The poxvirus Modified Vaccinia virus Ankara (MVA) is a safe and versatile licensed vaccine and viral vector, yet its immunogenicity remains improvable, as it often requires multiple doses for optimal protection and also induces waning of antibody responses. To enable more rational optimization of MVA-based vaccines, we developed a mechanistic and executable systems vaccinology framework based on Boolean modeling to capture the dynamics of vaccine-induced immune responses. We constructed and calibrated a Boolean network of the MVA‑induced immune response by integrating literature‑derived mechanisms with longitudinal in vivo experimental data. The model accurately reproduced immune dynamics with high fidelity and, importantly, was validated against independent datasets of genetically modified MVA vaccines, demonstrating strong predictive capacity. Using this framework, we performed in silico perturbations to evaluate novel genetically modified MVA mutants derived from expert knowledge. To further guide rational design, we built two other vaccine-induced response Boolean networks: one describing the MVA response in a broader fashion, the other modeling the YF‑17D yellow fever vaccine response that represents a reference for durable protection after single‑dose immunization. Comparative analysis of network topology and dynamics revealed shared and divergent features that informed strategies to enhance MVA-induced responses by reorienting them toward YF-17D-like immune signatures, and allowed us to design and test virtually two new genetically modified MVA deletion mutants. Throughout this work, we exploited the executable nature of the models of response to MVA to simulate perturbations, identifying potential targets to boost immunogenicity. Together, this work establishes executable Boolean modeling as a valuable predictive tool for systems vaccinology and provides a generalizable framework for the rational design and optimization of next‑generation MVA‑based vaccines.

Although mRNA-based COVID-19 vaccines have demonstrated high efficacy, their widespread global use remains constrained by high production costs and cold-chain requirements. Modified vaccinia virus Ankara (MVA) is a highly attenuated and thermostable viral vector with low production costs, potent immunogenicity, and strong potential for global distribution. Here, we compared head-to-head the long-term immunogenicity and efficacy of an MVA-based vaccine candidate with an approved mRNA vaccine in K18-hACE2 mice, both expressing the SARS-CoV-2 Omicron XBB.1.5 spike (S) protein. Mice received by intramuscular route homologous (mRNA/mRNA and MVA/MVA), heterologous (mRNA/MVA), or single-dose MVA regimens. SARS-CoV-2-specific humoral and cellular responses were evaluated at 10 days and 9 months after the last vaccination, as well as antibody levels at intermediate time points, and protection was assessed following intranasal SARS-CoV-2 XBB.1.5 challenge at 9 months post-vaccination. Binding IgG antibodies against the XBB.1.5 S protein remained high throughout the 9-month period in all vaccinated groups, whereas neutralizing antibody titers peaked early after the last vaccination and progressively declined, converging across regimens over time. S-specific CD8+ T-cell responses were strongest in mRNA-containing regimens at day 10 after the last vaccination and, although they contracted over time, they remained detectable at 9 months after the last vaccination in all two-dose groups, with a trend toward enhanced persistence in the heterologous mRNA/MVA regimen. In contrast, S-specific CD4+ T-cell responses remained low across all groups. All two-dose regimens markedly reduced viral RNA levels and infectious viral titers in both the upper and lower respiratory tract following SARS-CoV-2 XBB.1.5 challenge. Transcriptomic analysis of lung tissue after virus challenge revealed reduced expression of genes associated with inflammatory myeloid responses, interferon signalling and cellular stress in vaccinated mice compared with infected controls. Distinct post-challenge lung transcriptional profiles were observed across vaccination regimens, with differential modulation of genes associated with humoral, innate, and cellular immune responses. Overall, our findings demonstrate that MVA-based vaccination induces durable immunity in mice and achieves long-term control of SARS-CoV-2 XBB.1.5 replication comparable to that of mRNA vaccination, supporting its use as an alternative and complementary vaccine platform against SARS-CoV-2 and other emerging respiratory viruses.

