Spleen-Targeted mRNA Vaccine Induces Tumor Regression and Immune Cell Organization in a Liver Cancer Mouse Model
Boosting Antitumor T-Cell Responses by Delivering mRNA to the Spleen
A spleen-targeted neoantigen mRNA vaccine (STNvac) showed tumor regression and improved survival in mouse models of hepatocellular carcinoma (HCC). The researchers analyzed a T-cell subset that increased after vaccination and tertiary lymphoid structures (TLS) at the tumor margin, and described interactions among immune cells involved in the antitumor response. Efficacy was evaluated in mice; human data came from cell culture experiments and analyses of public datasets.
Neoantigen vaccines are designed to present antigens arising from tumor mutations to the immune system so it can recognize cancer cells. In HCC, insufficient numbers of tumor-recognizing T cells and limited persistence of their responses remained a challenge. How might an immune response initiated by delivering mRNA to the spleen, which is rich in antigen-presenting cells (APCs), continue within tumors? This was the question the study examined.
The delivery vehicle was a lipid nanoparticle (LNP) composed of two lipids, DOTMA and DOPE. The researchers combined it with mRNA encoding seven mouse liver cancer neoantigens. They optimized the formulation to increase spleen-selective mRNA expression; the three-dose schedule was used separately to evaluate therapeutic effects.
Complete Tumor Regression in 4 of 7 Mice
The main treatment experiment used an orthotopic HCC mouse model created by implanting Hepa1-6-Luc cancer cells in the liver. Seven mice were assigned to each group, and tumor burden was monitored for eight weeks. The first dose was given seven days after tumor implantation: 10 μg of mRNA intravenously, followed by an additional 5 μg on days 3 and 7 after the first dose. The total dose was 20 μg per mouse.
In the STNvac group, four mice showed complete tumor regression between weeks 4 and 8 of observation. At the end of observation, 6 of 7 mice in the STNvac group were alive, compared with 1 of 7 in the phosphate-buffered saline control group. All seven mice given neoantigen mRNA without a delivery vehicle died; in the group given LNPs carrying control-sequence mRNA, 1 of 7 survived. These results apply to the observation period in this mouse model and provide no basis for interpreting the findings as a cure rate or long-term survival rate in patients.
Single-cell RNA analysis and multiplex immunofluorescence showed an increase after vaccination in CD8 T cells expressing interferon-stimulated gene 15 (ISG15). These cells had cytotoxicity- and activation-associated features. Another change, identified by spatial transcriptomic analysis and tissue staining, was an increase in TLS at the tumor margin. ISG15-positive CD8 T cells were distributed around these structures, where immune cells gather and become organized.
The researchers focused on an interaction between granzyme A (GZMA) from APCs and the receptor F2R on these T cells. When an F2R antagonist was co-administered, T-cell activation and proliferation and the tumor-suppressive effect weakened, while TLS density also decreased. This finding supports the interpretation that the pathway contributes to the vaccine response.
Human Efficacy and Causality in the Mechanism Remain Questions for Further Research
Human evidence came from experiments culturing tumor-infiltrating lymphocytes (TILs) from two surgical patients and from reanalysis of public patient data. Activation markers increased after GZMA stimulation in one patient, but did not increase further in the other. Related signals and spatial arrangements were also observed in human tissue. However, these were not findings from a test of clinical efficacy in patients treated with STNvac.
Questions about the mechanism also remain. Direct validation by selectively depleting or transferring ISG15-positive CD8 T cells could not be performed. It is therefore difficult to conclude that the ISG15 molecule itself acts as a catalyst that strengthens antitumor effects, or to establish that these cells directly induce TLS formation. Further work is also needed to assess the pharmacokinetics, spleen targeting, and safety of intravenously administered LNPs in humans, as well as patient-specific neoantigen prediction and manufacturing feasibility.
The findings and limitations are described in the full Cell Reports Medicine paper. EMOTION_TAG: interesting
The efficacy of neoantigen vaccine for advanced hepatocellular carcinoma (HCC) is limited largely due to insufficient T cell mobilization and activation. Herein, we develop a spleen-targeted neoantigen mRNA vaccine (STNvac) with highly efficient spleen-selective mRNA transfection. Using a three-dose vaccination regimen, STNvac demonstrates remarkable therapeutic efficacy in orthotopic HCC model with a high likelihood of complete tumor regression and significantly improved survival rates (p < 0.0001). Notably, we identify a distinct ISG15
This study provides evidence for assessing both where antigens are delivered in liver cancer vaccine development and how immune cells gather and interact within tumors. In further preclinical development, researchers could compare spleen-targeted formulations while examining not only tumor suppression but also the activity of ISG15-positive CD8 T cells and TLS formation. These measures have not been validated as predictors of treatment response in patients. Moving toward clinical evaluation will require procedures to select and manufacture patient-specific neoantigens, and confirmation of delivery characteristics and safety in humans. The practical value of the current results lies in preclinical evidence that clarifies these development tasks, rather than an established treatment benefit for patients.