Influenza virus, a highly mutable respiratory pathogen, causes significant disease nearly every year. Current vaccines are designed to protect against circulating influenza strains of a given season. However, mismatches between vaccine strains and circulating strains, as well as inferior vaccine effectiveness in immunodeficient populations, represent major obstacles. In an effort to expand the breadth of protection elicited by influenza vaccination, one of the major surface glycoproteins, hemagglutinin (HA), has been modified to develop immunogens that display conserved regions from multiple viruses or elicit a highly polyclonal antibody response to broaden protection. These approaches, which target either the head or the stalk domain of HA, or both domains, have shown promise in recent preclinical and clinical studies. Furthermore, the role of adjuvants in bolstering the robustness of the humoral response has been studied, and their effects on the vaccine-elicited antibody repertoire are currently being investigated. This review will discuss the progress made in the universal influenza vaccine field with respect to influenza A viruses from the perspectives of both antigen and adjuvant, with a focus on the elicitation of broadly neutralizing antibodies.

The computationally optimized broadly reactive antigen (COBRA) approach has previously been used to generate hemagglutinin (HA) immunogens for several influenza subtypes that expand vaccine-elicited antibody breadth. As nearly all individuals have pre-existing immunity to influenza viruses, influenza-specific memory B cells will likely be recalled upon COBRA HA vaccination.We determined the epitope specificity and repertoire characteristics of pre-existing human B cells to H1 COBRA HA antigens. Cross-reactivity between wild type HA and H1 COBRA HA proteins were observed at both the oligoclonal B cell level and for a subset of isolated monoclonal antibodies (mAbs). The mAbs bound five distinct epitopes on the pandemic A/California/04/2009 head and stem domains, and the majority of the mAbs had HAI and neutralizing activity against pandemic H1 strains. Two head-directed mAbs, CA09-26 and CA09-45, had HAI and neutralizing activity against a pre-pandemic H1 strain. One mAb, P1-05, targets the stem region of H1 HA proteins, but does not compete with known stem-targeting H1 mAbs. We determined that mAb P1-05 recognizes a recently discovered membrane proximal epitope on HA, the anchor epitope, and we identified similar mAbs using B cell repertoire sequencing. In addition, the trimerization domain distance from HA was critical to recognition of this epitope by P1-05. Overall, these data indicate that seasonally vaccinated individuals possess a population of functional H1 COBRA HAreactive B cells that target head, central stalk, and anchor epitopes, and demonstrate the importance of structure-based assessment of subunit protein vaccine candidates to ensure accessibility of optimal protein epitopes..

Mumps virus (MuV) caused the most viral meningitis before mass immunization. Unfortunately, MuV has reemerged in the United States in the past several years. MuV is a member of the genus Rubulavirus, in the family Paramyxoviridae, and has a nonsegmented negative-strand RNA genome. The viral RNA-dependent RNA polymerase (vRdRp) of MuV consists of the large protein (L) and the phosphoprotein (P), while the nucleocapsid protein (NP) encapsulates the viral RNA genome. These proteins make up the replication and transcription machinery of MuV. The P protein is phosphorylated by host kinases, and its phosphorylation is important for its function. In this study, we performed a large-scale small interfering RNA (siRNA) screen targeting host kinases that regulated MuV replication. The human kinase ribosomal protein S6 kinase beta-1 (RPS6KB1) was shown to play a role in MuV replication and transcription. We have validated the role of RPS6KB1 in regulating MuV using siRNA knockdown, an inhibitor, and RPS6KB1 knockout cells. We found that MuV grows better in cells lacking RPS6KB1, indicating that it downregulates viral growth. Furthermore, we detected an interaction between the MuV P protein and RPS6KB1, suggesting that RPS6KB1 directly regulates MuV replication and transcription. IMPORTANCE Mumps virus is an important human pathogen. In recent years, MuV has reemerged in the United State, with outbreaks occurring in young adults who have been vaccinated. Our work provides insight into a previously unknown mumps virus-host interaction. RPS6KB1 negatively regulates MuV replication, likely through its interaction with the P protein. Understanding virus-host interactions can lead to novel antiviral drugs and enhanced vaccine production.

Vaccine development for circulating influenza viruses, particularly for the H3N2 subtype, remains challenging due to consistent antigenic drift. Computationally optimized broadly reactive antigen (COBRA) technology has proven effective for broadening influenza hemagglutinin (HA)-elicited antibody responses compared to wild-type immunogens.