IntroductionThe emergence of immune-evasive SARS-CoV-2 variants has exposed limitations in the breadth and durability of protection conferred by current Spike-based vaccines, highlighting the need for next-generation approaches targeting conserved viral regions. Here, we describe the design and preclinical evaluation of an optimized multi-epitope vaccine, CoV2-BMEPu.MethodsCoV2-BMEPu was rationally designed using immunological data from SARS-CoV-2 convalescent cohorts, incorporating conserved and immunodominant regions from the Spike (S), Membrane (M) and Nucleocapsid (N) proteins, together with selected receptor-binding domain (RBD) segments associated with broadly neutralizing antibodies. The construct was engineered as a secreted trimeric antigen and delivered as an mRNA vaccine formulated in lipid nanoparticles (LNPs). In vitro expression, innate immune activation, immunogenicity and protective efficacy were evaluated in cell systems and mouse models.ResultsmRNA-BMEPu was efficiently expressed in vitro as soluble oligomers and triggered innate immune activation in human macrophages. In C57BL/6 mice, LNP-BMEPu elicited robust binding and neutralizing antibodies against the ancestral virus and antigenically distant Omicron subvariants. Vaccination also induced strong and polyfunctional CD8⁺ T cell and T follicular helper responses that persisted over time. In K18-hACE2 transgenic mice, immunization conferred complete protection against lethal SARS-CoV-2 challenge, with effective control of viral replication and reduced lung inflammation.DiscussionThese results support CoV2-BMEPu as a next-generation multi-epitope mRNA vaccine candidate capable of inducing broad, durable and protective immunity against current and emerging SARS-CoV-2 variants.

The emergence of SARS-CoV-2 variants has highlighted the need for vaccines that complement Spike-directed immunity by targeting conserved T-cell responses. Here, we developed CoV2-TMEPu, a human-informed multi-patch immunogen integrating conserved and naturally immunodominant regions from structural, accessory and replication-associated SARS-CoV-2 proteins into a single mRNA-lipid nanoparticle (LNP) vaccine. LNP-CoV2-TMEPu was efficiently expressed in vitro and induced early innate immune activation. Homologous prime-boost immunization elicited robust, durable and polyfunctional CD8⁺ T-cell responses together with lower-magnitude CD4⁺ responses. Epitope mapping revealed broad but hierarchically organized multispecific recognition spanning multiple viral proteins and a diversified CD8⁺ memory phenotype. Vaccination also induced cross-reactive neutralizing activity against antigenically distinct Omicron-derived variants and protected K18-hACE2 mice from a lethal SARS-CoV-2 challenge, reducing disease severity and viral burden. Together, these findings establish human-informed multi-patch immunogen design as a promising strategy for next-generation variant-resilient coronavirus vaccines.

Despite the success of current COVID-19 vaccines, the immunity they generate wanes over time, requiring periodic boosters. The limited durability of memory responses, particularly from mRNA vaccines, remains a major challenge for achieving long-term protection. Developing vaccines that induce more sustained immunity would lessen the need for frequent revaccination, improving global vaccination logistics, especially in resource-limited settings. DNA-launched self-amplifying RNA replicons (DREP) and modified vaccinia virus Ankara (MVA) vectors are promising vaccine platforms capable of inducing potent humoral and cellular immunity. In this study, we evaluated SARS-CoV-2-specific immune responses in C57BL/6 mice following homologous and heterologous prime/boost regimens combining DREP- and MVA-based vaccines expressing the spike (S) protein from either the ancestral Wuhan strain or the Omicron XBB.1.5 variant. Homologous (DREP/DREP, MVA/MVA) and heterologous (DREP/MVA) regimens were followed for six months. MVA-S(3P)-based boosters elicited robust and durable anti-S IgG antibodies cross-recognizing multiple variants, with minimal decay over time. Neutralization mapped to the booster antigen: MVA-S(3PWuhan) induced neutralization of the ancestral strain, while MVA-S(3PXBB.1.5) selectively neutralized Omicron subvariants, maintaining high titers for at least six months. MVA-S(3P) boosters also enhanced antibody Fc-effector functions, memory B cells, and T follicular helper responses. Early after boosting, heterologous DREP/MVA regimens induced stronger CD4⁺ and CD8⁺ T-cell responses, while at six months all MVA-S(3P)-boosted groups maintained superior, long-lived cellular immunity. Collectively, MVA-S(3P)-based boosters improved the magnitude, breadth, and durability of humoral and cellular responses, supporting their strategic use in homologous and heterologous DREP/MVA vaccination regimens against SARS-CoV-2 and emerging variants.

