Overcoming the limits of mRNA cancer vaccines… CpG oligonucleotides enhance T-cell immunity 10-fold
Background
Vaccine platforms loading messenger RNA (mRNA) into Lipid Nanoparticles (LNP) proved their utility during the COVID-19 pandemic. While inducing neutralizing antibodies was sufficient for preventing infectious diseases, cancer vaccines, which must directly attack tumor tissue, require a different type of immune response. Eliminating tumor cells necessitates powerful cellular immunity, including cytotoxic T cells.
Challenges have been consistently raised that current standard mRNA-LNP formulations struggle to induce sufficient T-cell responses to suppress tumors. While various attempts have been made in research to combine different adjuvants to boost T-cell responses, systematic data directly comparing multiple adjuvants under identical conditions has been lacking. There was no established standard for which adjuvant provides optimal efficacy when combined with LNP formulations.
Key Findings
To fill this gap, researchers conducted a screening to evaluate the efficacy of 15 selected adjuvants side-by-side. Among the formulations analyzed, the one combined with Class B CpG oligodeoxynucleotides (CpG ODN) most prominently enhanced T-cell induction and anti-tumor effects in mouse models. This immune-enhancing response occurred via the Interleukin-12 (IL-12) signaling pathway in the body.
Notably, the vaccine supplemented with Class B CpG ODN elicited a more potent T-cell response than mRNA-LNP administered at a 10-fold higher dose without an adjuvant. This demonstrates superiority in safety profiles by inducing a higher immune response while avoiding adverse reactions associated with high-dose administration.
A fascinating aspect was the change in transmission efficiency. Upon adding Class B CpG ODN, a paradoxical phenomenon was observed where cellular LNP uptake and antigen expression levels actually decreased. Mechanistic tracking confirmed that this was due to the negatively charged CpG ODN adsorbing onto the LNP surface, thereby altering the physicochemical surface characteristics of the nanoparticles. Despite the reduction in antigen expression, the powerful co-stimulatory signals induced in the local immune microenvironment drove T-cell activation, ultimately enhancing anti-cancer efficacy.
Significance and Outlook
These results demonstrate that T-cell responses in mRNA cancer vaccines can be enhanced by simply adding Class B CpG ODN to existing formulations without additional structural modification. This approach is considered a safe pathway to maximize anti-tumor therapeutic efficacy while reducing the vaccine antigen dose to one-tenth of the standard level.
At the same time, the study revealed a new variable to consider in formulation design by identifying that interactions between adjuvants and LNPs can change the characteristics of the drug carrier. Further research is needed on composite nanoparticle fabrication processes to prevent or reverse the decrease in delivery efficiency caused by adjuvant adsorption. The researchers plan follow-up studies to verify whether the immune mechanisms confirmed in mouse models function identically in primates and humans.
mRNA-lipid nanoparticle (LNP) vaccines can elicit robust T cell responses; however, these responses remain insufficient, particularly in the context of cancer vaccine therapy. Although several types of adjuvants reportedly enhance T cell responses induced by mRNA-LNP vaccines, few comprehensive side-by-side comparisons exist, and it remains unclear which adjuvants are most suitable. Herein, we screened 15 adjuvants. The addition of class B CpG oligodeoxynucleotides (ODNs) markedly augmented T cell induction in an interleukin-12-dependent manner and promoted the antitumor effects of mRNA-LNP vaccines in mice. Class B CpG ODN-adjuvanted mRNA-LNP vaccines induced more potent T cell responses than the mRNA-LNP vaccine administered at a 10-fold higher dose, while exhibiting a more favorable safety profile. However, this approach also reduced the cellular uptake of mRNA-LNPs and antigen expression. As a possible mechanism underlying this reduced delivery efficiency, we found that class B CpG ODNs adsorbed onto LNPs and altered their particle characteristics. These findings demonstrate that supplementation with class B CpG ODN is a simple, safe, and readily implementable approach for enhancing mRNA-LNP vaccine-induced T cell responses. This study also highlights that adding auxiliary components to mRNA-LNPs can potentially affect the performance of LNPs as delivery carriers.
This research provides an immediate solution for the development of mRNA cancer vaccines, which have faced difficulties entering clinical trials due to toxicity risks from high-dose administration. This is because T-cell induction responses can be significantly improved through a simple formulation change—adding Class B CpG ODN to the existing vaccine manufacturing process.
There is also an economic advantage, as the use of active pharmaceutical ingredients can be reduced tenfold while achieving equal or greater therapeutic effects. If optimization processes for buffer composition or mixing ratios are established to minimize the reduction in antigen expression caused by adsorption onto LNP surfaces, this is expected to rapidly transition into a clinical formulation that enhances the efficacy of personalized neoantigen cancer vaccines.