In 2015, there was a large outbreak of Zika virus (ZIKV) in Brazil. Despite its relatively mild impact on healthy adults, ZIKV infection during pregnancy has been associated with severe birth defects. Currently, there is no ZIKV vaccine available, but several vaccine candidates based on the ZIKV membrane (M) and envelope (Env) structural proteins showed promising results in preclinical and clinical studies. Here, the immunogenicity and protective efficacy of a non-replicating adenoviral vector type 26 (Ad26) that encodes the ZIKV M-Env antigens (Ad26.ZIKV.M-Env) was evaluated in mice and non-human primates (NHP). Ad26.ZIKV.M-Env induced strong and durable cellular and humoral immune responses in preclinical models. Humoral responses were characterized by Env-binding and ZIKV neutralizing antibody responses while cellular responses were characterized by ZIKV reactive CD4+ and CD8+ T cells. Importantly, a single immunization with a very low dose of 4x107 vp of Ad26.ZIKV.M-Env protected mice from ZIKV challenge. In NHP, a single immunization with a typical human dose of 1x1011 vp of Ad26.ZIKV.M-Env also induced Env-binding and ZIKV neutralizing antibodies and Env and M specific cellular immune responses that associated with complete protection against viremia from ZIKV challenge as measured in plasma and other body fluids. Together these data provide the rationale to progress the Ad26.ZIKV.M-Env candidate vaccine to clinical testing.

Bombyx mori densovirus 1 (BmDNV-1), a major pathogen of silkworms, causes significant losses to the silk industry. The structure of the recombinant BmDNV-1 virus-like particle has been determined at 3.1-Å resolution using X-ray crystallography. It is the first near-atomic-resolution structure of a virus-like particle within the genus Iteravirus. The particles consist of 60 copies of the 55-kDa VP3 coat protein. The capsid protein has a ␤-barrel "jelly roll" fold similar to that found in many diverse icosahedral viruses, including archaeal, bacterial, plant, and animal viruses, as well as other parvoviruses. Most of the surface loops have little structural resemblance to other known parvovirus capsid proteins. In contrast to vertebrate parvoviruses, the N-terminal ␤-strand of BmDNV-1 VP3 is positioned relative to the neighboring 2-fold related subunit in a "domain-swapped" conformation, similar to findings for other invertebrate parvoviruses, suggesting domain swapping is an evolutionarily conserved structural feature of the Densovirinae.Parvoviruses are among the smallest viral pathogens. They form nonenveloped icosahedral particles with a maximum diameter of about 280 Å and have single-stranded DNA genomes. The parvovirus family has been divided into two subfamilies, the Parvovirinae, which infect vertebrates, and the Densovirinae, which infect invertebrates. Bombyx mori densovirus 1 (BmDNV-1) belongs to the Densovirinae subfamily (genus Iteravirus) (17) and causes potentially lethal flacherie disease in silkworms (28), thereby posing a major threat to silk production. So far, only CeDNV (from Casphalia extranea), DpDNV (from Dendrolimus punctatus), and BmDNV-1 belong to the genus Iteravirus, whereas BmDNV-2 and -3 have a bipartite genome with a total length of about 12.5 kb and have been excluded from the Parvoviridae and reassigned to a new family (Bidnaviridae) (31).The 5.1-kb genome of BmDNV-1 has two overlapping genes for the nonstructural proteins in its 5Ј half and a single open reading frame (ORF) that encodes the structural viral proteins (VPs) in the 3Ј portion (17). The VPs are translated using probably four of five initiator codons in the ORF by a leaky scanning mechanism, resulting in four coat protein variants (VP1, 74.9 kb; VP2, 64.3 kb; major capsid protein VP3, 54.9 kb; and VP4, 51.6 kb) (17). The N-terminal part of the largest capsid protein, VP1, contains phospholipase A2 activity that is required for successful infection (7,10,11,17,36). Parvoviruses form Tϭ1 icosahedral capsids that are assembled out of 60 nearly identical VP subunits. Each subunit consists of an eight-stranded antiparallel ␤-barrel known as a "jelly roll" fold (1,13,14,18,29,30,(33)(34)(35). The same fold is utilized by the major capsid protein of many other viruses, ranging from archaeal to bacterial, plant, and animal viruses (4, 20, 27). However, parvoviruses have large insertions in loops connecting the ␤-strands (1,13,14,18,29,30,(33)(34)(35). These insertions define the external surface of the virus, creating feature...

For an efficacious vaccine immunogen, influenza hemagglutinin (HA) needs to maintain a stable quaternary structure, which is contrary to the inherently dynamic and metastable nature of class I fusion proteins. In this study, we stabilized HA with three substitutions within its pH-sensitive regions where the refolding starts. An X-ray structure reveals how these substitutions stabilize the intersubunit β-sheet in the base and form an interprotomeric aliphatic layer across the stem while the native prefusion HA fold is retained. The identification of the stabilizing substitutions increases our understanding of how the pH sensitivity is structurally accomplished in HA and possibly other pH-sensitive class I fusion proteins. Our stabilization approach in combination with the occasional back mutation of rare amino acids to consensus results in well-expressing stable trimeric HAs. This repair and stabilization approach, which proves broadly applicable to all tested influenza A HAs of group 1 and 2, will improve the developability of influenza vaccines based on different types of platforms and formats and can potentially improve efficacy.