Monkeypox virus (MPXV) is a poxvirus endemic to Central and West Africa with high epidemic potential. Poxviruses enter host cells via a conserved entry-fusion complex (EFC), which mediates viral fusion to the cell membrane. The EFC is a promising therapeutic target, but the absence of structural data has limited the development of fusion-inhibiting treatments. Here, we investigated A16/G9, a subcomplex of the EFC that controls fusion timing. Using cryo-electron microscopy, we showed how A16/G9 interacts with A56/K2, a viral fusion suppressor that prevents superinfection. Immunization with A16/G9 elicited a protective immune response in mice. Using X-ray crystallography, we characterized two neutralizing antibodies and engineered a chimeric antibody that cross-neutralizes several poxviruses more efficiently than 7D11, the most potent antibody targeting the EFC described to date. These findings highlight the potential of A16/G9 as a candidate for subunit vaccines and identify regions of the EFC as targets for antiviral development.

Monkeypox virus (MPXV), closely related to variola virus, causes mpox, a zoonotic disease traditionally endemic to Central Africa. However, recent outbreaks have increased human transmission of MPXV clades. In 2022, global MPXV spread was linked to clade IIb, whereas in 2024, the more pathogenic clade Ib became predominant. These trends raised concerns about sustained human transmission, prompting the WHO to declare mpox a Public Health Emergency of International Concern. Despite the availability of smallpox vaccines, their protective efficacy against mpox remains limited. Additionally, the limited efficacy of current smallpox antivirals, such as Tecovirimat and Brincidofovir, alongside growing concerns about the emergency of tecovirimat resistance mutants, underscores the need for new therapeutic options. Given these challenges, novel antiviral strategies with different mechanisms of action are urgently needed to control MPXV outbreaks. Plitidepsin, a cyclodepsipeptide drug initially approved for cancer treatment, has demonstrated potent antiviral activity against multiple viruses by targeting eukaryotic elongation factor 1 alpha (eEF1A). Here, we have evaluated the antiviral activity of plitidepsin against MPXV infection. In cultured cells, plitidepsin exhibited strong antiviral effects, with a favorable therapeutic index and low cytotoxicity. In CAST/EiJ mice, a highly susceptible MPXV model, plitidepsin significantly reduced viral replication in the lungs. Additionally, treated mice displayed a marked reduction in inflammatory lung lesions and proinflammatory cytokines, suggesting immunomodulatory effects. These findings indicate plitidepsin as a promising candidate for mpox treatment. Further studies are needed to explore its potential as a standalone or combination therapy, supporting clinical evaluation for mpox treatment.

Effective vaccination strategies adaptable to emerging viruses like SARS-CoV-2 and capable of inducing robust protective immunity are needed. We evaluated the immunogenicity and protective efficacy of homologous and heterologous prime/boost regimens against SARS-CoV-2 in K18-hACE2 mice and Syrian hamsters using Newcastle disease virus (NDV-HXP-S, intranasal) and modified vaccinia virus Ankara (MVA-S(3P), intramuscular) vectors encoding a prefusion-stabilized SARS-CoV-2 spike (S) protein. All regimens protected against weight loss and markedly reduced viral replication and lung pathology. Vaccination induced serum anti-S and anti-receptor binding domain IgGs and neutralizing antibodies against ancestral virus and variants. In mice, mucosal anti-S IgA and IgG were detected after NDV-HXP-S immunization. Homologous MVA-S(3P)/MVA-S(3P) and heterologous NDV-HXP-S/MVA-S(3P) elicited higher polyfunctional systemic T-cell responses, while homologous NDV-HXP-S/NDV-HXP-S induced stronger pulmonary CD8+ T cells. Hamsters vaccinated with NDV-HXP-S exhibited protection of the upper respiratory tract, with the NDV-HXP-S/MVA-S(3P) regimen showing a trend toward reduced direct contact transmission of SARS-CoV-2. These findings demonstrate the capacity of NDV and MVA vector platforms to induce robust systemic and mucosal antigen-specific humoral and T-cell responses against SARS-CoV-2, contributing to protection against both disease and transmission, and support further exploration of these vector platforms for vaccination against SARS-CoV-2 and potentially other pathogens.

