A general computational design strategy for stabilizing viral class I fusion proteins.

Many pathogenic viruses rely on class I fusion proteins to fuse their viral membrane with the host cell membrane. To drive the fusion process, class I fusion proteins undergo an irreversible conformational change from a metastable prefusion state to an energetically more stable postfusion state. Mounting evidence underscores that antibodies targeting the prefusion conformation are the most potent, making it a compelling vaccine candidate. Here, we establish a computational design protocol that stabilizes the prefusion state while destabilizing the postfusion conformation. With this protocol, we stabilize the fusion proteins of the RSV, hMPV, and SARS-CoV-2 viruses, testing fewer than a handful of designs. The solved structures of these designed proteins from all three viruses evidence the atomic accuracy of our approach. Furthermore, the humoral response of the redesigned RSV F protein compares to that of the recently approved vaccine in a mouse model. While the parallel design of two conformations allows the identification of energetically sub-optimal positions for one conformation, our protocol also reveals diverse molecular strategies for stabilization. Given the clinical significance of viruses using class I fusion proteins, our algorithm can substantially contribute to vaccine development by reducing the time and resources needed to optimize these immunogens.

Influenza A Virus Hemagglutinin and Other Pathogen Glycoprotein Interactions with NK Cell Natural Cytotoxicity Receptors NKp46, NKp44, and NKp30.

Natural killer (NK) cells are part of the innate immunity repertoire, and function in the recognition and destruction of tumorigenic and pathogen-infected cells. Engagement of NK cell activating receptors can lead to functional activation of NK cells, resulting in lysis of target cells. NK cell activating receptors specific for non-major histocompatibility complex ligands are NKp46, NKp44, NKp30, NKG2D, and CD16 (also known as FcγRIII). The natural cytotoxicity receptors (NCRs), NKp46, NKp44, and NKp30, have been implicated in functional activation of NK cells following influenza virus infection via binding with influenza virus hemagglutinin (HA). In this review we describe NK cell and influenza A virus biology, and the interactions of influenza A virus HA and other pathogen lectins with NK cell natural cytotoxicity receptors (NCRs). We review concepts which intersect viral immunology, traditional virology and glycobiology to provide insights into the interactions between influenza virus HA and the NCRs. Furthermore, we provide expert opinion on future directions that would provide insights into currently unanswered questions.

Polymerase discordance in novel swine influenza H3N2v constellations is tolerated in swine but not human respiratory epithelial cells.

Swine-origin H3N2v, a variant of H3N2 influenza virus, is a concern for novel reassortment with circulating pandemic H1N1 influenza virus (H1N1pdm09) in swine because this can lead to the emergence of a novel pandemic virus. In this study, the reassortment prevalence of H3N2v with H1N1pdm09 was determined in swine cells. Reassortants evaluated showed that the H1N1pdm09 polymerase (PA) segment occurred within swine H3N2 with ∼ 80% frequency. The swine H3N2-human H1N1pdm09 PA reassortant (swH3N2-huPA) showed enhanced replication in swine cells, and was the dominant gene constellation. Ferrets infected with swH3N2-huPA had increased lung pathogenicity compared to parent viruses; however, swH3N2-huPA replication in normal human bronchoepithelial cells was attenuated - a feature linked to expression of IFN-ß and IFN-λ genes in human but not swine cells. These findings indicate that emergence of novel H3N2v influenza constellations require more than changes in the viral polymerase complex to overcome barriers to cross-species transmission. Additionally, these findings reveal that while the ferret model is highly informative for influenza studies, slight differences in pathogenicity may not necessarily be indicative of human outcomes after infection.

Adenovirus 36, adiposity, and bone strength in late-adolescent females.

Adenovirus 36 (Ad36) is the only adenovirus to date that has been linked with obesity in humans. Our previous studies in late-adolescent females suggest that excess weight in the form of fat mass is associated with lower cortical bone strength. The purpose of this study was to assess the relationship between Ad36-specific antibodies, adiposity, and bone strength in our sample of late-adolescent females. A cross-sectional study of 115 females aged 18 to 19 years was performed. Participants were classified according to adiposity by dual-energy X-ray absorptiometry (body fat percentage as normal-fat [ < 32% body fat; n = 93] or high-fat [ ≥ 32% body fat; n = 22]), and according to the presence of Ad36-specific neutralizing antibodies. Peripheral quantitative computed tomography measured bone parameters at the 4% (trabecular bone) and 20% (cortical bone) site, and muscle cross-sectional area (MCSA) at the 66% site, from the distal metaphyses of the radius and the tibia. Bone strength was determined from volumetric bone mineral density and bone geometry to calculate bone strength index (BSI; trabecular site) and polar strength-strain index (SSI; cortical site). After adjustment for MCSA and limb length, radial SSI was lower in Ad36+ versus Ad36- subjects from the high-fat group (p < 0.03), but not the normal-fat group. No significant differences were observed between groups in tibial SSI or BSI. These data support an association of adiposity and cortical bone strength at the radius with the presence of neutralizing antibodies to Ad36 in late-adolescent females.