Ultra-low-dose self-amplifying mRNA vaccine achieves 91% survival in mice bearing HPV16 tumors
Background
Human papillomavirus (HPV) type 16, a major cause of cervical cancer, promotes cell proliferation through the E6 and E7 oncoproteins. Preventive vaccines block infection itself, whereas patients who are already infected need therapeutic vaccines that directly attack tumor cells. Existing E6/E7-targeted therapeutic vaccines have faced barriers to clinical translation because of low immunogenicity and high production costs.
Self-amplifying mRNA (saRNA) is a next-generation platform that replicates within cells to amplify antigen expression. Its ability to substantially reduce the administered dose compared with conventional mRNA has attracted interest for lowering costs and expanding access. However, few studies have systematically evaluated the immune responses and antitumor efficacy of saRNA vaccines targeting HPV tumor antigens.
Key findings
In this study, published in Cancer Immunology, Immunotherapy, Rui Xing and colleagues evaluated JJ-saRNA-HPV01, an saRNA vaccine encoding an HPV16 E6-linker-E7 fusion protein and formulated in lipid nanoparticles (LNPs), in a C57BL/6 mouse model.
When administered therapeutically in the TC-1 tumor model, the vaccine achieved a tumor growth inhibition (TGI) rate of 93.0% at a dose of 0.1 µg. The 1 µg dose achieved a TGI of 95.7%, complete remission, and a 91% survival rate (p < 0.001). The prophylactic vaccination group showed 100% protection following tumor inoculation. In a separate rechallenge experiment, survivors that had become tumor-free after vaccine treatment following tumor inoculation rejected a subsequent tumor challenge without revaccination, confirming the formation of durable E7-specific immune memory.
In the immune-mechanism analysis, intratumoral CD8+ and CD4+ T-cell frequencies both showed an increasing trend in the 1 µg group, but the changes were not statistically significant. The frequency of IFN-γ-positive effector T cells rose markedly (p < 0.001), while PD-1 expression on tumor-infiltrating lymphocytes decreased, indicating a reduction in an exhaustion-associated marker. However, because PD-L1 expression on tumor and myeloid cells was not directly measured, reversal of T-cell exhaustion cannot be established. These findings indicate that CD8+-dependent cytotoxic immunity drives the vaccine’s antitumor effect.
Implications and outlook
JJ-saRNA-HPV01 showed potential to address both key limitations of existing therapeutic vaccines: low immunogenicity and high production costs. The strong antitumor immunity elicited by an ultra-low dose of 0.1 µg opens a path toward large-scale vaccination in resource-limited settings.
The data to date, however, are limited to preclinical mouse studies. Given the complexity of the human immune system, HLA diversity, and differences in the tumor microenvironment, further validation is needed in orthotopic or genetically engineered mouse models, or in humanized mouse models expressing human leukocyte antigens (HLA), to establish the feasibility of clinical application. If the three features—dual preventive and therapeutic efficacy, dose reduction, and long-term immune memory—are also reproduced in clinical settings, this approach could mark a meaningful turning point in strategies for treating HPV-associated malignancies.
BACKGROUND: Human papillomavirus (HPV), particularly high-risk types such as HPV16, is associated with several malignancies, including cervical cancer. Existing therapeutic vaccines targeting HPV oncoproteins E6 and E7 show limited immunogenicity and high production costs. Self-amplifying mRNA (saRNA) vaccines offer a promising alternative by enabling robust antigen expression at low doses. This study evaluated the immunogenicity and antitumor efficacy of a novel saRNA vaccine, JJ-saRNA-HPV01, targeting HPV16 E6/E7 in a preclinical mouse model. METHODS: JJ-saRNA-HPV01, encoding an HPV16 E6-linker-E7 fusion protein, was encapsulated in lipid nanoparticles (LNP). Physicochemical properties (size, PDI, encapsulation efficiency, and zeta potential) were characterized, and in vitro expression was confirmed in 293 T cells by Western blot. Female C57BL/6 mice were immunized intramuscularly with single or double doses (0.1-5 µg). Immune responses were assessed by IFN-γ ELISpot, CD8⁺CD69⁺ T-cell activation, and tumor-infiltrating lymphocyte analysis. Antitumor efficacy was evaluated in TC-1 tumor-bearing mice, with prophylactic and long-term protection tested by tumor challenge and re-challenge. Statistical tests included one-way and two-way ANOVA with multiple comparisons and Kaplan-Meier survival analysis with Mantel-Cox test. RESULTS: JJ-saRNA-HPV01 elicited potent, dose-dependent, E7-specific CD8⁺ T-cell responses in the mouse model. In therapeutic TC-1 models, both 0.1 and 1 µg doses markedly inhibited tumor growth (TGI = 93.0 and 95.7%) and improved survival (p < 0.001), with the 1 µg dose achieving complete regression and 91% survival. Prophylactic vaccination provided 100% protection and cured mice rejected tumor re-challenge, confirming durable E7-specific memory. Mechanistically, vaccination increased intratumoral CD8⁺ infiltration with limited CD4⁺ recruitment, elevated IFN-γ⁺ effector T-cell frequencies (p < 0.001), and reduced PD-1 expression on tumor-infiltrati
HPV-associated cancers impose the greatest disease burden in low- and middle-income countries, yet existing therapeutic vaccines have been difficult to distribute because of their high cost and refrigerated distribution requirements. The dose-sparing property of the saRNA platform could increase the number of people vaccinated per production batch several dozenfold, with potential to help reduce global health disparities. The mechanistic evidence of reduced PD-1 expression on tumor-infiltrating T cells also provides a direct clue for designing combination strategies with immune checkpoint inhibitors. Expanding indications beyond cervical cancer to HPV-associated cancers such as head and neck cancer and anal cancer is another area to explore.