Evaluation of the immunogenicity of a Crimean-Congo hemorrhagic fever virus vaccine candidate in mice developed based on a baculovirus Zera nanoparticle delivery system

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease caused by Crimean-Congo hemorrhagic fever virus (CCHFV), which can cause severe clinical disease and even death in humans. In recent years, the disease has spread to a wider area, posing a major public health threat to China as well as the Middle East, Europe and Africa, and there is no safe and effective vaccine to prevent the disease. Recently, it has been shown that using the Zera fusion to target proteins can enhance immunogenicity and improve the potential for developing viral vaccines. Based on this finding, in this study, two vaccine candidates, Zera-Gn and Zera-Np, were prepared using an insect baculovirus system expressing CCHFV glycoprotein (Gn) and nucleocapsid protein (Np) fused with Zera tags, and evaluated for immunogenicity in BALB/c mice. The obtainedresults showed that both Zera-Gn and Zera-Np recombinant nanoparticles were successfully expressed, and Zera-Gn had good induction of humoral and cellular immunity in mice, and its immunogenicity was significantly higher than that of Zera-Np. The results indicated that Zera-Gn self-assembled nanoparticles prepared by fusing Zera tags with CCHFV spike-in protein Gn have the potential to be a candidate vaccine for CCHF, and this study provides a reference for the development of Zera self-assembled nanoparticle vaccine for CCHF.

Evaluation of the immunogenicity of vaccine candidates developed using a baculovirus surface display system for Crimean-Congo hemorrhagic fever virus in mice

Crimean-Congo hemorrhagic fever (CCHF), which has a fatality rate of 20–30%, is widely prevalent in several regions in Asia, Europe, and Africa and has spread to a wider range of areas in recent years. At present, there is a lack of safe and effective vaccines for the prevention of CCHF. In this study, we prepared three vaccine candidates, rvAc-Gn, rvAc-Np, and rvAc-Gn-Np, that encoded the CCHF virus (CCHFV) glycoprotein Gn and the nucleocapsid protein (Np) on the surface of baculovirus using an insect baculovirus vector expression system (BVES) and evaluated their immunogenicity in BALB/c mice. The experimental results showed that both CCHFV Gn and Np were expressed by the respective recombinant baculoviruses and anchored to the viral envelope. BALB/c mice were immunized, and all three recombinant baculoviruses showed significant humoral immunity. At the cellular level, the level of immunity in the rvAc-Gn group was significantly higher than that in the rvAc-Np and rvAc-Gn-Np groups, and the rvAc-Gn-Np coexpression group exhibited the lowest level of cellular immunity. In conclusion, the strategy of coexpressing Gn and Np in the baculovirus surface display system did not result in improvements in immunogenicity, whereas the recombinant baculovirus displaying Gn alone could induce significant humoral and cellular immunity in mice, indicating that rvAc-Gn has potential as a CCHF vaccine candidate. This study thus provides new ideas for the development of a CCHF baculovirus vaccine.

Partial IgA-Deficiency with Increased Th2-Type Cytokines in TGF-β1 Knockout Mice

Though it has been shown that TGF-β1 directs B cells to switch to IgA in vitro, no studies have assessed TGF-β1 effects on mucosal vs systemic immunity in vivo. When the B cell functions of TGF-β1 gene-disrupted (TGF-β1−/−) mice were analyzed, significantly decreased IgA levels and increased IgG and IgM levels in serum and external secretions were observed. Further, analysis of Ab forming cells (AFC) isolated from both mucosal and systemic lymphoid tissue showed elevated IgM, IgG, and IgE, with decreased IgA AFC. A lack of IgA-committed B cells was seen in TGF-β1−/− mice, especially in the gastrointestinal (GI) tract. Splenic T cells triggered via the TCR expressed elevated Th2-type cytokines and, consistent with this observation, a 31-fold increase in serum IgE was seen in TGF-β1−/− mice. Thus, uncontrolled B cell responses, which include elevated IgE levels, a lack of antiinflammatory IgA, and an excess of complement-binding IgG and IgM Abs, will promote inflammation at mucosal surfaces in TGF-β1−/− mice and likely contribute to pulmonary and GI tract lesions, ultimately leading to the early death of these mice.

