Robust specific RBD responses and neutralizing antibodies after ChAdOx1 nCoV-19 and CoronaVac vaccination in SARS-CoV-2- seropositive individuals.

Background: The pandemic unleashed by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected more than 500 million people worldwide and caused more than 6 million deaths. Cellular and humoral immunity induced by infection or immunization are key factors in controlling the viral burden and avoiding the recurrence of coronavirus disease. The duration and effectiveness of immunity after infection is relevant to pandemic policy interventions, including the timing of vaccine boosters. Objectives: We sought to evaluate longitudinal binding and functional antibodies against SARS-CoV-2 receptor-binding domain in police officers and health care workers with a history of coronavirus disease 2019 and compare with SARS-CoV-2-naive individuals after vaccination with adenovirus-based ChAdOx1 nCoV-19 (AstraZeneca-Fiocruz) or the inactivated CoronaVac vaccine (Sinovac-Butantan Institute). Methods: A total of 208 participants were vaccinated. Of these, 126 (60.57%) received the ChAdOx1 nCoV-19 vaccine and 82 (39.42%) received the CoronaVac vaccine. Prevaccination and postvaccination blood was collected, and the amount of anti-SARS-CoV-2 IgG and the neutralizing ability of the antibodies to block the interaction between angiotensin-converting enzyme 2 and receptor-binding domain were determined. Results: Subjects with preexisting SARS-CoV-2 immunity and who received a single dose of ChAdOx1 nCoV-19 or CoronaVac have similar or superior antibody levels when compared with levels in seronegative individuals even after 2 doses of the vaccine. Neutralizing antibody titers of seropositive individuals were higher with a single dose of either ChAdOx1 nCoV-19 or CoronaVac compared with those of seronegative individuals. After 2 doses, both groups reached a plateau response. Conclusions: Our data reinforce the importance of vaccine boosters to increase specific binding and neutralizing SARS-CoV-2 antibodies.

Diagnostic and vaccine potential of Zika virus envelope protein (E) derivates produced in bacterial and insect cells.

Introduction: In the present study we evaluated the features of different recombinant forms of Zika virus (ZIKV) proteins produced in either bacterial (Eschericha coli) or insect cells (Drosophila melanogaster). The ZIKV-envelope glycoprotein (EZIKV) is responsible for virus entry into host cells, is the main target of neutralizing antibodies and has been used as a target antigen either for serological tests or for the development of subunit vaccines. The EZIKV is composed of three structural and functional domains (EDI, EDII, and EDIII), which share extensive sequence conservation with the corresponding counterparts expressed by other flaviviruses, particularly the different dengue virus (DENV) subtypes. Methods: In this study, we carried out a systematic comparison of the antigenicity and immunogenicity of recombinant EZIKV, EDI/IIZIKV and EDIIIZIKV produced in E. coli BL21 and Drosophila S2 cells. For the antigenicity analysis we collected 88 serum samples from ZIKV-infected participants and 57 serum samples from DENV-infected. For immunogenicity, C57BL/6 mice were immunized with two doses of EZIKV, EDI/IIZIKV and EDIIIZIKV produced in E. coli BL21 and Drosophila S2 cells to evaluate humoral and cellular immune response. In addition, AG129 mice were immunized with EZIKV and then challenge with ZIKV. Results: Testing of samples collected from ZIKV-infected and DENV-infected participants demonstrated that the EZIKV and EDIIIZIKV produced in BL21 cells presented better sensitivity and specificity compared to proteins produced in S2 cells. In vivo analyses were carried out with C57BL/6 mice and the results indicated that, despite similar immunogenicity, antigens produced in S2 cells, particularly EZIKV and EDIIIZIKV, induced higher ZIKV-neutralizing antibody levels in vaccinated mice. In addition, immunization with EZIKV expressed in S2 cells delayed the onset of symptoms and increased survival rates in immunocompromised mice. All recombinant antigens, either produced in bacteria or insect cells, induced antigen-specific CD4+ and CD8+ T cell responses. Conclusion: In conclusion, the present study highlights the differences in antigenicity and immunogenicity of recombinant ZIKV antigens produced in two heterologous protein expression systems.

Multiple-Allele MHC Class II Epitope Engineering by a Molecular Dynamics-Based Evolution Protocol.