Background: Vaccines represent one of the most affordable and efficient tools for controlling infectious diseases; however, the development of efficacious vaccines against complex pathogens remains a major challenge. Adjuvants play a relevant role in enhancing vaccine-induced immune responses. One such molecule is interferon-stimulated gene 15 (ISG15), a key modulator of antiviral immunity that acts both through ISGylation-dependent mechanisms and as a cytokine-like molecule. Methods: In this study, we assessed the immunostimulatory potential of ISG15 as an adjuvant in Modified Vaccinia virus Ankara (MVA)-based vaccine candidates targeting Zika virus (ZIKV) and Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Early innate responses and immune cell infiltration were analyzed in immunized mice by flow cytometry and cytokine profiling. To elucidate the underlying mechanism of action of ISG15, in vitro co-infection studies were performed in macrophages. Finally, we evaluated the magnitude and functional quality of the elicited antigen-specific cellular immune responses in vivo. Results: Analysis of early innate responses revealed both platform- and variant-specific effects. ISG15AA preferentially promoted natural killer (NK) cell recruitment at the injection site, whereas ISG15GG enhanced myeloid cell infiltration in draining lymph nodes (DLNs), particularly when delivered via MVA. Moreover, in vitro co-infection of macrophages with MVA-based vaccine vectors and the ISG15AA mutant led to a marked increase in proinflammatory cytokine production, highlighting a dominant role for the extracellular, ISGylation-independent functions of ISG15 in shaping vaccine-induced immunity. Notably, co-infection of ISG15 with MVA-ZIKV and MVA-SARS-CoV-2 vaccine candidates enhanced the magnitude of antigen-specific immune responses in both vaccine models. Conclusions: ISG15, particularly in its ISGylation-deficient form, acts as a promising immunomodulatory adjuvant for viral vaccines, enhancing both innate and adaptive immune responses. Consistent with previous findings in the context of Human Immunodeficiency virus type 1 (HIV-1) vaccines, this study further supports the potential of ISG15 as an effective adjuvant for vaccines targeting viral infections such as ZIKV and SARS-CoV-2.

The Interferon Stimulated Gene 15 (ISG15), a unique Ubiquitin-like (Ubl) modifier exclusive to vertebrates, plays a crucial role in the immune system. Primarily induced by interferon (IFN) type I, ISG15 functions through diverse mechanisms: (i) covalent protein modification (ISGylation); (ii) non-covalent intracellular action; and (iii) exerting extracellular cytokine activity. These various roles highlight its versatility in influencing numerous cellular pathways, encompassing DNA damage response, autophagy, antiviral response, and cancer-related processes, among others. The well-established antiviral effects of ISGylation contrast with its intriguing dual role in cancer, exhibiting both suppressive and promoting effects depending on the tumour type. The multifaceted functions of ISG15 extend beyond intracellular processes to extracellular cytokine signalling, influencing immune response, chemotaxis, and anti-tumour effects. Moreover, ISG15 emerges as a promising adjuvant in vaccine development, enhancing immune responses against viral antigens and demonstrating efficacy in cancer models. As a therapeutic target in cancer treatment, ISG15 exhibits a double-edged nature, promoting or suppressing oncogenesis depending on the tumour context. This review aims to contribute to future studies exploring the role of ISG15 in immune modulation and cancer therapy, potentially paving the way for the development of novel therapeutic interventions, vaccine development, and precision medicine.

