Cricket paralysis virus internal ribosome entry site-derived RNA promotes conventional vaccine efficacy by enhancing a balanced Th1/Th2 response

Abstract

Keywords:MERS HPV CrPV IRES RNA Adjuvant Vaccine Th1/Th2 Alum a b s t r a c t An ideal adjuvant should increase vaccine efficacy through balanced Th1/Th2 responses and be safe to use. Recombinant protein-based vaccines are usually formulated with aluminum (alum)-based adjuvants to ensure an adequate immune response. However, use of alum triggers a Th2-biased immune induction, and hence is not optimal. Although the adjuvanticity of RNA has been reported, a systematic and overall investigation on its efficacy is lacking. We found that single strand RNA (termed RNA adjuvant) derived from cricket paralysis virus intergenic region internal ribosome entry site induced the expression of various adjuvant-function-related genes, such as type 1 and 2 interferon (IFN) and toll-like receptor (TLR), T cell activation, and leukocyte chemotaxis in human peripheral blood mononuclear cells; furthermore, its innate and IFN transcriptome profile patterns were similar to those of a live-attenuated yellow fever vaccine. This suggests that protein-based vaccines formulated using RNA adjuvant function as liveattenuated vaccines. Application of the RNA adjuvant in mouse enhanced the efficacy of Middle East respiratory syndrome spike protein, a protein-subunit vaccine and human papillomavirus L1 protein, a virus-like particle vaccine, by activating innate immune response through TLR7 and enhancing pAPC chemotaxis, leading to a balanced Th1/Th2 responses. Moreover, the combination of alum and the RNA adjuvant synergistically induced humoral and cellular immune responses and endowed long-term immunity. Therefore, RNA adjuvants have broad applicability and can be used with all conventional vaccines to improve vaccine efficacy qualitatively and quantitively.

MERS-CoV Spike Protein Vaccine and Inactivated Influenza Vaccine Formulated with Single Strand RNA Adjuvant Induce T-Cell Activation through Intranasal Immunization in Mice

“…Moreover, RNA adjuvant groups (G3 and G6) more effectively induced antibody titers than others (Figure 2A,B). These results agree with those of a previous report [17]. Interestingly, only G9, which was immunized with MERS S protein, alum, and RNA adjuvant, induced IgA in the BALF (Figure 2C), which was strongly correlated with the mucosal immune system [32].…”

“…However, G2 (intramuscularly immunized with only MERS S protein) showed higher NAb levels than G5 (intradermally immunized with only MERS S protein) ( Figure 2B). G2 and G5, which were immunized only with MERS S protein, produced lower NAb levels than those of G3 and G6, which were immunized with MERS S protein, alum, and RNA adjuvant, in agreement with a previous report [17]. As expected, no intranasally immunized groups produced NAbs ( Figure 2B).…”

“…Additionally, side effects such as autoimmune/inflammatory syndrome induced by adjuvants also occur, requiring further confirmation of safety [30,31]. To compensate for these limitations, RNA adjuvants have recently been developed [19] and applied to MERS and influenza, as they did not accumulate in the body, thus lowering the risk of side effects and effectively increasing the immune response [17,18]. We found that immunization with MERS S protein with RNA adjuvant and alum synergistically induced the humoral immune response and led to balanced Th1/Th2 responses [17].…”

“…To compensate for these limitations, RNA adjuvants have recently been developed [19] and applied to MERS and influenza, as they did not accumulate in the body, thus lowering the risk of side effects and effectively increasing the immune response [17,18]. We found that immunization with MERS S protein with RNA adjuvant and alum synergistically induced the humoral immune response and led to balanced Th1/Th2 responses [17]. However, the immunization routes most suitable for inducing the optimal immune response with RNA adjuvant were unclear.…”

“…RNA adjuvant is a single-stranded RNA. Thus, it can activate the innate immune response through TLR7 or TLR8 [17]. Therefore, such TLR activation may contribute to IgA class switching.…”