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Development of a vaccine against HIV remains a major target goal in the field. The recent success of mRNA vaccines against the coronavirus SARS-CoV-2 is pointing out a new era of vaccine designs against pathogens. Here, we have generated two types of mRNA vaccine candidates against HIV-1; one based on unmodified vectors and the other on 1-methyl-3′-pseudouridylyl modified vectors expressing a T cell multiepitopic construct including protective conserved epitopes from HIV-1 Gag, Pol and Nef proteins (referred to as RNA-TMEP and RNA-TMEPmod, respectively) and defined their biological and immunological properties in cultured cells and in mice. In cultured cells, both mRNA vectors expressed the corresponding protein, with higher levels observed in the unmodified mRNA, leading to activated macrophages with differential induction of innate immune molecules. In mice, intranodal administration of the mRNAs induced the activation of specific T cell (CD4 and CD8) responses, and the levels were markedly enhanced after a booster immunization with the poxvirus vector MVA-TMEP expressing the same antigen. This immune activation was maintained even three months later. These findings revealed a potent combined immunization regimen able to enhance the HIV-1-specific immune responses induced by an mRNA vaccine that might be applicable to human vaccination programs with mRNA and MVA vectors., This study was partially supported by grants from the Spanish Ministry of Economy (MINECO) (grants: SAF2015-66193-R, SAF-2017-88089-R, RTI2018-096309-B-I00); the Fondo Europeo para el Desarrollo Regional (FEDER); the SPANISH AIDS Research Network RD16/0025/0002 and RD16/0025/0014-ISCIII-FEDER (RIS); the Fondo de Investigación Sanitaria (FIS) AC16/00051 and PI18/00699; the Instituto de Salud Carlos III (grants: COV20/00214; ICI20/00067) and the CERCA Programme/Generalitat de Catalunya SGR 615 and SGR 653. This manuscript was funded by the European Commission [grant numbers: FP7-HEALTH-2013-INNOVATION-1 602570-2, H2020-SC1- 2016-2017 (H2020-SC1-2016-RTD) Proposal: 731626-HIVACAR].

Centro de Biotecnología y Genómica de Plantas (CBGP), Zika virus (ZIKV) is a mosquito-borne pathogen with public health importance due to the high risk of its mosquito vector dissemination and the severe neurological and teratogenic sequelae associated with infection. Vaccines with broad immune specificity and control against this re-emerging virus are needed. Here, we described that mice immunized with a priming dose of a DNA plasmid mammalian expression vector encoding ZIKV prM-E antigens (DNA-ZIKV) followed by a booster dose of a modified vaccinia virus Ankara (MVA) vector expressing the same prM-E ZIKV antigens (MVA-ZIKV) induced broad, polyfunctional and long-lasting ZIKV-specific CD4+ and CD8+ T-cell immune responses, with high levels of CD4+ T follicular helper cells, together with the induction of neutralizing antibodies. All those immune parameters were significantly stronger in the heterologous DNA-ZIKV/MVA-ZIKV immunization group compared to the homologous prime/boost immunizations regimens. Collectively, these results provided an optimized immunization protocol able to induce high levels of ZIKV-specific T-cell responses, as well as neutralizing antibodies and reinforce the combined use of DNA-based vectors and MVA-ZIKV as promising prophylactic vaccination schedule against ZIKV., This research was supported by MINECO Spanish grants SAF-2013-45232-R and SAF-2017-88089-R (to M.E.) and Grant PID2019-105117RR-C21/AEI/10.13039/501100011033 from Agencia Estatal de Investigación to M.A.M.-A. P.P was supported by a fellowship from the Ministry of Science and Innovation of Spain and this work is part of her Thesis defence., 16 Pág.

It is known that for achieving high affinity antibody responses, vaccines must be optimized for antigen dose/density, and the prime/boost interval should be at least 4 weeks. Similar knowledge is lacking for generating high avidity T‐cell responses. The functional avidity (FA) of T cells, describing responsiveness to peptide, is associated with the quality of effector function and the protective capacity in vivo. Despite its importance, the FA is rarely determined in T‐cell vaccination studies. We addressed the question whether different time intervals for short‐term homologous vaccinations impact the FA of CD8 T‐cell responses. Four‐week instead of 2‐week intervals between priming and boosting with potent subunit vaccines in C57BL/6 mice did not improve FA. Equally, similar FA was observed after vaccination with virus‐like particles displaying low versus high antigen densities. Interestingly, FA was stable in vivo but not in vitro, depending on the antigen dose and the time interval since T‐cell activation, as observed in murine monoclonal T cells. Our findings suggest dynamic in vivo modulation for equal FA. We conclude that low antigen density vaccines or a minimal 4‐week prime/boost interval are not crucial for the T‐cell's FA, in contrast to antibody responses., Vaccination with changes in the prime/boost interval, or antigen density, did not influence the functional avidity (FA) of antigen‐specific CD8 T cells. However, a monoclonal population in vitro showed improved FA over time. These results suggest steady FA regulation in vivo to ensure equal and stable function and efficiency.

