mRNA Vaccination for Treating Allergy by Modulating Allergen‐Specific Immunity

This News and Views article discusses the rationale for anti-allergy vaccine development using a lipid nanoparticle-mRNA platform. The authors provide additional evidence that supports the potential of using the mRNA approach to combat allergic diseases. Allergic diseases have become a significant global health issue with prevalence rates increasing over recent decades [1]. However, safe and long-lasting strategies to prevent or treat allergic disorders are still lacking, with the exception of active allergen avoidance, physical protective measures, or the intake of antihistamines upon accidental exposure. Recently, Rochman et al. reported the application of a lipid nanoparticle (LNP)-mRNA platform to develop anti-allergy vaccines [2], which coincided with our recent finding that ovalbumin (OVA)-mRNA-LNP and OVA-interleukin (IL)-10-mRNA-LNP vaccines demonstrate prophylactic efficacy against the onset of allergic responses [3]. Both studies proposed that an allergen-specific mRNA vaccine could shift Th2-type allergic immunity to a Th1 phenotype, and concomitantly elicit robust levels of allergen-specific immunoglobulin G (IgG) that block the immunoglobulin E (IgE)–allergen interaction. However, the rationale for using unmodified whole allergens in vaccine development remains uncertain based on the potential risk of allergenicity. Additionally, it remains to be determined whether Th1-type T cell responses or allergen-blocking antibodies play a more pivotal role in mediating anti-allergic effects. In this study, we further modified the allergen modality and accordingly constructed four mRNA sequences encoding: (1) Full-length OVA as we have reported previously [2]; (2) Full-length OVA attached to the lysosomal integral membrane protein-II (LIMP-II) that facilitates major histocompatibility complex (MHC)-II presentation; (3) Four tandem T cell epitopes (amino acids [aa] 37–51) of OVA connected to an invariant (Ii) chain (aa 1–80); and (4) Tandem repeats of two T cell epitopes (aa 37–51 and 147–161) of OVA downstream of the Ii chain sequence (Figure 1a). The mRNA sequences were further codon-optimized, synthesized, and encapsulated into LNPs using our well-established platforms [4-7] (Supporting Information S1). The four vaccine candidates were tested by immunizing BALB/c mice at a dose of 5 μg at a 7-day interval, followed by intraperitoneal sensitization and repeated intragastric challenge. Anaphylaxis was induced via a final intraperitoneal challenge with OVA (Figure 1b). On day 32 prior to sensitization, mice immunized with OVA-mRNA vaccine and OVA-LIMP-II-mRNA vaccine produced robust levels of anti-OVA IgG (Figure 1c). In contrast, the two T cell epitope-based mRNA vaccines did not elicit specific antibodies, which was likely due to the lack of OVA-specific B cell epitopes. Design and evaluation of allergen-specific mRNA vaccines. (a) Design of allergen-specific mRNA vaccine. (b) Experimental design. (c) OVA-specific IgG titer in mice following the administration of three doses of vaccine (n = 5–6/group). (d) Rectal temperature of mice was monitored upon allergen challenge (n = 5–6/group). Two-way ANOVA was employed for statistical analysis. (e) BALB/c mice were immunized with 5 μg of vaccine three times at an interval of 7 days. Two weeks after the final boost immunization, splenocytes were stimulated with OVA overlapping peptides (10 μg/mL) for 24 h. Cells without peptide stimulation were treated as negative controls. The frequencies of IFN-γ-, IL-2-, and IL-10-producing T cells were measured by ELISpot. OVA-specific cytokine-producing T cells were enumerated and are shown as spots per million stimulated splenocytes. Negative control values were subtracted. Data from representative animals are shown. One-way ANOVA with post hoc Tukey's test for correction was used for statistical analysis. *p < 0.05, **p < 0.01, ****p < 0.0001, ns denotes non-significant. IgG, immunoglobulin G; Ii, invariant; IL, interleukin; LIMP-II, lysosomal integral membrane protein-II; OVA, ovalbumin. Animals further underwent sensitization and challenge to achieve an allergic status to OVA. Upon final allergen challenge, rectal temperature, as one of the key parameters of anaphylaxis, was evaluated. Unvaccinated mice showed a rapid and pronounced decline in rectal temperature, whereas in contrast, animals that were immunized with OVA-mRNA, OVA-LIMP-II-mRNA, and Ii chain-epitope-mRNA (Design 1) vaccines were all protected from the onset of an allergic response to varying degrees (Figure 1d). Noticeably, the Ii chain-epitope-mRNA (Design 1) vaccine that failed to induce anti-OVA IgG also demonstrated superior protective efficacy compared with the two vaccines