mRNA Vaccine Paired With Radiotherapy Shrinks HER2-Positive Lung Tumors in Mice

A new preclinical study reports that an mRNA vaccine delivered in lipid nanoparticles, when paired with radiotherapy, dramatically suppresses tumors in a mouse model of HER2-overexpressing lung cancer. The work, published in Bioengineering & Translational Medicine, offers the first evidence that this particular combination can remodel the immune landscape of HER2-positive non-small cell lung cancer (NSCLC), a subtype that currently has few good treatment options and a notoriously poor prognosis.

HER2, a transmembrane receptor tyrosine kinase belonging to the EGFR family, is best known as a driver of breast and gastric cancers, but it is also overexpressed in roughly 7.7 to 23 percent of NSCLC patients. These tumors tend to be aggressive and respond poorly to chemotherapy and conventional targeted agents. Antibody-drug conjugates such as trastuzumab deruxtecan have shown promise, yet they are currently recommended only for HER2-mutant disease, and the DESTINY-Lung01 trial documented substantial grade 3 or higher toxicity and treatment-related deaths in HER2-overexpressing patients. The research team, led by investigators affiliated with Hebei Medical University, set out to fill this gap with a vaccine strategy that recruits the patient’s own immune system rather than relying on systemic drug exposure.

The vaccine itself is a classic product of the post-COVID mRNA era. The researchers synthesized mRNA encoding the human HER2 extracellular domain through in vitro transcription, capping, and polyadenylation, then encapsulated it in lipid nanoparticles built on the well-characterized MC3 ionizable lipid formulation, mixed at a molar ratio of DLin-MC3-DMA, DSPC, cholesterol, and DMG-PEG2000 of 50:10:38.5:1.5. Using a microfluidic device, they produced particles with a median diameter of about 71 nanometers, a polydispersity index of just 0.072, and an encapsulation efficiency of roughly 80 percent. Cryo-electron microscopy showed uniform, spherical particles with dense mRNA cores. Once injected intramuscularly, the nanoparticles deliver their cargo to dendritic cells and other host cells, where the HER2 protein is translated, processed by the proteasome, and presented on both MHC class I and class II molecules, priming cytotoxic T cells and antibody production against what is normally a self-antigen.

Immunogenicity was robust. In both BALB/c and C57BL/6 mice, three doses of the vaccine drove high serum titers of HER2-specific antibodies, and booster immunization pushed titers progressively higher over time. Crucially, the antibody response worked across two different MHC backgrounds, hinting that the antigen design may generalize beyond a single genetic context. Safety testing at the day 70 endpoint showed no pathological changes in heart, liver, lung, or spleen on histology, and complete blood counts, liver enzymes, renal markers, and cardiac enzymes all remained within normal ranges. The only notable finding was reduced spleen weight in vaccinated mice, which the authors attribute to relief of tumor-driven compensatory splenic enlargement rather than toxicity.

To test efficacy, the team engineered a Lewis lung carcinoma cell line stably overexpressing human HER2 using a transposon system, confirming expression levels that fell between the HER2-high breast cancer line SKBR3 and the moderate expresser A549, mirroring the clinical spectrum seen in NSCLC patients. In a prophylactic setting, mice vaccinated before tumor challenge showed significantly slower tumor growth from day 4 onward, and the addition of radiotherapy, delivered as three 8-Gy fractions totaling 24 Gy from a clinical linear accelerator, produced the smallest tumors of any group throughout the 24-day observation window. A striking inverse correlation emerged between antibody titer and final tumor volume, with a Pearson coefficient of -0.889, suggesting the humoral response tracks closely with tumor control.

The therapeutic arm of the study was arguably more clinically relevant. When vaccination began only after tumors were established, with radiotherapy administered on day 14, the combination again outperformed either modality alone, with significantly smaller tumor volumes from day 3 onward and the greatest reductions in both tumor weight and proliferative Ki67 staining. Splenic T lymphocytes from combination-treated mice showed the highest cytotoxic killing of HER2-LLC cells in co-culture assays. Immunohistochemistry confirmed that both HER2 expression and proliferation markers dropped most steeply in the combination group, consistent with the vaccine sensitizing tumors to radiation.

