Ultra-low dose self-amplifying mRNA vaccine achieves 91% survival in HPV16 tumor-bearing mice
Background
Human papillomavirus (HPV) type 16, a major cause of cervical cancer, promotes cell proliferation through its oncoproteins E6 and E7. While prophylactic vaccines prevent infection, therapeutic vaccines are needed for patients already infected to directly target tumor cells. Existing E6/E7-targeted therapeutic vaccines have suffered from low immunogenicity and high production costs, hindering clinical translation.
Self-amplifying mRNA (saRNA) is a next-generation platform that replicates within cells, amplifying antigen expression. Compared to conventional mRNA, it allows for significantly reduced doses, making it attractive for cost reduction and improved accessibility. However, few studies have systematically investigated the immune responses and antitumor efficacy of saRNA vaccines targeting HPV tumor antigens.
Key Findings
In a study published in Cancer Immunology, Immunotherapy, Rui Xing et al. evaluated the saRNA vaccine JJ-saRNA-HPV01, encoding an HPV16 E6-linker-E7 fusion protein, encapsulated in lipid nanoparticles (LNP) in a C57BL/6 mouse model.
Therapeutic administration in a TC-1 tumor model resulted in a tumor growth inhibition (TGI) rate of 93.0% at a dose of 0.1 µg. A 1 µg dose achieved a TGI of 95.7% and complete regression, with a 91% survival rate (p < 0.001). Prophylactic vaccination successfully protected against tumor development in 100% of mice, and without re-vaccination, the mice rejected tumor re-challenge, confirming the formation of sustained E7-specific memory immunity.
Analysis of the immune mechanism revealed a significant increase in intratumoral CD8+ T-cell infiltration, while CD4+ T-cell recruitment was limited. The frequency of IFN-γ-positive effector T cells was significantly increased (p < 0.001), and PD-1 expression on tumor-infiltrating lymphocytes was reduced, suggesting an inhibitory effect on T-cell exhaustion. CD8+-dependent cytotoxic immunity is the primary driver of the vaccine's antitumor effect.
Significance and Outlook
JJ-saRNA-HPV01 demonstrates the potential to overcome the key limitations of existing therapeutic vaccines: low immunogenicity and high production costs. The ability to induce a strong antitumor immune response with an ultra-low dose of 0.1 µg opens the door for large-scale vaccination in resource-limited settings.
However, the current data are limited to preclinical mouse studies. Given the complexity of the human immune system, HLA diversity, and differences in the tumor microenvironment, further validation in non-human primate models is essential before clinical translation. If the dual efficacy of prevention and treatment, the dose-sparing advantage, and the formation of long-term immunological memory are replicated in clinical trials, it could represent a significant turning point in the treatment of HPV-related 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-related cancers pose the greatest disease burden in low- and middle-income countries, but existing therapeutic vaccines have been difficult to distribute due to their high cost and cold-chain requirements. The dose-sparing properties of the saRNA platform can increase the number of individuals who can be vaccinated per production batch by a factor of tens, with the potential to reduce global health disparities. Furthermore, the mechanistic evidence of reduced PD-1 expression on tumor-infiltrating T cells provides direct clues for the design of combination strategies with immune checkpoint inhibitors. In addition to cervical cancer, expansion to other HPV-associated cancers, such as head and neck cancer and anal cancer, is also being explored.