Vaccines based on mRNA technology have revolutionized the field. In fact, lipid nanoparticles (LNP) formulated with mRNA are the preferential vaccine platform used in the fight against SARS-CoV-2 infection, with wider application against other diseases. The high demand and property right protection of the most potent cationic/ionizable lipids used for LNP formulation of COVID-19 mRNA vaccines have promoted the design of alternative nanocarriers for nucleic acid delivery. In this study we have evaluated the immunogenicity and efficacy of different rationally designed lipid and polymeric-based nanoparticle prototypes against SARS-CoV-2 infection. An mRNA coding for a trimeric soluble form of the receptor binding domain (RBD) of the spike (S) protein from SARS-CoV-2 was encapsulated using different components to form nanoemulsions (NE), nanocapsules (NC) and lipid nanoparticles (LNP). The toxicity and biological activity of these prototypes were evaluated in cultured cells after transfection and in mice following homologous prime/boost immunization. Our findings reveal good levels of RBD protein expression with most of the formulations. In C57BL/6 mice immunized intramuscularly with two doses of formulated RBD-mRNA, the modified lipid nanoparticle (mLNP) and the classical lipid nanoparticle (LNP-1) were the most effective delivery nanocarriers at inducing binding and neutralizing antibodies against SARS-CoV-2. Both prototypes fully protected susceptible K18-hACE2 transgenic mice from morbidity and mortality following a SARS-CoV-2 challenge. These results highlight that modulation of mRNAs immunogenicity can be achieved by using alternative nanocarriers and support further assessment of mLNP and LNP-1 prototypes as delivery vehicles for mRNA vaccines.

Despite the high efficiency of current SARS-CoV-2 mRNA vaccines in reducing COVID-19 morbidity and mortality, waning immunity and the emergence of resistant variants underscore the need for novel vaccination strategies. This study explores a heterologous mRNA/Modified Vaccinia virus Ankara (MVA) prime/boost regimen employing a trimeric form of the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein compared to a homologous MVA/MVA regimen. In C57BL/6 mice, the RBD was delivered during priming via an mRNA vector encapsulated in nanoemulsions (NE) or lipid nanoparticles (LNP), followed by a booster with a replication-deficient MVA-based recombinant virus (MVA-RBD). This heterologous mRNA/MVA regimen elicited strong anti-RBD binding and neutralizing antibodies (BAbs and NAbs) against both the ancestral SARS-CoV-2 strain and different variants of concern (VoCs). Additionally, this protocol induced robust and polyfunctional RBD-specific CD4 and CD8 T cell responses, particularly in animals primed with mLNP-RBD. In K18-hACE2 transgenic mice, the LNP-RBD/MVA combination provided complete protection from morbidity and mortality following a live SARS-CoV-2 challenge compared with the partial protection observed with mNE-RBD/MVA or MVA/MVA regimens. Although the mNE-RBD/MVA regimen only protects half of the animals, it was able to induce antibodies with Fc-mediated effector functions besides NAbs. Moreover, viral replication and viral load in the respiratory tract were markedly reduced and decreased pro-inflammatory cytokine levels were observed. These results support the efficacy of heterologous mRNA/MVA vaccine combinations over homologous MVA/MVA regimen, using alternative nanocarriers that circumvent intellectual property restrictions of current mRNA vaccine formulations.

Despite the decrease in mortality and morbidity due to SARS-CoV-2 infection, the incidence of infections due to Omicron subvariants of SARS-CoV-2 remains high. The mutations acquired by these subvariants, mainly concentrated in the receptor-binding domain (RBD), have caused a shift in infectivity and transmissibility, leading to a loss of effectiveness of the first authorized COVID-19 vaccines, among other reasons, by neutralizing antibody evasion. Hence, the generation of new vaccine candidates adapted to Omicron subvariants is of special interest in an effort to overcome this immune evasion. Here, an optimized COVID-19 vaccine candidate, termed MVA-S(3P_BA.1), was developed using a modified vaccinia virus Ankara (MVA) vector expressing a full-length prefusion-stabilized SARS-CoV-2 spike (S) protein from the Omicron BA.1 variant. The immunogenicity and efficacy induced by MVA-S(3P_BA.1) were evaluated in mice in a head-to-head comparison with the previously generated vaccine candidates MVA-S(3P) and MVA-S(3Pbeta), which express prefusion-stabilized S proteins from Wuhan strain and Beta variant, respectively, and with a bivalent vaccine candidate composed of a combination of MVA-S(3P) and MVA-S(3P_BA.1). The results showed that all four vaccine candidates elicited, after a single intramuscular dose, protection of transgenic K18-hACE2 mice challenged with SARS-CoV-2 Omicron BA.1, reducing viral loads, histopathological lesions, and levels of proinflammatory cytokines in the lungs. They also elicited anti-S IgG and neutralizing antibodies against various Omicron subvariants, with MVA-S(3P_BA.1) and the bivalent vaccine candidate inducing higher titers. Additionally, an intranasal immunization in C57BL/6 mice with all four vaccine candidates induced systemic and mucosal S-specific CD4+ and CD8+ T-cell and humoral immune responses, and the bivalent vaccine candidate induced broader immune responses, eliciting antibodies against the ancestral Wuhan strain and different Omicron subvariants. These results highlight the use of MVA as a potent and adaptable vaccine vector against new emerging SARS-CoV-2 variants, as well as the promising feature of combining multivalent MVA vaccine candidates.

