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The unprecedented global impact caused by SARS-CoV-2 imposed huge health and economic challenges, highlighting the urgent need for safe and effective vaccines. The receptor-binding domain (RBD) of SARS-CoV-2 is the major target for neutralizing antibodies and for vaccine formulations. Nonetheless, the low immunogenicity of the RBD requires the use of alternative strategies to enhance its immunological properties. Here, we evaluated the use of a subunit vaccine antigen generated after the genetic fusing of the RBD with a mouse IgG antibody. Subcutaneous administration of RBD-IgG led to the extended presence of the protein in the blood of immunized animals and enhanced RBD-specific IgG titers. Furthermore, RBD-IgG immunized mice elicited increased virus neutralizing antibody titers, measured both with pseudoviruses and with live original (Wuhan) SARS-CoV-2. Immunized K18-hACE2 mice were fully resistant to the lethal challenge of the Wuhan SARS-CoV-2, demonstrated by the control of body-weight loss and virus loads in their lungs and brains. Thus, we conclude that the genetic fusion of the RBD with an IgG molecule enhanced the immunogenicity of the antigen and the generation of virus-neutralizing antibodies, supporting the use of IgG chimeric antigens as an approach to improve the performance of SARS-CoV-2 subunit vaccines.

Dengue is an infectious disease of global health concern that continues to require surveillance. Serological testing has been used to investigate dengue-infected patients, but specificity is affected by the co-circulation of ZIKA virus (ZIKV), which shares extensive antigen similarities. The goal of this study was the development of a specific dengue virus (DENV) IgG ELISA based on a multi-epitope NS1-based antigen for antibody detection. The multi-epitope protein (T-ΔNS1), derived from a fragment of the NS1-protein of the four DENV serotypes, was expressed in Escherichia coli and purified via affinity chromatography. The antigenicity and specificity were evaluated with sera of mice infected with DENV-1-4 or ZIKV or after immunization with the recombinant ΔNS1 proteins. The performance of the T-ΔNS1-based IgG ELISA was also determined with human serum samples. The results demonstrate that the DENV T-ΔNS1 was specifically recognized by the serum IgG of dengue-infected mice or humans but showed no or reduced reactivity with ZIKV-infected subjects. Based on the available set of clinical samples, the ELISA based on the DENV T-ΔNS1 achieved 77.42% sensitivity and 88.57% specificity. The results indicate that the T-ΔNS1 antigen is a promising candidate for the development of specific serological analysis.

The C-terminal portion of the E protein, known as stem, is conserved among flaviviruses and is an important target to peptide-based antiviral strategies. Since the dengue (DENV) and Zika (ZIKV) viruses share sequences in the stem region, in this study we evaluated the cross-inhibition of ZIKV by the stem-based DV2 peptide (419-447), which was previously described to inhibit all DENV serotypes. Thus, the anti-ZIKV effects induced by treatments with the DV2 peptide were tested in both in vitro and in vivo conditions. Molecular modeling approaches have demonstrated that the DV2 peptide interacts with amino acid residues exposed on the surface of pre- and postfusion forms of the ZIKA envelope (E) protein. The peptide did not have any significant cytotoxic effects on eukaryotic cells but efficiently inhibited ZIKV infectivity in cultivated Vero cells. In addition, the DV2 peptide reduced morbidity and mortality in mice subjected to lethal challenges with a ZIKV strain isolated in Brazil. Taken together, the present results support the therapeutic potential of the DV2 peptide against ZIKV infections and open perspectives for the development and clinical testing of anti-flavivirus treatments based on synthetic stem-based peptides.

