Eliminating Ex Vivo Manufacturing: Novel mRNA Nanoparticles Generate CAR-T Cells Directly in Mice

CAR-T therapy typically requires T cells to first be collected from a patient’s blood, genetically modified, expanded, and quality-tested ex vivo, and then reinfused into the body. This process is time-consuming and expensive, and it also limits the scale of treatment. A research team from Xiamen University and other institutions has now proposed another approach: using mRNA nanoparticles to transiently reprogram T cells directly in animals, enabling them to recognize diseased tissue.

The study, published in *Nature Materials*, used polymer–lipid nanoparticles called ERTLNP. After intravenous injection, the functional mRNA carried by the vector was expressed mainly in the spleen and preferentially transfected splenic T lymphocytes. Unlike some existing in vivo CAR-T strategies, it does not require antibodies or other ligands to be attached to the particle surface, nor does it require separate external stimulation of T cells.

The material itself is more than a delivery vehicle. The research team’s mechanistic experiments indicate that ERTLNP may signal through cell-surface IGF-1R and intracellular TM4SF5 into the PI3K/AKT/mTOR pathway, altering T-cell metabolism and promoting proliferation and effector function. The experimentally generated T cells also exhibited relatively fewer exhaustion-associated phenotypes, but these findings are not sufficient to conclude that the same responses would occur in humans.

To test therapeutic applications, the researchers loaded the particles with CAR mRNA targeting fibroblast activation protein, or FAP. After the animals received systemic administration, functional CAR-T cells formed transiently in vivo and subsequently cleared pathologically activated fibroblasts. The paper reported therapeutic effects in pulmonary fibrosis and cancer models; university materials additionally stated that the study also evaluated mouse models of liver fibrosis and pancreatic cancer.

Using mRNA instead of permanent genetic modification may allow CAR expression to diminish over time, providing a reversible safety boundary when targeting molecules such as FAP that may also appear during tissue repair. However, transient expression may also mean that repeated dosing is required; the number of T cells transfected by each injection, whether immune activation can be controlled, and whether the carrier accumulates in different organs will all affect clinical feasibility.

The evidence currently remains limited to preclinical models. The study’s reported low off-target effects have not been validated in human trials, and the regression of fibrosis and control of tumors in animals cannot be directly translated into efficacy in patients. To advance toward clinical use, researchers must also establish reproducible manufacturing and dosing standards, clarify the risks of cytokine release, damage to healthy tissue, and repeated dosing, and demonstrate that this in vivo generation approach can indeed be faster, safer, or more cost-effective than current CAR-T manufacturing processes.