tailor immune responses to individual tumor milieus.

Looking forward, translating these findings to clinical settings will necessitate careful evaluation of safety, dosing regimens, and delivery methods to maximize macrophage targeting while avoiding systemic infection risks inherent to live microbial therapies. Advances in synthetic biology and microbial engineering will likely accelerate this process, enabling refined control over immunogenic payloads and tropism.

The convergence of innovative microbiology, immunotherapy, and radiation oncology exemplified by this work epitomizes the cutting-edge frontier of cancer treatment research. By shifting paradigms from directly attacking tumor cells to empowering innate immune senses within the tumor microenvironment, this study offers a compelling blueprint for overcoming resistance and achieving durable remissions in an otherwise devastating disease.

This engineered BCG strategy uniquely exploits the dual capabilities of innate immune memory and microbial engineering to unlock new therapeutic avenues. Unlike classical immune checkpoint blockade that typically targets adaptive immunity, trained immunity harnessed here operates through epigenetic states, providing a complementary and potentially synergistic route to amplify anti-tumor efficacy.

The study’s multidisciplinary approach, spanning virology, immunology, oncology, and genomics, underscores the importance of integrating diverse scientific fields to devise transformative treatment modalities. As each component—from genetic engineering of microbes to characterization of macrophage phenotypes—is finely tuned, the resulting therapeutic synergy offers hope against one of the most aggressive cancer types known to medicine.

In conclusion, the innovative use of a genetically engineered BCG strain to induce trained immunity selectively within tumor-associated macrophages redefines the landscape of glioblastoma therapy. Through a precise immunomodulatory mechanism, this strategy enhances radiotherapy responses, reshapes the immunosuppressive tumor microenvironment, and opens new frontiers for microbial-based cancer treatments. As this technology evolves, it holds the promise not only to improve outcomes for glioblastoma patients but also to revolutionize the broader field of cancer immunotherapy.

Subject of Research: Engineered Bacillus Calmette-Guérin (BCG) therapy inducing trained immunity in tumor-associated macrophages to sensitize glioblastoma to radiotherapy.

Article Title: Engineered BCG selectively triggers trained immunity in tumor-associated macrophages and sensitizes glioblastoma to radiotherapy in mice.

Article References:
Ren, K., Yuan, Z., Lei, L. et al. Engineered BCG selectively triggers trained immunity in tumor-associated macrophages and sensitizes glioblastoma to radiotherapy in mice. Nat Commun (2026). https://doi.org/10.1038/s41467-026-72067-7

Image Credits: AI Generated

One particularly promising modality emerging in recent years is sonodynamic therapy (SDT), which exploits ultrasound waves to activate sonosensitizers preferentially accumulated within tumors. SDT offers superior deep tissue penetration and precise spatiotemporal control compared to traditional photodynamic therapy. However, existing sonosensitizers face substantial limitations. Inorganic-based systems often suffer from poor biodegradability and potential long-term toxicity. Meanwhile, purely organic small molecule sensitizers lack the versatility needed for multifunctional integration and efficient reactive oxygen species (ROS) generation. To surmount these obstacles, Ming Wu and colleagues at the Gongli Hospital of Pudong New Area have pioneered an innovative sonodynamic platform based on covalent organic frameworks (COFs), which are crystalline, porous polymers known for their tunable structures, biocompatibility, and abundant functionalization sites.

Their groundbreaking study reports the synthesis of ferrocene-modified nanoscale COFs (mCOFs) that marry the structural advantages of COFs with the catalytic properties of ferrocene moieties. By reacting microscale COFs with aminoferrocene, the researchers achieved effective nanosizing alongside the integration of Fenton-like catalytic centers. This dual functionality is pivotal: under ultrasonic irradiation, mCOFs generate singlet oxygen (^1O_2), a potent cytotoxic ROS, while the embedded ferrocene units catalyze the conversion of the naturally elevated hydrogen peroxide (H_2O_2) within the tumor microenvironment into highly reactive hydroxyl radicals (·OH). This tandem ROS amplification enables enhanced oxidative stress, resulting in robust tumor cell lethality.

Comprehensive physicochemical characterization confirmed that the mCOFs exhibit optimal particle size, dispersibility in biological media, and crystalline integrity—a foundation critical for reproducible biological activity. Additionally, in vitro assays demonstrated that mCOFs efficiently enter 4T1 breast cancer cells and induce markedly increased intracellular ROS upon ultrasound exposure. These ROS bursts trigger different cell death pathways, including apoptosis and ferroptosis, as evidenced by elevated lipid peroxidation and mitochondrial dysfunction markers. Unlike apoptosis, which is caspase-dependent programmed cell death, ferroptosis is characterized by iron-dependent lipid peroxidation, providing mechanistic synergy through complementary cytotoxic mechanisms.

