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Previously we have shown that a single dose of recombinant adenovirus serotype 26 (Ad26) vaccine expressing a prefusion stabilized SARS-CoV-2 spike antigen (Ad26.COV2.S) is immunogenic and provides protection in Syrian hamster and non-human primate SARS-CoV-2 infection models. Here, we investigated the immunogenicity, protective efficacy and potential for vaccine-associated enhanced respiratory disease (VAERD) mediated by Ad26.COV2.S in a moderate disease Syrian hamster challenge model, using the currently most prevalent G614 spike SARS-CoV-2 variant. Vaccine doses of 1×109vp and 1×1010vp elicited substantial neutralizing antibodies titers and completely protected over 80% of SARS-CoV-2 inoculated Syrian hamsters from lung infection and pneumonia but not upper respiratory tract infection. A second vaccine dose further increased neutralizing antibody titers which was associated with decreased infectious viral load in the upper respiratory tract after SARS-CoV-2 challenge. Suboptimal non-protective immune responses elicited by low-dose A26.COV2.S vaccination did not exacerbate respiratory disease in SARS-CoV-2-inoculated Syrian hamsters with breakthrough infection. In addition, dosing down the vaccine allowed to establish that binding and neutralizing antibody titers correlate with lower respiratory tract protection probability. Overall, these pre-clinical data confirm efficacy of a 1-dose vaccine regimen with Ad26.COV2.S in this G614 spike SARS-CoV-2 virus variant Syrian hamster model, show the added benefit of a second vaccine dose, and demonstrate that there are no signs of VAERD under conditions of suboptimal immunity.

The TLR5 agonist flagellin is a potent adjuvant and is currently being developed for use in vaccines. The mechanisms that drive flagellin’s activity are influenced by its administration route. Previous studies showed that lung structural cells (especially epithelial cells lining the conducting airways) are pivotal for the efficacy of intranasally administered flagellin-containing vaccines. In this study, we looked at how the airway epithelial cells (AECs) regulate the flagellin-dependent stimulation of Ag-specific CD4+ T cells and the Ab response in mice. Our results demonstrate that after sensing flagellin, AECs trigger the release of GM-CSF in a TLR5-dependent fashion and the doubling of the number of activated type 2 conventional dendritic cells (cDC2s) in draining lymph nodes. Furthermore, the neutralization of GM-CSF reduced cDC2s activation. This resulted in lower of Ag-specific CD4+ T cell count and Ab titers in mice. Our data indicate that during pulmonary immunization, the GM-CSF released by AECs orchestrates the cross-talk between cDC2s and CD4+ T cells and thus drives flagellin’s adjuvant effect.

The blood stage of the malaria parasite life cycle is responsible for all the clinical symptoms of malaria. During the blood stage, Plasmodium merozoites invade and multiply within host red blood cells (RBCs). Here, we review the progress made, challenges faced, and new strategies available for the development of blood stage malaria vaccines. We discuss our current understanding of immune responses against blood stages and the status of clinical development of various blood stage malaria vaccine candidates. We then discuss possible paths forward to develop effective blood stage malaria vaccines. This includes a discussion of protective immune mechanisms that can be elicited to target blood stage parasites, novel delivery systems, immunoassays and animal models to optimize vaccine candidates in preclinical studies, and use of challenge models to get an early readout of vaccine efficacy.

There is an urgent need for the development of potent vaccination regimens that are able to induce specific T and B cell responses against human immunodeficiency virus type 1 (HIV-1). Here, we describe the generation and characterization of a fusion antigen comprised of the HIV-1 envelope GP120 glycoprotein from clade C (GP120C) fused at its C-terminus, with the modified vaccinia virus (VACV) 14K protein (A27L gene) (termed GP120C14K). The design is directed toward improving the immunogenicity of the GP120C protein through its oligomerization facilitated by the fused VACV 14K protein that results in hexamer-like structures. Two different immunogens were generated: a recombinant GP120C14K fusion protein (purified from a stable CHO-K1 cell line) and a recombinant modified vaccinia virus Ankara (MVA) poxvirus vector expressing the GP120C14K fusion protein (termed MVA-GP120C14K). The GP120C14K fusion protein is recognized by broadly neutralizing antibodies (bNAbs) against HIV-1. In a murine model, a heterologous prime/boost immunization regimen with MVA-GP120C14K prime followed by adjuvanted GP120C14K protein boost generated stronger and polyfunctional HIV-1 Env-specific CD8 T cell responses when compared with the delivery of the monomeric GP120C form. Furthermore, the immunization protocol MVA-GP120C14K/GP120C14K elicited higher HIV-1 Env-specific T follicular helper cells, germinal center B cells and antibody responses than monomeric GP120. In addition, a similar MVA-GP120C14K prime/GP120C14K protein boost regimen performed in rabbits triggered high HIV-1-Env-specific IgG binding antibody titers that were capable of neutralizing HIV-1 pseudoviruses. The extent of HIV-1 neutralization was comparable to that elicited by the current standard GP140 SOSIP trimers from clades B and C when immunized as MVA-SOSIP prime/SOSIP protein boost regimen. Overall, the novel fusion antigen and the corresponding immunization scheme provided in this report can therefore be considered as potential vaccine strategies against HIV-1., This investigation was supported by Spanish grants SAF201345232R and SAF-2017-88089R and, in part, by EU H2020 EHVA grant REP-681032-2. This research was also supported by Spanish AIDS Research Network RD16/0025/0014-ISCIII – FEDER

