Lipid nanoparticles reprogram natural killer cells inside the body to fight cancer

A team of researchers at the Massachusetts Institute of Technology has developed a way to genetically reprogram natural killer cells directly inside living animals, without ever removing the cells from the body. Writing in Nature Biotechnology, Yuang Chen, Julia Monkovic, Haseeb Mughal, Robert Langer, Daniel G. Anderson and colleagues describe a class of ligand-directed lipid nanoparticles that deliver messenger RNA selectively into NK cells, converting them into chimeric antigen receptor-bearing killers capable of destroying B cell cancers, autoreactive T cells and solid tumors in mouse models. The work represents one of the most ambitious demonstrations yet of in vivo cell engineering, a strategy that could in principle replace the costly and logistically complex ex vivo manufacturing processes that currently limit cell therapy to specialized centers.

The core challenge the team faced is one that has long frustrated the field of nonviral cell engineering. Lipid nanoparticles, the same delivery technology behind the leading mRNA COVID-19 vaccines, are remarkably efficient at transfecting liver cells after intravenous injection, but they are far less adept at reaching immune cells circulating in the blood. NK cells in particular are notoriously difficult to transfect with conventional LNPs, and their engineering has typically relied on viral vectors or electroporation performed in the laboratory, both of which add expense, delay and complexity. To overcome this barrier, the MIT group engineered a library of targeted nanoparticles decorated with antibody fragments designed to bind receptors found on the surface of NK cells.

The key innovation lies in the use of engineered biparatopic ligands, antibody-derived binding molecules that engage two distinct epitopes on the same receptor. The researchers conjugated these single-chain variable fragments to the surface of ionizable lipid nanoparticles, creating what they call NK cell-targeted LNPs, or NtLNPs. Among the most effective were particles bearing a biparatopic ligand directed against NKG2D, an activating receptor abundantly expressed on NK cells. Molecular dynamics simulations, run alongside the experimental screening, helped the team understand how the biparatopic design engages more residues at the receptor interface than a single-epitope binder, likely stabilizing the interaction long enough for the particle to be internalized. The multivalent engagement appears to be critical: by gripping the receptor at two sites simultaneously, the ligand exploits the additivity of binding energies to achieve an avidity effect that monovalent fragments cannot match.

The performance figures reported in the paper are striking. Lead NtLNP formulations achieved transfection of up to roughly 80 percent of NK cells in mice, with minimal off-target delivery to other cell types. That level of selectivity and efficiency, achieved through a simple intravenous injection of synthetic particles, approaches what is typically only seen with optimized viral transduction in a laboratory dish. The nanoparticles encapsulate mRNA encoding the CAR construct, and once the particles are taken up by NK cells, the mRNA is translated in the cytoplasm, producing the chimeric antigen receptor protein that traffics to the cell surface. Because mRNA delivery is transient, the approach avoids the permanent genomic integration associated with viral vectors, a feature that may translate into a more controllable and potentially safer safety profile.

To test whether the engineered cells could actually function as therapies, the researchers first turned to a CD19-targeted CAR, the same antigen target used in approved CAR T cell therapies for B cell malignancies. After systemic administration of NtLNPs carrying CD19 CAR mRNA, the generated in vivo CAR NK cells completely depleted circulating B cells in healthy mice, demonstrating that the reprogrammed cells were not merely expressing the receptor but were actively patrolling and killing target cells throughout the vasculature. This experiment established proof of concept that a single injection of synthetic nanoparticles could generate a functional population of CAR NK cells distributed across the animal.

Perhaps the most clinically provocative result came from an autoimmune disease model. The team engineered NK cells in vivo with a CAR targeting CD3, a pan-T cell marker, and administered the particles to mice with autoimmune hepatitis, a T cell-driven inflammatory liver disease. The CD3-targeted CAR NK cells eliminated nearly all autoreactive T cells in the model, dramatically ameliorating the disease. This finding highlights a potential structural advantage of NK cells over CAR T cells for treating T cell-mediated disorders. CAR T cells directed against T cell antigens face the problem of fratricide, in which the engineered T cells kill one another because they carry the target antigen themselves, and they risk wiping out the entire T cell compartment, including protective immunity. NK cells, by contrast, do not express CD3, so they can be safely directed against T cells without destroying themselves, and their more transient lifespan may limit the duration of immunosuppression.