Beyond direct tumoricidal effects, the mCOF + ultrasound combination stimulated immunogenic cell death (ICD)—a form of apoptosis that heightens anti-tumor immune responses. The hallmark features of ICD, such as the release of damage-associated molecular patterns (DAMPs) like ATP, were significantly upregulated. This, in turn, promoted the maturation and activation of dendritic cells (DCs), critical antigen-presenting cells in orchestrating adaptive immunity. Pro-inflammatory cytokines including interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also elevated, fostering an inflamed microenvironment conducive to immune-mediated tumor clearance.

Moving from cell culture to animal models, the team employed orthotopic breast tumor-bearing mice to evaluate therapeutic efficacy and biodistribution. Intravenous administration of mCOFs achieved high tumor accumulation due to favorable nanoscale dimensions and surface properties, with sonodynamic activation significantly suppressing tumor growth without obvious systemic toxicity. Furthermore, in a clinically relevant bone metastasis model, mCOF treatment attenuated osteolytic lesions, preserving bone volume fraction and mineral density. These results underscore the ability of mCOFs not only to control primary tumors but also to mitigate metastatic spread and bone destruction, which are principal causes of morbidity and mortality.

Immunophenotyping of tumor-infiltrating leukocytes revealed striking increases in mature DCs, helper CD4+ T cells, cytotoxic CD8+ T cells, natural killer (NK) cells, and interferon-gamma (IFN-γ)-producing CD8+ T cells after mCOF + ultrasound treatment. This immune remodeling indicates that the sonodynamic platform effectively reverses tumor immunosuppression and mobilizes both innate and adaptive immune arms to mount a concerted attack against cancer. Such remodeling is critical for durable responses and prevention of metastatic recurrence.

The innovation in this study lies in the precise integration of sonodynamic therapy with Fenton reaction-based chemotherapy and immune modulation via a single nanoscale platform. The ferrocene modification imparts catalytic ROS amplification, overcoming the intrinsic oxidative resistance of tumors, while the COF scaffold ensures structural robustness and biocompatibility. By eliciting ICD alongside ferroptosis and apoptosis, the mCOFs stimulate systemic antitumor immunity—a distinct advantage over conventional therapies that often induce immunologically silent cell death facilitating tumor escape.

This research sets a precedent for the rational design of multifunctional sonosensitizers employing covalent organic frameworks as versatile carriers. The top-down approach to ferrocene incorporation opens avenues for tailoring nanoformulations with synergistic therapeutic mechanisms. Importantly, the successful suppression of both breast cancer progression and its devastating bone metastases highlights the clinical translational potential of mCOFs. Such innovations are urgently needed to address unmet needs in metastatic breast cancer treatment paradigms.

Ming Wu and collaborators emphasize that their findings also reinforce the concept that combining sonodynamic therapy with immunomodulation may overcome the historical limitations of therapies focused solely on primary tumor ablation. This multidimensional strategy disrupts the permissive tumor microenvironment favoring metastasis and immune evasion.

In conclusion, the ferrocene-modified nanoscale covalent organic framework platform represents a leap forward in cancer nanomedicine. It harnesses ultrasound-triggered ROS generation augmented by Fenton catalysis, induces dual apoptosis and ferroptosis pathways, and recalibrates the tumor immune milieu to achieve comprehensive tumor control. Future investigation into clinical translation, pharmacokinetics, and combinatorial regimens with immunotherapy could further enhance its therapeutic impact, potentially revolutionizing the management of metastatic breast cancer and other solid tumors.

Subject of Research: Ferrocene-Modified Nanoscale Covalent Organic Frameworks for Multifunctional Sonodynamic Therapy in Breast Cancer and Bone Metastasis

Article Title: Ferrocene-Modified Nanoscale Covalent Organic Frameworks for Ferroptosis-Based Sonodynamic Therapy Inhibit Breast Cancer and Its Bone Metastasis

News Publication Date: March 23, 2026

References: Published in Cyborg and Bionic Systems

Image Credits: Ming Wu, Gongli Hospital of Pudong New Area

Keywords: Breast cancer, bone metastasis, sonodynamic therapy, covalent organic frameworks, ferrocene, reactive oxygen species, ferroptosis, immunogenic cell death, tumor microenvironment, nanomedicine, oxidative stress, immune modulation