The blood stage of the malaria parasite life cycle is responsible for all the clinical symptoms of malaria. During the blood stage, Plasmodium merozoites invade and multiply within host red blood cells (RBCs). Here, we review the progress made, challenges faced, and new strategies available for the development of blood stage malaria vaccines. We discuss our current understanding of immune responses against blood stages and the status of clinical development of various blood stage malaria vaccine candidates. We then discuss possible paths forward to develop effective blood stage malaria vaccines. This includes a discussion of protective immune mechanisms that can be elicited to target blood stage parasites, novel delivery systems, immunoassays and animal models to optimize vaccine candidates in preclinical studies, and use of challenge models to get an early readout of vaccine efficacy.

Motility is often a pathogenicity determinant of bacteria targeting mucosal tissues. Flagella constitute the machinery that propels bacteria into appropriate niches. Besides motility, the structural component, flagellin, which forms the flagella, targets Toll-like receptor 5 (TLR5) to activate innate immunity. The compartmentalization of flagellin-mediated immunity and the contribution of epithelial cells and dendritic cells in detecting flagellin within luminal and basal sides are highlighted here, respectively. While a direct stimulation of the epithelium mainly results in recruitment of immune cells and production of antimicrobial molecules, TLR5 engagement on parenchymal dendritic cells can contribute to the stimulation of innate lymphocytes such as type 3 innate lymphoid cells, as well as T helper cells. This review, therefore, illustrates how the innate and adaptive immunity to flagellin are differentially regulated by the epithelium and the dendritic cells in response to pathogens that either colonize or invade mucosa. Fil: Vijayan, Aneesh. Centre National de la Recherche Scientifique; Francia Fil: Rumbo, Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Estudios Inmunológicos y Fisiopatológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Estudios Inmunológicos y Fisiopatológicos; Argentina Fil: Carnoy, Christophe. Centre National de la Recherche Scientifique; Francia Fil: Sirard, Jean-Claude. Centre National de la Recherche Scientifique; Francia

Vaccines against the preerythrocytic stages of malaria are appealing because the parasite can be eliminated before disease onset and because they offer the unique possibility of targeting the parasite with both antibodies and T cells. Although the role of CD8 + T cells in preerythrocytic malaria stages is well documented, a highly effective T cell-inducing vaccine remains to be advanced. Here we report the development of a prime-boost immunization regimen with the Plasmodium falciparum circumsporozoite protein (PfCS) fused to the oligomer-forming vaccinia virus A27 protein and a modified vaccinia virus Ankara (MVA) vector expressing PfCS. This protocol induced polyfunctional CD8 + T cells with an effector memory phenotype and high PfCS antibody levels. These immune responses correlated with inhibition of liver-stage parasitemia in 80% and sterile protection in 40% of mice challenged with a transgenic P. berghei parasite line that expressed PfCS. Our findings underscore the potential of T and B cell immunization strategies for improving protective effectiveness against malaria.

Vaccines against the preerythrocytic stages of malaria are appealing because the parasite can be eliminated before disease onset and because they offer the unique possibility of targeting the parasite with both antibodies and T cells. Although the role of CD8+ T cells in preerythrocytic malaria stages is well documented, a highly effective T cell-inducing vaccine remains to be advanced. Here we report the development of a prime-boost immunization regimen with the Plasmodium falciparum circumsporozoite protein (PfCS) fused to the oligomer-forming vaccinia virus A27 protein and a modified vaccinia virus Ankara (MVA) vector expressing PfCS. This protocol induced polyfunctional CD8+ T cells with an effector memory phenotype and high PfCS antibody levels. These immune responses correlated with inhibition of liver-stage parasitemia in 80% and sterile protection in 40% of mice challenged with a transgenic P. berghei parasite line that expressed PfCS. Our findings underscore the potential of T and B cell immunization strategies for improving protective effectiveness against malaria.

