Toll-like receptor 4 signaling in hematopoietic-lineage cells contributes to the enhanced activity of the human vaccine adjuvant AS01

Development of Mass Spectrometry Imaging on skeletal muscle to characterize the local pro-inflammatory and pro-resolution lipid responses in a vaccination context

Vaccine reactogenicity is well documented at the clinical level but the mechanism involved at the local or systemic level are still poorly understood. Muscular tissue where most vaccines are administered is the first place of interaction between the vaccine formulation and the host's immune cells. So far, this site of vaccine administration is not well documented from a mechanistic standpoint. The study of early molecular events at the injection site is crucial to understand the local response to vaccines. In this paper, we report a standardized workflow, from the injection of vaccine formulations in rabbit muscle, to the analysis by desorption electrospray ionization and histology staining to understand the role of lipids involved in the inflammation and its resolution on striated muscular tissue. The analysis of lipid mediators was optimized at the site of needle insertion to allow the spatial comparison of cellular infiltrates at the injection site. We showed that lipids were distributed across the spatial tissue morphology in a time-dependent manner. The MS imaging applied to vaccinology could pave the way to a better understanding of vaccine reactogenicity and mechanism of action.

Precision Vaccine Development: Cues From Natural Immunity

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.

Nano-adjuvant based on silk fibroin for the delivery of recombinant hepatitis B surface antigen

Nanotechnology has a vital role in vaccine development. Nano-adjuvants, as robust delivery systems, could stimulate immune responses. Using nanoparticles (NPs) in vaccine formulations enhances the target delivery, immunogenicity, and stability of the antigens. Herein, silk fibroin nanoparticles (SFNPs) were used as a nano-adjuvant for delivering recombinant hepatitis B surface antigen (HBsAg). HBsAg was loaded physically and chemically on the surface of SFNPs. The HBsAg-loaded SFNPs had a spherical morphology. The in vitro release studies showed that HBsAg had a continuous and slow release from SFNPs during 56 days. During this time, ∼45.6% and 34.1% HBsAg was released from physical-SFNPs and chemical-SFNPs, respectively. HBsAg-loaded SFNPs were also stable for six months with slight changes in the size, surface charge, and morphology. The results of circular dichroism (CD) and fluorescence spectroscopy indicated that the released HBsAg preserved the native secondary and tertiary structures. The quantitative cellular uptake study also showed that physical-SFNPs were taken up more into J774A.1 macrophage cells than chemical-SFNPs. After 28 and 56 days post-injection, the immunogenicity studies showed that the specific total IgG, IgG1, and IgG2a levels against HBsAg were significantly higher in the physically loaded group than in the chemically loaded group and commercial hepatitis B vaccine. IgG2a levels were detected only in mice immunized with physical-SFNPs. However, the low levels of IL-4 and IFN-γ were produced in all vaccinated groups and differences in mean values were not significant compared with control groups. Results indicated an improvement in the levels of anti-HBsAg IgG in mice immunized with the physical-SFNPs group compared to other groups.

CCR2- and Flt3-Dependent Inflammatory Conventional Type 2 Dendritic Cells Are Necessary for the Induction of Adaptive Immunity by the Human Vaccine Adjuvant System AS01

The Adjuvant System AS01 contains monophosphoryl lipid A (MPL) and the saponin QS-21 in a liposomal formulation. AS01 is included in recently developed vaccines against malaria and varicella zoster virus. Like for many other adjuvants, induction of adaptive immunity by AS01 is highly dependent on the ability to recruit and activate dendritic cells (DCs) that migrate to the draining lymph node for T and B cell stimulation. The objective of this study was to more precisely address the contribution of the different conventional (cDC) and monocyte-derived DC (MC) subsets in the orchestration of the adaptive immune response after immunization with AS01 adjuvanted vaccine. The combination of MPL and QS-21 in AS01 induced strong recruitment of CD26+XCR1+ cDC1s, CD26+CD172+ cDC2s and a recently defined CCR2-dependent CD64-expressing inflammatory cDC2 (inf-cDC2) subset to the draining lymph node compared to antigen alone, while CD26-CD64+CD88+ MCs were barely detectable. At 24 h post-vaccination, cDC2s and inf-cDC2s were superior amongst the different subsets in priming antigen-specific CD4+ T cells, while simultaneously presenting antigen to CD8+ T cells. Diphtheria toxin (DT) mediated depletion of all DCs prior to vaccination completely abolished adaptive immune responses, while depletion 24 h after vaccination mainly affected CD8+ T cell responses. Vaccinated mice lacking Flt3 or the chemokine receptor CCR2 showed a marked deficit in inf-cDC2 recruitment and failed to raise proper antibody and T cell responses. Thus, the adjuvant activity of AS01 is associated with the potent activation of subsets of cDC2s, including the newly described inf-cDC2s.

The GM-CSF Released by Airway Epithelial Cells Orchestrates the Mucosal Adjuvant Activity of Flagellin

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.