As mRNA vaccines have proved to be very successful in battling the coronavirus disease 2019 (COVID-19) pandemic, this new modality has attracted widespread interest for the development of potent vaccines against other infectious diseases and cancer. Cervical cancer caused by persistent human papillomavirus (HPV) infection is a major cause of cancer-related deaths in women, and the development of safe and effective therapeutic strategies is urgently needed. In the present study, we compared the performance of three different mRNA vaccine modalities to target tumors associated with HPV-16 infection in mice. We generated lipid nanoparticle (LNP)-encapsulated self-amplifying mRNA as well as unmodified and nucleoside-modified non-replicating mRNA vaccines encoding a chimeric protein derived from the fusion of the HPV-16 E7 oncoprotein and the herpes simplex virus type 1 glycoprotein D (gDE7). We demonstrated that single low-dose immunizations with any of the three gDE7 mRNA vaccines induced activation of E7-specific CD8 + T cells, generated memory T cell responses capable of preventing tumor relapses, and eradicated subcutaneous tumors at different growth stages. In addition, the gDE7 mRNA-LNP vaccines induced potent tumor protection in two different orthotopic mouse tumor models after administration of a single vaccine dose. Last, comparative studies demonstrated that all three gDE7 mRNA-LNP vaccines proved to be superior to gDE7 DNA and gDE7 recombinant protein vaccines. Collectively, we demonstrated the immunogenicity and therapeutic efficacy of three different mRNA vaccines in extensive comparative experiments. Our data support further evaluation of these mRNA vaccines in clinical trials.

The development of safe and effective vaccine formulations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents a hallmark in the history of vaccines. Here we report a COVID-19 subunit vaccine based on a SARS-CoV-2 Spike protein receptor binding domain (RBD) incorporated into nano-multilamellar vesicles (NMV) associated with monophosphoryl lipid A (MPLA). The results based on immunization of C57BL/6 mice demonstrated that recombinant antigen incorporation into NMVs improved antibody and T-cell responses without inducing toxic effects under both in vitro and in vivo conditions. Administration of RBD-NMV-MPLA formulations modulated antigen avidity and IgG subclass responses, whereas MPLA incorporation improved the activation of CD4 + /CD8 + T-cell responses. In addition, immunization with the complete vaccine formulation reduced the number of doses required to achieve enhanced serum virus-neutralizing antibody titers. Overall, this study highlights NMV/MPLA technology, displaying the performance improvement of subunit vaccines against SARS-CoV-2, as well as other infectious diseases., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Chikungunya virus (CHIKV) is responsible for a self-limited illness that can evolve into long-lasting painful joint inflammation. In this study, we report a novel experimental CHIKV vaccine formulation of lipid nanoparticles loaded with a recombinant protein derived from the E2 structural protein. This antigen fragment, designated ∆E2.1, maintained the antigenicity of the native viral protein and was specifically recognized by antibodies induced in CHIKV-infected patients. The antigen has been formulated into nanoparticles consisting of nano-multilamellar vesicles (NMVs) combined with the adjuvant monophosphoryl lipid A (MPLA). The vaccine formulation demonstrated a depot effect, leading to controlled antigen release, and induced strong antibody responses significantly higher than in mice immunized with the purified protein combined with the adjuvant. More relevantly, E2-specific antibodies raised in mice immunized with ∆E2.1-loaded NMV-MPLA neutralized CHIKV under in vitro conditions. Taken together, the results demonstrated that the new nanoparticle-based vaccine formulation represents a promising approach for the development of effective anti-CHIKV vaccines., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Although active immunotherapies are effective strategies to induce activation of CD8 + T cells, advanced stage tumors require further improvements for efficient control. Concerning the burden of cancer-related to Human papillomavirus (HPV), particularly the high incidence and mortality of cervical cancer, our group developed an approach based on a DNA vaccine targeting the HPV-16 E7 oncoprotein (pgDE7h). This immunotherapy is capable of inducing an antitumour CD8 + T cell response but show only partial control of tumors in more advanced growth stages. Here, we combined a chemotherapeutic agent (gemcitabine- Gem) with pgDE7h to overcome immunosuppression and improve antitumour responses in a preclinical mouse tumor model. Our results demonstrated that administration of Gem had synergistic antitumor effects when combined with pgDE7h leading to eradication of both early-stages and established tumors. Overall, the antiproliferative effects of Gem observed in vitro and in vivo provided an optimal window for immunotherapy. In addition, the enhanced antitumour responses induced by the combined therapeutic regimen included enhanced frequencies of antigen-presenting cells (APCs), E7-specific IFN-γ-producing CD8 + T cells, and cytotoxic CD8 + T cells and, concomitantly, less pronounced accumulation of immunosuppressive myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). These findings demonstrated that the combination of Gem and an active immunotherapy strategy show increased effectiveness, leading to a reduced need for multiple drug doses and, therefore, decreased deleterious side effects avoiding resistance and tumor relapses. Altogether, our results provide evidence for a new and feasible chemoimmunotherapeutic strategy that supports future clinical translation., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2021 The Author(s). Published with license by Taylor & Francis Group, LLC.)