Lymphotactin Acts as an Innate Mucosal Adjuvant

Lymphotactin (Lptn) is a C chemokine produced predominantly by NK and CD8-positive (CD8+) T cells including γδ TCR-positive (TCR+) intraepithelial lymphocytes. Lptn is chemotactic for NK and T cells and likely plays an important role in maintaining the integrity of the epithelium and in mucosal immune responses. In this study, we characterized the immune responses to OVA given intranasally with Lptn to mice. This regimen enhanced OVA-specific serum Ab responses and Ab titers in mucosal secretions. Lptn also enhanced OVA-specific Ab-forming cells in mucosal and systemic compartments. CD4-positive (CD4+) T cells isolated from mucosal compartments and spleens of mice intranasally immunized with OVA plus Lptn displayed higher OVA-specific proliferative responses and greater synthesis of IFN-γ, IL-2, IL-4, IL-5, IL-6, and IL-10 than did CD4+ T cells from mice given OVA without Lptn. These studies indicate that Lptn has adjuvant properties and suggest that Lptn present in the mucosa has the potential to enhance mucosal and systemic Ab responses through help provided by Th1- and Th2-type cells to link the initial innate signals of the mucosa with the acquired immune system.

IL-12 Is an Effective Adjuvant for Induction of Mucosal Immunity

We addressed the effects of two cytokines, IL-6 and IL-12, derived from APCs, for the development of mucosal IgA Ab responses following their nasal delivery with the protein vaccine tetanus toxoid (TT). Mice treated nasally with IL-6 and TT showed higher TT-specific serum IgG (mainly IgG1 and IgG2b) Ab responses than did control mice, but exhibited no IgE and negligible secretory IgA (S-IgA) Ab responses. In contrast, IL-12 administered nasally with TT not only induced sharp increases in TT-specific serum IgG (mainly IgG1 and IgG2b) and IgA, but also elevated mucosal S-IgA Ab responses. Coadministration of IL-6 and IL-12 with TT did not enhance the mucosal or serum Ab responses over those seen with IL-12 alone. TT-specific CD4+ T cells from mice given TT with IL-6 or IL-12 produced higher levels of IFN-γ, IL-6, and IL-10 than did those from control mice, but only negligible levels of IL-4 and IL-5. In summary, both intranasal IL-6 and IL-12 induced serum Abs that protected mice from systemic challenge with TT, whereas only IL-12 induced mucosal S-IgA Ab responses. The significance of IL-12-induced Th1-type responses for regulation of both mucosal and systemic immunity is discussed.

A Nontoxic Adjuvant for Mucosal Immunity to Pneumococcal Surface Protein A

In this study, we demonstrated that pneumococcal surface protein A (PspA) nasally administered with a nontoxic A subunit mutant of cholera toxin (mCT) S61F elicited a protective immune response. Immunization with PspA and mCT elicited higher levels of PspA-specific IgG and IgA Abs in serum and of IgG and IgA anti-PspA Ab-forming cells in spleens, cervical lymph nodes (CLN), and lung tissue when compared to nonimmunized mice. Furthermore, significant PspA-specific IgA Abs were induced in saliva and nasal secretions. These responses were dependent on the use of mCT as a mucosal adjuvant. The PspA-specific Ab responses induced by mCT S61F were comparable with those induced by native CT (nCT). Analysis of cytokine responses showed that nasal PspA plus mCT S61F enhanced the induction of PspA-specific CD4+ T cells producing IL-4 but not IFN-γ in CLN at both the protein and mRNA levels. Importantly, significant numbers of mice intranasally immunized with PspA plus mCT S61F were protected from lethal challenge with capsular serotype 3 Streptococcus pneumoniae A66. These results show that intranasal administration of PspA together with mCT S61F is an effective mucosal vaccine against pneumococcal infection and induces CD4+ Th2-type cells, which provide help for both mucosal and systemic Ab responses.

Repeated Intratracheal Instillations of Nonreplicating Adenovirus 2 Vector Attenuate CTL Responses and IFN-γ Production

The proposed usage of replication-deficient adenovirus (Ad) vectors for corrective gene therapy or for mucosal immunization has been limited in part by the host reactivity to the Ad vector, thus limiting repeated Ad instillations. We have recently shown that the reactivity to the Ad vector is in large part due to increased CD4+ Th1 and Th2 responses as well as elevated IgG and mucosal IgA responses. It has been recently proposed that the diminution of transgene expression in respiratory epithelia was due to increased CTL reactivity to expressed Ad proteins. Herein, we report that repeated intratracheal delivery of a second generation Ad2 vector into mice results in no detectable CTL activity in freshly isolated lymphoid cells from lungs, lower respiratory lymph nodes, or spleens or after in vitro restimulation. In contrast, a single dose of Ad2 vector did elicit a robust CTL response. This attenuation of CTL activity was long lived and was not affected by macrophage depletion or due to a reduction in CD4+ or CD8+ T cells. Examination of cytokine production via MHC class I or class II restimulation by lymphoid cells from three intratracheally treated mice showed an attenuation in the production of IFN-γ by as much as 110-fold. This reduction in IFN-γ could not be attributed to increased IL-4 or IL-10 production. Thus, this study shows that the CTL response to Ad vectors is attenuated upon repeated administration.