The platform also proved adaptable to solid tumor immunotherapy through an entirely different mechanism. Rather than arming NK cells with a tumor-targeting CAR, the researchers used NtLNPs to deliver mRNA encoding a secreted or membrane-tethered blocker of the inhibitory checkpoint NKG2A. NKG2A is a receptor that, upon engaging its ligand Qa-1b on tumor cells, dampens NK cell cytotoxicity and contributes to immune evasion in the tumor microenvironment. By targeting the checkpoint in vivo, the NtLNP treatment enhanced antitumor efficacy by relieving Qa-1b-mediated immunosuppression, effectively unleashing the NK cells’ natural killing capacity against tumors that had learned to hide from it. This dual capability, both CAR programming and checkpoint modulation within a single nanoparticle platform, underscores the modularity that the authors emphasize as the system’s defining feature.

Safety data accompanying the study address some of the most obvious concerns about repeated systemic dosing of targeted nanoparticles. The researchers profiled serum cytokines at acute time points, monitored body weight longitudinally, and performed blood chemistry analyses of liver and kidney function at both short and long-term intervals after repeated intravenous administration. Histological examination of major organs, including heart, liver, spleen, lung and kidney, showed no overt toxicity, and the team also measured anti-drug antibody titers against the conjugated antibody fragments, evaluating whether repeated dosing generated neutralizing serum activity that could blunt the platform’s effectiveness. These analyses, while conducted in mice, provide an early indication that the approach may be compatible with the repeat dosing regimens that transient mRNA-based therapies would likely require.

Finally, the team extended the work toward clinical relevance by optimizing the NtLNPs for in vivo engineering of human NK cells. In humanized mouse models bearing human hematologic malignancies, the optimized particles generated human CAR NK cells in vivo that drove regression of two distinct xenograft models, including a Raji lymphoma model and a T cell leukemia model. Cross-species structural analyses of the NKG2D receptor interface, comparing human and murine sequences, helped rationalize why the targeting ligands retained activity across species, with conserved residues forming hydrogen bonds, salt bridges and cation-pi interactions at the binding interface. The authors also validated human T cell depletion in the xenograft setting, confirming that the CD3-directed approach behaves as expected in a human immune context.

The broader significance of the study lies in what it suggests about the future architecture of cell therapy. Ex vivo CAR cell manufacturing requires apheresis, viral transduction, cell expansion and quality control, costs that can run to hundreds of thousands of dollars per patient and confine treatment to a handful of academic and commercial centers. In vivo engineering, by contrast, would in principle allow a physician to administer an off-the-shelf injection that converts a patient’s own immune cells into therapeutics at the bedside. The MIT team’s demonstration that NK cells, long considered among the hardest immune cells to transfect, can be programmed at high efficiency with ligand-directed lipid nanoparticles opens a path toward that vision. Considerable work remains before human trials, including dose optimization, biodistribution refinement and the inevitable surprises of human biology, but the study establishes NtLNPs as a credible and modular foundation for the next generation of immunotherapies, one in which the manufacturing plant is the patient’s own bloodstream.

Subject of Research: In vivo engineering of CAR natural killer cells using NK cell-targeted lipid nanoparticles for cancer and autoimmune disease immunotherapy

Article Title: In vivo engineering of CAR natural killer cells for immunotherapy using ligand-directed lipid nanoparticles

Article References: In vivo engineering of CAR natural killer cells for immunotherapy using ligand-directed lipid nanoparticles. (n.d.). https://doi.org/10.1038/s41587-026-03310-1

Image Credits: AI Generated

DOI: 10.1038/s41587-026-03310-1

Keywords: lipid nanoparticles, natural killer cells, CAR cell therapy, in vivo cell engineering, mRNA delivery, cancer immunotherapy, autoimmune hepatitis, NKG2A checkpoint, biparatopic ligands, nanomedicine, gene therapy, Nature Biotechnology