Background: The COVID-19 pandemic, caused by SARS-CoV-2, has highlighted the need for vaccines targeting both neutralizing antibodies (NAbs) and long-lasting cross-reactive T cells covering multiple viral proteins to provide broad and durable protection against emerging variants. Methods: To address this, here we developed two vaccine candidates, namely (i) DNA-CoV2-TMEP, expressing the multiepitopic CoV2-TMEP protein containing immunodominant and conserved T cell regions from SARS-CoV-2 structural proteins, and (ii) MVA-CoV2-B2AT, encoding a bi-cistronic multiepitopic construct that combines conserved B and T cell overlapping regions from SARS-CoV-2 structural proteins. Results: Both candidates were assessed in vitro and in vivo demonstrating their ability to induce robust immune responses. In C57BL/6 mice, DNA-CoV2-TMEP enhanced the recruitment of innate immune cells and stimulated SARS-CoV-2-specific polyfunctional T cells targeting multiple viral proteins. MVA-CoV2-B2AT elicited NAbs against various SARS-CoV-2 variants of concern (VoCs) and reduced viral replication and viral yields against the Beta variant in susceptible K18-hACE2 mice. The combination of MVA-CoV2-B2AT with a mutated ISG15 form as an adjuvant further increased the magnitude, breadth and polyfunctional profile of the response. Conclusion: These findings underscore the potential of these multiepitopic proteins when expressed from DNA or MVA vectors to provide protection against SARS-CoV-2 and its variants, supporting their further development as next-generation COVID-19 vaccines.

The constant appearance of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VoCs) has jeopardized the protective capacity of approved vaccines against coronavirus disease-19 (COVID-19). For this reason, the generation of new vaccine candidates adapted to the emerging VoCs is of special importance. Here, we developed an optimized COVID-19 vaccine candidate using the modified vaccinia virus Ankara (MVA) vector to express a full-length prefusion-stabilized SARS-CoV-2 spike (S) protein, containing 3 proline (3P) substitutions in the S protein derived from the beta (B.1.351) variant, termed MVA-S(3Pbeta). Preclinical evaluation of MVA-S(3Pbeta) in head-to-head comparison to the previously generated MVA-S(3P) vaccine candidate, expressing a full-length prefusion-stabilized Wuhan S protein (with also 3P substitutions), demonstrated that two intramuscular doses of both vaccine candidates fully protected transgenic K18-hACE2 mice from a lethal challenge with SARS-CoV-2 beta variant, reducing mRNA and infectious viral loads in the lungs and in bronchoalveolar lavages, decreasing lung histopathological lesions and levels of proinflammatory cytokines in the lungs. Vaccination also elicited high titers of anti-S Th1-biased IgGs and neutralizing antibodies against ancestral SARS-CoV-2 Wuhan strain and VoCs alpha, beta, gamma, delta, and omicron. In addition, similar systemic and local SARS-CoV-2 S-specific CD4+ and CD8+ T-cell immune responses were elicited by both vaccine candidates after a single intranasal immunization in C57BL/6 mice. These preclinical data support clinical evaluation of MVA-S(3Pbeta) and MVA-S(3P), to explore whether they can diversify and potentially increase recognition and protection of SARS-CoV-2 VoCs.

[This corrects the article DOI: 10.3389/fimmu.2022.1044025.].