Flow cytometry revealed the mechanistic story underneath these outcomes. Within tumors, the combination therapy increased CD8-positive T cell infiltration beyond either monotherapy and raised the CD8-to-CD4 ratio significantly. Macrophages shifted decisively toward the antitumor M1 phenotype: the M1-to-M2 ratio rose twentyfold with the vaccine alone and thirtyfold with the combination, indicating that radiation amplifies a vaccine-driven reprogramming of the myeloid compartment. NK cells and B cells also expanded, while immunosuppressive regulatory T cells declined. In the spleen, the same pattern held, accompanied by elevated secretion of IFN-gamma, TNF-alpha, IL-2, and IL-4, painting a picture of coordinated systemic Th1-dominant activation with humoral support.

One of the most intriguing findings concerns T cell differentiation. The combination regimen reduced the fraction of CD44-negative CD62L-negative double-negative T cells, a short-lived terminally differentiated subset, while boosting CD8-positive effector memory cells and granzyme B-expressing cytotoxic cells. The authors interpret this as radiation-induced bystander activation at work: irradiated tumor cells undergo immunogenic cell death, releasing damage-associated molecular patterns that redirect quiescent T cells away from transient effector fates and toward durable, memory-like phenotypes with sustained killing capacity. If this holds in humans, the combination might not only shrink existing tumors but seed long-term immune memory against recurrence.

The authors are candid about the limitations of their model. Human HER2 is a xenogeneic antigen in mice, lacking a normal-tissue homolog, which likely inflates the apparent immunogenicity and prevents meaningful assessment of autoimmune risk, a critical concern for any self-antigen-targeted vaccine. The engineered cell line cannot reproduce the heterogeneity of HER2 expression in human tumors, all experiments used male mice to avoid hormonal confounders, and safety was assessed only at a single terminal time point. The team proposes follow-up work in HER2-transgenic or humanized models, dynamic toxicity monitoring, T cell depletion and antibody transfer experiments, epitope mapping, and combination studies with immune checkpoint inhibitors.

Even with those caveats, the study stakes out an important translational position. Only a handful of LNP-based mRNA vaccines have reached clinical testing in lung cancer, and none have specifically targeted HER2-overexpressing patients. Earlier mRNA approaches, such as the five-antigen vaccine BI 1361849 combined with radiotherapy in stage IV NSCLC, demonstrated tolerability and immune activation but did not focus on this molecular subtype. By showing that a single-antigen HER2 mRNA-LNP vaccine can both prevent tumor establishment and radiosensitize established disease, the researchers provide a preclinical rationale for a radio-immunotherapy strategy aimed at one of the most refractory corners of lung oncology, where the flexibility of the mRNA platform could eventually support personalized antigen selection and rapid clinical iteration.

Subject of Research: Combined HER2-targeted mRNA-LNP vaccine and radiotherapy immunotherapy for HER2-overexpressing non-small cell lung cancer in mice

Article Title: Combined HER2‐targeted mRNA‐LNP vaccine and radiotherapy suppress Lewis lung carcinoma growth in mice: Efficacy and mechanistic insights

Article References: Wang, S., Jing, S., Zou, S., Zhang, Y., Ge, M., Gao, K., Li, X., Zhao, L., & Wang, J. (2026). Combined HER2 ‐targeted mRNA ‐ LNP vaccine and radiotherapy suppress Lewis lung carcinoma growth in mice: Efficacy and mechanistic insights. Bioengineering & Translational Medicine, 11(5), Article e70160. https://doi.org/10.1002/btm2.70160

Image Credits: AI Generated

DOI: 10.1002/btm2.70160

Keywords: mRNA vaccine, lipid nanoparticles, HER2, non-small cell lung cancer, radiotherapy, radio-immunotherapy, CD8 T cells, M1 macrophage polarization, tumor microenvironment, Lewis lung carcinoma, immunogenic cell death, preclinical study