The control of smallpox was achieved using live vaccinia virus (VV) vaccine, which successfully eradicated the disease worldwide. As the variola virus no longer exists as a natural infection agent, mass vaccination was discontinued after 1980. However, emergence of smallpox outbreaks caused by accidental or deliberate release of variola virus has stimulated new research for second-generation vaccine development based on attenuated VV strains. Considering the closely related animal poxviruses that also arise as zoonoses, and the increasing number of unvaccinated or immunocompromised people, a safer and more effective vaccine is still required. With this aim, new vectors based on avian poxviruses that cannot replicate in mammals should improve the safety of conventional vaccines, and protect from zoonotic orthopoxvirus diseases, such as cowpox and monkeypox. In this study, DNA and fowlpox (FP) recombinants that expressed the VV L1R, A27L, A33R, and B5R genes were generated (4DNAmix, 4FPmix, respectively) and tested in mice using novel administration routes. Mice were primed with 4DNAmix by electroporation, and boosted with 4FPmix applied intranasally. The lethal VVIHD-J strain was then administered by intranasal challenge. All of the mice receiving 4DNAmix followed by 4FPmix, and 20% of the mice immunized only with 4FPmix, were protected. The induction of specific humoral and cellular immune responses directly correlated with this protection. In particular, higher anti-A27 antibodies and IFNγ-producing T lymphocytes were measured in the blood and spleen of the protected mice, as compared to controls. VVIHD-J neutralizing antibodies in sera from the protected mice suggest that the prime/boost vaccination regimen with 4DNAmix plus 4FPmix may be an effective and safe mode to induce protection against smallpox and poxvirus zoonotic infections. The electroporation/intranasal administration routes contributed to effective immune responses and mouse survival.

After acute hepatitis C virus (HCV) infection, 20% of individuals clear the virus, which is dependent on sustained Th1 CD4+ T lymphocyte–mediated responses together with polyfunctional CD8+ T cells [1–4]. HCV is highly efficient in establishing persistent infections, and the specific T-cell responses are impaired during chronic infection [5–8] due to appearance of escape mutants [4, 9], inhibitory effects exerted by viral proteins [10], or expression of coinhibitory receptors resulting in T-cell exhaustion [11, 12]. One way to prime T cells and/or reactivate impaired T cells is to express HCV antigens under a more “immunogenic” setting than natural infection where massive antigen expression appears in the tolerogenic liver environment. Therapeutic vaccination has been tested with some success in HCV-infected patients showing evidence of T-cell activation [13, 14]. Vectored vaccines tailored to generate robust T-cell immunity have recently reached the clinic. MVATG16643, a modified virus Ankara (MVA)–based vaccine [15], has shown in a phase I trial good safety and the capacity to induce interferon γ (IFN-γ)–producing T cells with significant although transient viral load decrease in chronically infected patients [16]. Used in combination with pegylated (PEG)–interferon α (IFN-α)/ribavirin in a phase II clinical trial, MVATG16643 resulted in a significant early viral response [17]. The DNA vaccine ChronVac-C [18] has also shown the capacity to induce T cells, which had transient effects on viral load in a phase I/IIa trial [19], and it has been suggested that it improves cure rates when given before PEG–IFN-α/ribavirin treatment [19]. The combined use of DNA vaccines with viral vectors in a prime/boost regimen has been proven useful for enhancing response levels in clinical studies [20–22]. Similarly, in vivo electroporation (EP)–mediated delivery of DNA vaccines either as stand-alone or in a prime/boost setting with viral vectors has also served to enhance the development of polyfunctional CD8+ T-cell responses [23, 24]. Here we have performed a proof-of-concept study to define the extent of improvement that could result from a prime/boost approach based on ChronVac-C and MVATG16643—2 individual vaccines currently in the clinic. These 2 vaccine regimens have been optimized extensively individually previously, and we wanted to investigate whether the combination of 2 regimens could confer additional benefits over the individual regimens. This study thus combines for the first time in the HCV setting approaches previously shown individually to enhance immunogenicity (ie, DNA vaccine delivery with in vivo EP and prime/boost using viral vectors). We performed an exhaustive evaluation of this concept in wild-type C57BL/6J and human leucocyte antigen (HLA)–A2 transgenic mice. This strategy was found very potent for the improvement of polyfunctional CD4+ and CD8+ HCV-specific responses and resulted in a significant increase of epitope recognition.

DNA vaccines and recombinant Listeria monocytogenes that express and secrete SIV Gag and Env antigens were combined in a nonhuman primate prime-boost immunogenicity study followed by a challenge with SIV239. We report that recombinant DNA vaccine delivered intramuscularly, and recombinant L. monocytogenes delivered orally each individually have the ability to induce CD8+ and CD4+ T cell immune responses in a nonhuman primate. Four rhesus monkeys were immunized at weeks 0, 4, 8, and 12 with the pCSIVgag and pCSIVenv DNA plasmids and boosted with SIV expressing L. monocytogenes vaccines at weeks 16, 20, and 28. Four rhesus monkeys received only the L. monocytogenes vaccines at weeks 16, 20, and 28. A final group of monkeys served as a control group. Blood samples were taken before vaccination and 2 weeks post each injection and analyzed by ELISPOT for CD4+ and CD8+ T cell responses. Moderate vaccine induced SIV-specific cellular immune responses were observed following immunization with either DNA or L. monocytogenes vectors. However, the SIV antigen-specific immune responses were significantly increased when Rhesus macaques were primed with SIV DNA vaccines and boosted with the SIV expressing L. monocytogenes vectors. In addition, the combined vaccine was able to impact SIV239 viral replication following an intrarectal challenge. This study demonstrates for the first time that oral L. monocytogenes can induce a cellular immune response in a nonhuman primate and is able to enhance the efficacy of a DNA vaccine as well as provide modest protection against SIV239 challenge.