encoding full-length OVA. Modification of full-length OVA with LIMP-II peptides did not increase the protective capacity of OVA-mRNA vaccine. Another T cell epitope-mRNA (Design 2) vaccine constructed with Ii chain in conjugation with two different T cell epitopes of OVA demonstrated only marginal protective efficacy, which suggested that epitope immunodominance can affect vaccine efficacy and should be well evaluated during vaccine design. Importantly, these data indicated that allergen-specific Th1-type T cell immunity contributed greatly to protection. Next, we particularly focused on the three vaccine candidates showing protective efficacy and assessed their abilities at inducing Th1-type and regulatory T cell responses. The T cell epitope-based mRNA vaccine elicited remarkably higher levels of interferon-γ- and IL-2-producing T cells than OVA-mRNA and OVA-LIMP-II mRNA vaccines (Figure 1e). In addition, we found that the three vaccine candidates elicited comparable levels of OVA-specific IL-10+ T cells (Figure 1e), which resemble the phenotype of regulatory T cells and may therefore play a role in mitigating an allergic response. Previously, we reported that LNP-mRNA vaccines encoding unmodified full-length OVA allergen demonstrated a moderate prophylactic effect against the onset of allergic responses, which was likely mediated by both vaccine-induced allergen-blocking IgG and Th1-type T cell immunity counteracting an allergen-specific Th2-type response [3]. As a follow-up study, we showed that a T cell epitope-based mRNA vaccine demonstrated superior anti-allergy efficacy over an equivalent vaccine encoding a full-length allergen. This outcome appears to predominantly rely on the generation of strong Th1-biased T cells since allergen-blocking IgG was not elicited because of the lack of a specific B cell epitope. However, it should also be noted that the pre-vaccinated mice were not completely protected from anaphylaxis symptoms upon the final allergen challenge. The blocking effect of vaccine-induced non-IgE antibodies may still play an indispensable role in combating allergy; however, this awaits further in-depth investigations. These findings build upon our previous study and further highlight the potential of the mRNA platform in combating allergies. Among various vaccine platforms, mRNA vaccines have shown strong potential to promote Th1-type T cell and antibody responses as well as to generate regulatory T cells that help establish immune tolerance. These characteristics make the mRNA platform a promising option for developing anti-allergy therapy. However, some questions remain unresolved in this study. One noticeable aspect is the remarkably distinct efficacy of the two epitope-based mRNA vaccines. The vaccine constructed with four tandem repeated T cell epitopes exhibited robust protection, while the vaccine containing two different epitopes showed limited anti-allergy efficacy. This implies that the selection of an optimal T cell epitope or the method of construction may affect vaccine efficacy. In addition, T cell epitope competition may exist, which may lead to suppressed immune responses that compromise vaccine efficacy. Another point for consideration is the OVA-allergic animal model used in our study, which can only represent an intestinal allergic response not allergic reactions occurring in the upper respiratory tract. Whether the data reported in this context also hold true in other allergic animal models should be evaluated more comprehensively. Furthermore, an in-depth understanding of the mode-of-action of allergen-specific mRNA vaccines will be critical to guide rational vaccine design, including the modification of allergens, mRNA design, and optimization of the LNP carrier. Kun Guo: investigation (lead), methodology (equal), data curation (lead). Lijing Liu: investigation (equal), methodology (equal), data curation (equal). Mingyun Shen: methodology (supporting), supervision (supporting). Karin Loré: writing – review and editing (equal), supervision (supporting). Ang Lin: conceptualization (lead), methodology (lead), supervision (lead), funding acquisition (lead), writing – original draft (lead), validation (lead). The authors have nothing to report. This work was supported by National Natural Science Foundation of China (Grant 32471004) and the Innovation and Entrepreneurship (ShuangChuang) Program of Jiangsu Province (Grant JSSCTD202447). This work was performed in accordance with the Guidelines for the Care and Use of Laboratory Animals and was approved by the Institutional Animal Care and Use Committee of China Pharmaceutical University and the Ethical Committee of China Pharmaceutical University (Approval Number: VR-B2301P090). The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.