Self-assembling proteins may be generated after the addition of short specific amino acid sequences at both the N- and C-terminal ends. To date, this approach has not been evaluated regarding the impact of self-assembled proteins on the induction of immune responses. In the present study, we report the application of this experimental approach to the immunogenicity of protein antigens by measuring the antibody responses in mice immunized with nanoparticles made with a recombinant form of Zika virus nonstructural protein 1 (∆NS1). The results clearly indicated that ∆NS1-derived nanoparticles (NP-∆NS1) are assembled into a 3-dimensional structure with a high degree of multimerization. While ∆NS1 proved to be a weak immunogen, immunization with NP-∆NS1 enhanced subunit vaccines' immunogenicity with improved longevity in vaccinated mice. Thus, immunization with self-assembled antigens (nanovaccines) represents a new and promising strategy to enhance NS1-specific antibodies' induction based on purified recombinant proteins., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Zika virus (ZIKV) is a globally-distributed flavivirus transmitted to humans by Aedes mosquitoes, usually causing mild symptoms that may evolve to severe conditions, including neurological alterations, such as neonatal microcephaly and Guillain-Barré syndrome. Due to the absence of specific and effective preventive methods, we designed a new subunit vaccine based on a DNA vector (pgDNS1-ZIKV) encoding the non-structural protein 1 (NS1) genetically fused to the Herpes Simplex Virus (HSV) glycoprotein D (gD) protein. Recombinant plasmids were replicated in Escherichia coli and the expression of the target protein was confirmed in transfected HEK293 cells. C57BL/6 and AB6 (IFNAR1-/-) mice were i.m. immunized by electroporation in order to evaluate pgDNS1-ZIKV immunogenicity. After two doses, high NS1-specific IgG antibody titers were measured in serum samples collected from pgDNS1-ZIKV-immunized mice. The NS1-specific antibodies were capable to bind the native protein expressed in infected mammalian cells. Immunization with pgDNS1-ZIKV increased both humoral and cellular immune responses regarding mice immunized with a ZIKV NS1 encoding vaccine. Immunization with pgDNS1-ZIKV reduced viremia and morbidity scores leading to enhanced survival of immunodeficient AB6 mice challenged with a lethal virus load. These results give support to the use of ZIKV NS1 as a target antigen and further demonstrate the relevant adjuvant effects of HSV-1 gD., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Pereira, Alves, Sales, Andreata-Santos, Venceslau-Carvalho, Pereira, Castro-Amarante, Rodrigues-Jesus, Favaro, Chura-Chambi, Morganti and Ferreira.)

In the present study, we evaluated the immunological responses induced by dengue vaccines under experimental conditions after delivery via a transcutaneous (TC) route. Vaccines against type 2 Dengue virus particles (DENV2 New Guinea C (NGC) strain) combined with enterotoxigenic Escherichia coli (ETEC) heat-labile toxin (LT) were administered to BALB/c mice in a three-dose immunization regimen via the TC route. As a control for the parenteral administration route, other mouse groups were immunized with the same vaccine formulation via the intradermic (ID) route. Our results showed that mice vaccinated either via the TC or ID routes developed similar protective immunity, as measured after lethal challenges with the DENV2 NGC strain. Notably, the vaccine delivered through the TC route induced lower serum antibody (IgG) responses with regard to ID-immunized mice, particularly after the third dose. The protective immunity elicited in TC-immunized mice was attributed to different antigen-specific antibody properties, such as epitope specificity and IgG subclass responses, and cellular immune responses, as determined by cytokine secretion profiles. Altogether, the results of the present study demonstrate the immunogenicity and protective properties of a dengue vaccine delivered through the TC route and offer perspectives for future clinical applications.