Epitopes that bind simultaneously to all human alleles of Major Histocompatibility Complex class II (MHC II) are considered one of the key factors for the development of improved vaccines and cancer immunotherapies. To engineer MHC II multiple-allele binders, we developed a protocol called PanMHC-PARCE, based on the unsupervised optimization of the epitope sequence by single-point mutations, parallel explicit-solvent molecular dynamics simulations and scoring of the MHC II-epitope complexes. The key idea is accepting mutations that not only improve the affinity but also reduce the affinity gap between the alleles. We applied this methodology to enhance a Plasmodium vivax epitope for multiple-allele binding. In vitro rate-binding assays showed that four engineered peptides were able to bind with improved affinity toward multiple human MHC II alleles. Moreover, we demonstrated that mice immunized with the peptides exhibited interferon-gamma cellular immune response. Overall, the method enables the engineering of peptides with improved binding properties that can be used for the generation of new immunotherapies.

ZIKV-envelope proteins induce specific humoral and cellular immunity in distinct mice strains.

Recent outbreaks of Zika virus (ZIKV) infection have highlighted the need for a better understanding of ZIKV-specific immune responses. The ZIKV envelope glycoprotein (EZIKV) is the most abundant protein on the virus surface and it is the main target of the protective immune response. EZIKV protein contains the central domain (EDI), a dimerization domain containing the fusion peptide (EDII), and a domain that binds to the cell surface receptor (EDIII). In this study, we performed a systematic comparison of the specific immune response induced by different EZIKV recombinant proteins (EZIKV, EDI/IIZIKV or EDIIIZIKV) in two mice strains. Immunization induced high titers of E-specific antibodies which recognized ZIKV-infected cells and neutralized the virus. Furthermore, immunization with EZIKV, EDI/IIZIKV and EDIIIZIKV proteins induced specific IFNγ-producing cells and polyfunctional CD4+ and CD8+ T cells. Finally, we identified 4 peptides present in the envelope protein (E1-20, E51-70, E351-370 and E361-380), capable of inducing a cellular immune response to the H-2Kd and H-2Kb haplotypes. In summary, our work provides a detailed assessment of the immune responses induced after immunization with different regions of the ZIKV envelope protein.

Zika virus-an update on the current efforts for vaccine development.

In 2015, the world witnessed the resurgence and global spread of Zika virus (ZIKV). This arbovirus infection is associated with Guillain-Barré syndrome in adults and with devastating congenital malformations during pregnancy. Despite scientific efforts, the development of a vaccine capable of inducing long-term protection has been challenging. Without a safe and efficacious licensed vaccine, control of virus transmission is based on vector control, but this strategy has been shown to be inefficient. An effective and protective vaccine relies on several requirements, which include: (i) induction of specific immune response against immunodominant antigens; (ii) selection of adjuvant-antigen formulation; and (iii) assessment of safety, effectiveness, and long-term protection. In this commentary, we provide a brief overview about the current efforts for the development of an efficacious ZIKV vaccine, covering the most important preclinical trials up to the formulations that are now being evaluated in clinical trials.

Homologous prime-boost with Zika virus envelope protein and poly (I:C) induces robust specific humoral and cellular immune responses.

The recent outbreaks of Zika virus (ZIKV) infection and the potential association with Guillain-Barré syndrome in adults and with congenital abnormalities have highlighted the urgency for an effective vaccine. The ZIKV Envelope glycoprotein (EZIKV) is the most abundant protein on the virus surface, and has been evaluated together with the pre-membrane protein (prM) of the viral coat as a vaccine candidate in clinical trials. In this study, we performed a head-to-head comparison of the immune response induced by different EZIKV-based vaccine candidates in mice. We compared different platforms (DNA, recombinant protein), adjuvants (poly (I:C), CpG ODN 1826) and immunization strategies (homologous, heterologous). The hierarchy of adjuvant potency showed that poly (I:C) was a superior adjuvant than CpG ODN. While poly (I:C) assisted immunization reached a plateau in antibody titers after two doses, the CpG ODN group required an extra immunization dose. Besides, the administration of poly (I:C) induced higher EZIKV-specific cellular immune responses than CpG ODN. We also show that immunization with homologous prime-boost EZIKV protein + poly (I:C) regimen induced a more robust humoral response than homologous DNA (pVAX-EZIKV) or heterologous regimens (DNA/protein or protein/DNA). A detailed analysis of cellular immune responses revealed that homologous (EZIKV + poly (I:C)) and heterologous (pVAX-EZIKV/EZIKV + poly (I:C)) prime-boost regimens induced the highest magnitude of IFN-γ secreting cells and cytokine-producing CD4+ T cells. Overall, our data demonstrate that homologous EZIKV + poly (I:C) prime-boost immunization is sufficient to induce more robust specific-EZIKV humoral and cellular immune responses than the other strategies that contemplate homologous DNA (pVAX-EZIKV) or heterologous (pVAX-EZIKV/EZIKV + poly (I:C), and vice-versa) immunizations.