The development of new strategies to achieve a functional cure for HIV remains a priority. We tested a novel HIV therapeutic vaccine using unmodified mRNA (TMEP-B) and mRNA modified by 1-methyl-3′-pseudouridylyl (TMEP-Bmod) expressing both a multiepitopic sequences from Gag, Pol, and Nef proteins, including different CD4 and CD8 T-cell epitopes functionally associated with HIV control in transfected monocyte-derived dendritic cells (MDDCs) obtained from HIV infected patients. In vitro assays were used to test the mRNAs alone and in combination with immunomodulator agents, such as the TLR-7 agonist Vesatolimod and the PD-1 antagonist Nivolumab to try to improve HIV-specific cellular immune responses. Combining the mRNAs with the immunomodulators enhanced HIV-specific T-cell responses, together with the secretion of IFNγ, IP10, MIP-1α, and MIP-1β, which are fundamental mediators of viral control. Our data suggest that the mRNA vaccine prototypes TMEP-B and TMEP-Bmod, when combined with Vesatolimod and/or Nivolumab, could achieve functional cure for patients with HIV.

Current vaccines against SARS-CoV-2, based on the original Wuhan sequence, induce antibodies with different degrees of cross-recognition of new viral variants of concern. Despite potent responses generated in vaccinated and infected individuals, the Omicron (B.1.1.529) variant causes breakthrough infections, facilitating viral transmission. We previously reported a vaccine based on a cyclic peptide containing the 446-488 S1 sequence (446-488cc) of the SARS-CoV-2 spike (S) protein from Wuhan isolate. To provide the best immunity against Omicron, here we compared Omicron-specific immunity induced by a Wuhan-based 446-488cc peptide, by a Wuhan-based recombinant receptor-binding domain (RBD) vaccine and by a new 446-488cc peptide vaccine based on the Omicron sequence. Antibodies induced by Wuhan peptide 446-488cc in three murine strains not only recognized the Wuhan and Omicron 446-488 peptides similarly, but also Wuhan and Omicron RBD protein variants. By contrast, antibodies induced by the Wuhan recombinant RBD vaccine showed a much poorer cross-reactivity for the Omicron RBD despite similar recognition of Wuhan and Omicron peptide variants. Finally, although the Omicron-based 446-488cc peptide vaccine was poorly immunogenic in mice due to the loss of T cell epitopes, co-immunization with Omicron peptide 446-488cc and exogenous T cell epitopes induced strong cross-reactive antibodies that neutralized Omicron SARS-CoV-2 virus. Since mutations occurring within this sequence do not alter T cell epitopes in humans, these results indicate the robust immunogenicity of 446-488cc-based peptide vaccines that induce antibodies with a high cross-recognition capacity against Omicron, and suggest that this sequence could be included in future vaccines targeting the Omicron variant.

The development of novel optimized vaccines against coronavirus disease 2019 (COVID-19) that are capable of controlling the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic and the appearance of different variants of concern (VoC) is needed to fully prevent the transmission of the virus. In the present study, we describe the enhanced immunogenicity and efficacy elicited in hamsters by a modified vaccinia virus Ankara (MVA) vector expressing a full-length prefusion-stabilized SARS-CoV-2 spike (S) protein [termed MVA-S(3P)]. Hamsters vaccinated with one or two doses of MVA-S(3P) developed high titers of S-binding IgG antibodies and neutralizing antibodies against the ancestral Wuhan SARS-CoV-2 virus and VoC beta, gamma, and delta, as well as against omicron, although with a somewhat lower neutralization activity. After SARS-CoV-2 challenge, vaccinated hamsters did not lose body weight as compared to matched placebo (MVA-WT) controls. Consistently, vaccinated hamsters exhibited significantly reduced viral RNA in the lungs and nasal washes, and no infectious virus was detected in the lungs in comparison to controls. Furthermore, almost no lung histopathology was detected in MVA-S(3P)-vaccinated hamsters, which also showed significantly reduced levels of proinflammatory cytokines in the lungs compared to unvaccinated hamsters. These results reinforce the use of MVA-S(3P) as a vaccine candidate against COVID-19 in clinical trials.