In the HIV vaccine field, there is a need to produce highly immunogenic forms of the Env protein with the capacity to trigger broad B and T-cell responses. Here, we report the generation and characterization of a chimeric HIV-1 gp120 protein (termed gp120-14K) by fusing gp120 from clade B with the vaccinia virus (VACV) 14K oligomeric protein (derived from A27L gene). Stable CHO cell lines expressing HIV-1 gp120-14K protein were generated and the protein purified was characterized by size exclusion chromatography, electron microscopy and binding to anti-Env antibodies. These approaches indicate that gp120-14K protein is oligomeric and reacts with a wide spectrum of HIV-1 neutralizing antibodies. Furthermore, in human monocyte-derived dendritic cells (moDCs), gp120-14K protein upregulates the levels of several proinflammatory cytokines and chemokines associated with Th1 innate immune responses (IL-1β, IFN-γ, IL-6, IL-8, IL-12, RANTES). Moreover, we showed in a murine model, that a heterologous prime/boost immunization protocol consisting of a DNA prime with a plasmid expressing gp120-14K protein followed by a boost with MVA-B [a recombinant modified vaccinia virus Ankara (MVA) expressing HIV-1 gp120, Gag, Pol and Nef antigens from clade B], generates stronger, more polyfunctional, and greater effector memory HIV-1-specific CD4+ and CD8+ T-cell immune responses, than immunization with DNA-gp120/MVA-B. The DNA/MVA protocol was superior to immunization with the combination of protein/MVA and the latter was superior to a prime/boost of MVA/MVA or protein/protein. In addition, these immunization protocols enhanced antibody responses against gp120 of the class IgG2a and IgG3, together favoring a Th1 humoral immune response. These results demonstrate that fusing HIV-1 gp120 with VACV 14K forms an oligomeric protein which is highly antigenic as it activates a Th1 innate immune response in human moDCs, and in vaccinated mice triggers polyfunctional HIV-1-specific adaptive and memory T-cell immune responses, as well as humoral responses. This novel HIV-1 gp120-14K immunogen might be considered as an HIV vaccine candidate for broad T and B-cell immune responses.

Development of subunit vaccines for malaria that elicit a strong, long-term memory response is an intensive area of research, with the focus on improving the immunogenicity of a circumsporozoite (CS) protein-based vaccine. In this study, we found that a chimeric protein, formed by fusing vaccinia virus protein 14K (A27) to the CS of Plasmodium yoelii, induces strong effector memory CD8+ T cell responses in addition to high-affinity Abs when used as a priming agent in the absence of any adjuvant, followed by an attenuated vaccinia virus boost expressing CS in murine models. Moreover, priming with the chimeric protein improved the magnitude and polyfunctionality of cytokine-secreting CD8+ T cells. This fusion protein formed oligomers/aggregates that led to activation of STAT-1 and IFN regulatory factor-3 in human macrophages, indicating a type I IFN response, resulting in NO, IL-12, and IL-6 induction. Furthermore, this vaccination regimen inhibited the liver stage development of the parasite, resulting in sterile protection. In summary, we propose a novel approach in designing CS based pre-erythrocytic vaccines against Plasmodium using the adjuvant-like effect of the immunogenic vaccinia virus protein 14K.

With the aim to develop an efficient and cost-effective approach to control malaria, we have generated porcine parvovirus-like particles (PPV-VLPs) carrying the CD8+ T cell epitope (SYVPSAEQI) of the circumsporozoite (CS) protein from Plasmodium yoelii fused to the PPV VP2 capsid protein (PPV-PYCS), and tested in prime/boost protocols with poxvirus vectors for efficacy in a rodent malaria model. As a proof-of concept, we have characterized the anti-CS CD8+ T cell response elicited by these hybrid PPV-VLPs in BALB/c mice after immunizations with the protein PPV-PYCS administered alone or in combination with recombinant vaccinia virus (VACV) vectors from the Western Reserve (WR) and modified virus Ankara (MVA) strains expressing the entire P. yoelii CS protein. The results of different immunization protocols showed that the combination of PPV-PYCS prime/poxvirus boost was highly immunogenic, inducing specific CD8+ T cell responses to CS resulting in 95% reduction in liver stage parasites two days following sporozoite challenge. In contrast, neither the administration of PPV-PYCS alone nor the immunization with the vectors given in the order poxvirus/VLPs was as effective. The immune profile induced by VLPs/MVA boost was associated with polyfunctional and effector memory CD8+ T cell responses. These findings highlight the use of recombinant parvovirus PPV-PYCS particles as priming agents and poxvirus vectors, like MVA, as booster to enhance specific CD8+ T cell responses to Plasmodium antigens and to control infection. These observations are relevant in the design of T cell-inducing vaccines against malaria, This work was supported by SAF-2008-02036 and the Marcelino Botín Foundation (to Dr. Esteban) La Caixa Foundation International PhD Program Fellowship (to Dr. Vijayan)