Poly(I:C) Potentiates T Cell Immunity to a Dendritic Cell Targeted HIV-Multiepitope Vaccine.

Cellular immune responses are implicated in resistance to HIV and have been considered for the development of an effective vaccine. Despite their safety profile, subunit vaccines need to be delivered combined with an adjuvant. In the last years, in vivo antigen targeting to dendritic cells (DCs) using chimeric monoclonal antibodies (mAb) against the DC endocytic receptor DEC205/CD205 was shown to support long-term T cell immunity. Here, we evaluated the ability of different adjuvants to modulate specific cellular immune response when eight CD4+ HIV-derived epitopes (HIVBr8) were targeted to DEC205+ DCs in vivo. Immunization with two doses of αDECHIVBr8 mAb along with poly(I:C) induced Th1 cytokine production and higher frequency of HIV-specific polyfunctional and long-lived T cells than MPL or CpG ODN-assisted immunization. Although each adjuvant elicited responses against the 8 epitopes present in the vaccine, the magnitude of the T cell response was higher in the presence of poly(I:C). Moreover, poly(I:C) up regulated the expression of costimulatory molecules in both cDC1 and cDC2 DCs subsets. In summary, the use of poly(I:C) in a vaccine formulation that targets multiple epitopes to the DEC205 receptor improved the potency and the quality of HIV-specific responses when compared to other vaccine-adjuvant formulations. This study highlights the importance of the rational selection of antigen/adjuvant combination to potentiate the desired immune responses.

Dendritic Cell Targeting Effectively Boosts T Cell Responses Elicited by an HIV Multiepitope DNA Vaccine.

Despite several efforts in the last decades, an efficacious HIV-1 vaccine is still not available. Different approaches have been evaluated, such as recombinant proteins, viral vectors, DNA vaccines, and, most recently, dendritic cell (DC) targeting. This strategy is based on DC features that place them as central for induction of immunity. Targeting is accomplished by the use of chimeric monoclonal antibodies directed to DC surface receptors fused to the antigen of interest. In this work, we targeted eight promiscuous HIV-derived CD4+ T cell epitopes (HIVBr8) to the DEC205+ DCs by fusing the multiepitope immunogen to the heavy chain of αDEC205 (αDECHIVBr8), in the presence of the TLR3 agonist poly (I:C). In addition, we tested a DNA vaccine encoding the same epitopes using homologous or heterologous prime-boost regimens. Our results showed that mice immunized with αDECHIVBr8 presented higher CD4+ and CD8+ T cell responses when compared to mice that received the DNA vaccine (pVAXHIVBr8). In addition, pVAXHIVBr8 priming followed by αDECHIVBr8 boosting induced higher polyfunctional proliferative and cytokine-producing T cell responses to HIV-1 peptides than homologous DNA immunization or heterologous αDEC prime/DNA boost. Based on these results, we conclude that homologous prime-boost and heterologous boosting immunization strategies targeting CD4+ epitopes to DCs are effective to improve HIV-specific cellular immune responses when compared to standalone DNA immunization. Moreover, our results indicate that antigen targeting to DC is an efficient strategy to boost immunity against a multiepitope immunogen, especially in the context of DNA vaccination.

Adjuvants: Classification, Modus Operandi, and Licensing.

Vaccination is one of the most efficient strategies for the prevention of infectious diseases. Although safer, subunit vaccines are poorly immunogenic and for this reason the use of adjuvants is strongly recommended. Since their discovery in the beginning of the 20th century, adjuvants have been used to improve immune responses that ultimately lead to protection against disease. The choice of the adjuvant is of utmost importance as it can stimulate protective immunity. Their mechanisms of action have now been revealed. Our increasing understanding of the immune system, and of correlates of protection, is helping in the development of new vaccine formulations for global infections. Nevertheless, few adjuvants are licensed for human vaccines and several formulations are now being evaluated in clinical trials. In this review, we briefly describe the most well known adjuvants used in experimental and clinical settings based on their main mechanisms of action and also highlight the requirements for licensing new vaccine formulations.