(internet site (doi:10.1038/s41541-017-0020-x).. 2 H3 influenza A challenges, while inoculation with anti-influenza B DMAb yields protection against lethal Victoria and Yamagata lineage influenza B morbidity and mortality. Furthermore, these two DMAbs can be delivered coordinately resulting in exceptionally broad protection against both influenza A and B. We demonstrate this protection is similar to that achieved by conventional protein antibody delivery. DMAbs warrant further investigation as a novel immune therapy platform with distinct advantages for sustained immunoprophylaxis against influenza. Introduction Influenza virus infection remains a serious threat to global health and the world economy. Annual influenza epidemics result in a large number of hospitalizations, with an estimated 3C5 million cases of severe disease and approximately 250,000C500,000 deaths globally (http://www.who.int/mediacentre/factsheets/fs211/en), with much higher mortality rates possible during pandemics. Despite substantial innovations in treatment and prevention of influenza, licensed antiviral drugs and vaccines do not eliminate the risk of infection. Prompt treatment with therapeutic antiviral neuraminidase (NA) inhibitors can lower influenza morbidity, but these drugs have a limited therapeutic window and are subject to sporadic resistance.1C3 Active antiviral immunization with prophylactic influenza vaccines has remarkably lowered seasonal influenza morbidity and mortality at the population level. KMT2D AWD 131-138 However, at-risk groups such as infants, the elderly, and otherwise immune-compromised individuals lack optimal adaptive immune responses following vaccination. Furthermore, to counteract the high rate of influenza virus antigenic drift, seasonal vaccines must be re-formulated and re-administered annually at great cost with significant time constraints. Emerging strains of influenza arising from antigenic shift (re-assortment) and cross-species transmission to humans also pose a considerable pandemic threat.4 The limited capacity to develop a new vaccine to meet the immediacy and high demand accompanying a pandemic outbreak highlights the global need for new, broad, cost-effective intervention strategies against influenza.5 Passive immunization utilizing antibody-based approaches is a notable alternative or adjunct therapy for transient protection against influenza.6 Relatively recently, several laboratories have described new classes of influenza-neutralizing monoclonal antibodies that target conserved sites in the hemagglutinin (HA) antigen and cross-react across diverse influenza A or influenza B viruses.7C10 Preclinical studies in mice and ferrets reveal these novel cross-reactive antibodies can effectively prevent and treat severe influenza infection, supporting their further study for antibody immunoprophylaxis or immunotherapy in influenza virus-infected humans. While great strides in antibody delivery are being made, the expense of bioprocessed monoclonal antibodies, as well as current requirements for frequent administration, likely pose limitations for universal adoption of this approach AWD 131-138 and dissemination to global populations. Alternative delivery technologies which co-opt aspects traditionally associated with immunization, such as viral vectored gene therapy, have shown some promise in delivering anti-influenza antibodies in mice,11, 12 but permanence concerns and pre-existing anti-vector serology may limit utility of repeatedly using these viral vectors in humans. A distinct approach to antibody immune therapy which would allow for simplicity of production and lower costs, with high stability AWD 131-138 and ease of deliverability could be advantageous. In this regard, the technology of DNA-encoded protein antigen delivery has specific advantages as demonstrated by recent successes in the DNA vaccine field: plasmid DNA is well-tolerated and non-integrating, it does not require cold-chain distribution, it can be delivered repeatedly, and it is relatively inexpensive to produce.13 However, to date, the ability to produce substantial levels of protein expression systemically from in vivo delivery of plasmid DNA has not been considered feasible. In this study, we describe construction, development, and in vivo delivery of DNA plasmids encoding optimized influenza-specific broadly neutralizing antibodies, FluA and FluB, that target diverse influenza A and influenza B viruses, respectively. Delivery of FluA DMAb and FluB DMAb results in robust in vivo expression of functional antibodies which protect mice against lethal challenge..