Messenger RNA-based Vaccines With Dual Activity Induce Balanced TLR-7 Dependent Adaptive Immune Responses and Provide Antitumor Activity

Abstract

Direct vaccination with messenger RNA (mRNA) molecules encoding tumor-associated antigens is a novel and promising approach in cancer immunotherapy. The main advantage of using mRNA for vaccination is that the same molecule not only provides an antigen source for adaptive immunity, but can simultaneously bind to pattern recognition receptors, thus stimulating innate immunity. However, achieving both features remains challenging, as the complexation of mRNA required for immune-stimulating activity may inhibit its translatability. In this study, we present a new and more effective vaccine design: a two-component mRNA-based tumor vaccine that supports both: antigen expression and immune stimulation, mediated by Toll like receptor 7 (TLR7). The two-component mRNA vaccines, containing free and protamine-complexed mRNA, induce balanced adaptive immune responses providing humoral as well as T cell mediated immunity. This balanced immune response is based on the induction of antigen-specific CD4(+) T helper cells and cytotoxic CD8(+) T cells. Once activated, these CD4(+) and CD8(+) T cells secrete a wide set of cytokines, which drive a TH1 response. Immunization with the two-component vaccines induces sustained memory responses, mediated by antigen-specific memory T cells. Moreover, treatment of mice with the two-component mRNA vaccine mediates a strong antitumor response against OVA-expressing tumor cells, not only in a prophylactic but also in a therapeutic setting. In conclusion, two-component mRNA vaccines with self-adjuvanting activity induce balanced adaptive immune responses and mediate sustained antitumor activity.

Induction of an IFN-Mediated Antiviral Response by a Self-Amplifying RNA Vaccine: Implications for Vaccine Design

“…4E) from TLR7 rsq1 mice revealed the central role of TLR7 as a sensor of SAM in immune cells. These findings are in agreement with previous reports for an mRNA-based tumor vaccine in which in vivo immune stimulation was TLR7 dependent (37). In addition, the cytoplasmic RLRs, RIG-I and MDA5, which are the key mediators of foreign nucleic acid sensing in nonimmune cells, were involved in SAM vaccine recognition, as demonstrated using RGI-I, MDA5, and MAVS KO mice.…”

Selective uptake of naked vaccine RNA by dendritic cells is driven by macropinocytosis and abrogated upon DC maturation

“…8,9 Feasibility and safety of vaccination protocols based on intradermal administration of naked RNA have been shown in preclinical and clinical settings and partial protection from tumor challenge has been achieved in mice. 10,11 However, at present, neither in animals nor in men, systemic immune responses let alone therapeutic effects were unequivocally demonstrated. It is assumed that rapid degradation by ubiquitous RNAses constraining pharmacologically efficient dosing of unprotected RNA contributes to the still suboptimal clinical effects.…”

Evading innate immunity in nonviral mRNA delivery: don’t shoot the messenger

“…Although this naturally occurring protein is demonstrated to protect the mRNA from degradation, mRNA:protamine complexes were shown to strongly induce innate immune response [73]. Scheel et al indicate that protamine condensed mRNA stimulates the immune system through a MyD88-dependent pathway, suggesting that TLR7 and TLR8 are probably the receptors involved [74].…”

“…This immune activating capacity of protamine can be exploited for vaccination strategies, but seemed to inhibit the primary goal of mRNA delivery, i.e. expression of the encoded protein [73]. Other well-investigated mRNA carriers are cationic lipids and polymers.…”