Magnetic nanoparticles engineered T cells inside living mice and guided them into solid tumors, achieving over 90% tumor inhibition where conventional immunotherapy fails.
(Nanowerk Spotlight) Chimeric antigen receptor T-cell therapy, known as CAR-T, has transformed the treatment of blood cancers. The approach involves extracting a patient’s T cells, genetically modifying them in a laboratory to recognize specific tumor markers, then infusing millions of these altered cells back into the body to hunt down cancer. Six CAR-T therapies have received FDA approval since 2017, producing remarkable remissions in patients with leukemias and lymphomas that had resisted all other treatments.
Yet solid tumors, the cancers that kill most people, remain largely impervious. The problem is twofold. First, CAR-T cells struggle to penetrate the dense, fibrous architecture of solid tumors. Second, even when they manage to infiltrate, the tumor microenvironment suppresses their activity, rendering them exhausted and ineffective.
The manufacturing process presents additional hurdles: extracting cells, genetically engineering them over weeks in specialized facilities, and reinfusing them costs hundreds of thousands of dollars and requires infrastructure few hospitals can provide.
Researchers have explored alternatives. Some have attempted to engineer T cells directly inside the body using viral vectors that deliver CAR-encoding genes. Others have tried non-viral nanoparticle delivery systems. While these approaches have shown promise in laboratory animals with blood cancers, none has succeeded in treating solid tumors. The engineered cells still cannot reach or remain active within tumor tissue.
Crucially, this approach requires no genetic modification. Instead, the nanoparticles reprogram T cells by attaching to their surface, bypassing the costly and time-consuming gene-editing steps that define conventional CAR-T manufacturing. These surface-engineered cells can then be physically guided into tumors using an external magnetic field.
The technology, called M-BiNanoAb (magnetic bispecific nano-antibody), consists of iron oxide nanoparticles functionalized with beta-cyclodextrin, a ring-shaped sugar molecule. This surface chemistry allows two types of antibodies to attach through supramolecular interactions with adamantane, a small hydrocarbon molecule linked to each antibody. One antibody targets CD3, a protein found on all T cells. The other targets PDL1 (programmed death-ligand 1), a checkpoint protein commonly overexpressed on cancer cells.
Schematic illustrating the CAR-T-mimicking cells generated by M-BiNanoAb for anti-tumor immunity. (a) Conceptual diagram depicting the mechanism and process of M-BiNanoAb-mediated in vivo T cell binding and engineering. (b) Following injection, M-BiNanoAb instantaneously binds to peripheral blood T cells, thereby generating engineered CAR-T-mimicking cells in situ (I). Guided by an externally applied magnetic field, these M-BiNanoAb-engineered CAR-T-mimicking cells exhibit directed migration and infiltrate the tumor microenvironment (II). Within the tumor niche, the CAR-T-mimicking cells identify and engage with PDL1-overexpressing cancer cells, thereby exerting a potent and prolonged cytotoxic response (III). Ultimately, the lysis of tumor cells leads to the release of tumor antigens, which in turn induce the generation of antigen-specific T cells through epitope spreading, thus amplifying the systemic immune response (IV). (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
The design mimics conventional CAR constructs. In standard CAR-T cells, an extracellular domain recognizes tumor antigens while an intracellular signaling domain activates the T cell upon binding. Here, the anti-PDL1 antibody identifies cancer cells while the anti-CD3 antibody triggers T cell activation. When injected intravenously, the nanoparticles bind to circulating T cells within hours. Flow cytometry analysis showed that approximately 80% of T cells in the bloodstream had bound the nanoparticles four hours after injection in mice.
The magnetic core enables something conventional CAR-T therapy cannot achieve. When researchers placed a small neodymium magnet at the tumor site, T cells carrying nanoparticles migrated toward it. In laboratory migration assays, the magnetic field increased T cell movement by about 22-fold compared to cells without magnetic guidance. Even under conditions simulating blood flow, the engineered cells moved against the current toward the magnetic field.
Tests in tumor-bearing mice demonstrated the therapeutic potential. In the B16-F10 melanoma model, treatment with M-BiNanoAb under magnetic field guidance achieved greater than 90% tumor inhibition. Without the magnetic field, the same nanoparticles produced only approximately 60% inhibition. A combination of separate anti-CD3 and anti-PDL1 nanoparticles achieved only 43% inhibition, indicating that the bispecific design on a single particle is essential.
The researchers also tested the platform in 4T1 breast tumors, which naturally exclude T cells and resist immunotherapy. Under magnetic guidance, M-BiNanoAb treatment extended median survival from 16.5 days to 53 days. Three of ten mice survived beyond 60 days without detectable tumor.
Analysis of tumor-infiltrating lymphocytes revealed why the therapy worked. Magnetically guided T cells showed markers of activation rather than exhaustion. The proportion of exhausted PD1-positive CD8 T cells dropped from about 51% in untreated tumors to roughly 8% in treated tumors. This likely reflects the dual function of the anti-PDL1 antibody: it both targets cancer cells and blocks the immunosuppressive PD1/PDL1 signaling pathway that normally depletes T cell function.
The platform also induced epitope spreading, a phenomenon in which killing tumor cells releases antigens that stimulate immune responses against additional tumor proteins. In mice bearing tumors expressing ovalbumin as a model antigen, treatment increased ovalbumin-specific CD8 T cells by approximately fourfold, even though the nanoparticles targeted PDL1, not ovalbumin.
Treated mice also developed immune memory. Animals that received M-BiNanoAb therapy and then had their tumors surgically removed showed nearly complete protection when rechallenged with fresh tumor cells. Four of nine mice developed no detectable tumors.
The therapy demonstrated a favorable safety profile. Cytokine levels rose transiently, peaking at 24 hours and returning to baseline within 120 hours. Importantly, markers of liver function (AST and ALT) and kidney function (creatinine and blood urea nitrogen) remained comparable to untreated controls throughout the study, with no statistically significant changes.
The approach offers advantages over conventional CAR-T manufacturing. Because it reprograms T cells through surface attachment rather than genetic modification, it eliminates the need for cell extraction, ex vivo culture, and gene editing. The supramolecular chemistry also allows flexibility: different antibodies could target other tumor antigens. The researchers demonstrated this by substituting anti-HER2 antibodies and showing effective killing of HER2-positive breast cancer cells.
Significant questions remain before any clinical application. Magnetic field penetration depth limits which tumors could be treated. The long-term fate of the nanoparticles requires further study. Whether the approach will work in humans, whose tumors are larger and more heterogeneous than those in mice, remains uncertain.
The research opens a new direction for solid tumor immunotherapy, combining in vivo surface engineering with physical guidance to address two problems that have limited progress in the field. Should subsequent studies confirm these results in larger animals and eventually humans, the technology could extend T-cell therapy to cancers that currently lack effective immunotherapeutic options.
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