SummaryRespiratory syncytial virus (RSV) is a worldwide public health concern for which no vaccine is available. Elucidation of the prefusion structure of the RSV F glycoprotein and its identification as the main target of neutralizing antibodies have provided new opportunities for development of an effective vaccine. Here, we describe the structure-based design of a self-assembling protein nanoparticle presenting a prefusion-stabilized variant of the F glycoprotein trimer (DS-Cav1) in a repetitive array on the nanoparticle exterior. The two-component nature of the nanoparticle scaffold enabled the production of highly ordered, monodisperse immunogens that display DS-Cav1 at controllable density. In mice and nonhuman primates, the full-valency nanoparticle immunogen displaying 20 DS-Cav1 trimers induced neutralizing antibody responses ∼10-fold higher than trimeric DS-Cav1. These results motivate continued development of this promising nanoparticle RSV vaccine candidate and establish computationally designed two-component nanoparticles as a robust and customizable platform for structure-based vaccine design.

Global containment of COVID-19 still requires accessible and affordable vaccines for low- and middle-income countries (LMICs). Recently approved vaccines provide needed interventions, albeit at prices that may limit their global access. Subunit vaccines based on recombinant proteins are suited for large-volume microbial manufacturing to yield billions of doses annually, minimizing their manufacturing cost. These types of vaccines are well-established, proven interventions with multiple safe and efficacious commercial examples. Many vaccine candidates of this type for SARS-CoV-2 rely on sequences containing the receptor-binding domain (RBD), which mediates viral entry to cells via ACE2. Here we report an engineered sequence variant of RBD that exhibits high-yield manufacturability, high-affinity binding to ACE2, and enhanced immunogenicity after a single dose in mice compared to the Wuhan-Hu-1 variant used in current vaccines. Antibodies raised against the engineered protein exhibited heterotypic binding to the RBD from two recently reported SARS-CoV-2 variants of concern (501Y.V1/V2). Presentation of the engineered RBD on a designed virus-like particle (VLP) also reduced weight loss in hamsters upon viral challenge.

The characteristics of CD8+ T cells responsible for memory responses are still largely unknown. Particularly, it has not been determined whether different activation thresholds distinguish naive from memory CD8+ T cell populations. In most experimental systems, heterogeneous populations of primed CD8+ T cells can be identified in vivo after immunization. These cells differ in terms of cell cycle status, surface phenotype, and/or effector function. This heterogeneity has made it difficult to assess the activation threshold and the relative role of these subpopulations in memory responses. In this study we have used F5 T cell receptor transgenic mice to generate a homogeneous population of primed CD8+ T cells. In the F5 transgenic mice, peptide injection in vivo leads to activation of most peripheral CD8+ T cells. In vivo BrdU labeling has been used to follow primed T cells over time periods spanning several weeks after peptide immunization. Our results show that the majority of primed CD8+ T cells generated in this system are not cycling and express increased levels of CD44 and Ly6C. These cells remain responsive to secondary peptide challenge in vivo as evidenced by short term upregulation of activation markers such as CD69 and CD44. The activation thresholds of naive and primed CD8+ T cells were compared in vitro. We found that CD8+ T cells from primed mice are activated by peptide concentrations 10–50-fold lower than naive mice. In addition, the kinetics of interleukin 2Rα chain upregulation by primed CD8+ T cells differ from naive CD8+ T cells. These primed hyperresponsive CD8+ T cells might play an important role in the memory response.

The induction of dendritic cell (DC) maturation is critical for the induction of Ag-specific T lymphocyte responses and may be essential for the development of human vaccines relying on T cell immunity. In this study, we have investigated the effects of monophosphoryl lipid A (MPL) on human monocyte-derived DC as well as peripheral blood T cells. Calcium mobilization, mitogen-activated protein kinase activation, and the NF-κB transcription factor were induced after MPL stimulation of DC and required high doses of MPL (100 μg/ml). Maturation parameters such as production of IL-12 and increases in cell surface expression of HLA-DR, CD80, CD86, CD40, and CD83 were observed following DC treatment with MPL. However, lower levels of IL-12 were induced by MPL when compared with lipopolysaccharide. This is likely to be related to differences in the kinetics of extracellular signal-related kinase 1/2 and p-38 phosphorylation induced by both molecules. Although maturation induced by MPL was weaker when compared with lipopolysaccharide, it appeared to be sufficient to support optimal activation of allogeneic naive CD45RA+ T cell and anti-tetanus toxoid CD4 T cells. MPL at low doses (5 μg/ml) had no impact on DC maturation, while its addition to DC-T cell cocultures induced full T cell activation. The observed effect was related to the fact that MPL also acts directly on T cells, likely through their Toll-like receptors, by increasing their intracellular calcium and up-regulating their CD40 ligand expression. Together, these data support a model where MPL enhances T cell responses by having an impact on DC and T cells.

The goal of the Malaria Vaccine Program at the Walter Reed Army Institute of Research (WRAIR) is to develop a licensed multi-antigen, multi-stage vaccine against Plasmodium falciparum able to prevent all symptomatic manifestations of malaria by preventing parasitemia. A secondary goal is to limit disease in vaccinees that do develop malaria. Malaria prevention will be achieved by inducing humoral and cellular immunity against the pre-erythrocytic circumsporozoite protein (CSP) and the liver stage antigen-1 (LSA-1). The strategy to limit disease will target immune responses against one or more blood stage antigens, merozoite surface protein-1 (MSP-1) and apical merozoite antigen-1 (AMA-1). The induction of T-and B-cell memory to achieve a sustained vaccine response may additionally require immunization with an adenovirus vector such as adenovirus serotype 35. RTS,S, a CSP-derived antigen developed by GlaxoSmithKline Biologicals in collaboration with the Walter Reed Army Institute of Research over the past 17 years, is the cornerstone of our program. RTS,S formulated in AS02A (a GSK proprietary formulation) is the only vaccine candidate shown in field trials to prevent malaria and, in one instance, to limit disease severity. Our vaccine development plan requires proof of an individual antigen's efficacy in a Phase 2 laboratory challenge or field trial prior to its integration into an RTS,S-based, multi-antigen vaccine. Progress has been accelerated through extensive partnerships with industrial, D.G. Heppner Jr. et al. / Vaccine 23 (2005) [2243][2244][2245][2246][2247][2248][2249][2250] academic, governmental, and non-governmental organizations. Recent safety, immunogenicity, and efficacy trials in the US and Africa are presented, as well as plans for the development of a multi-antigen vaccine.