The nucleotide sequences of the HA and NA of SH1 and AH1 were downloaded from the GISAID Epiflu database (accession numbers EPI439486 and EPI439507, respectively). strains. == 1. Introduction == On March 31, 2013 the Chinese public health authorities reported three cases of laboratory-confirmed human infection with a novel avian-origin influenza A H7N9 computer virus[1]. Two patients in Shanghai and one in the surrounding Anhui province were hospitalised with symptoms of cough, dyspnoea and high fever and developed acute respiratory distress syndrome (ARDS) and pneumonia complications, which proved to be deadly[2]. As of October 25, 2013[3], 137 human cases of influenza A H7N9 contamination were reported to the WHO, including 45 deaths. This is the highest mortality number attributed to H7 infections worldwide to date. Efforts to restrict avian to human transmission were initiated including shutting down large poultry markets throughout the country. Antivirals are currently the only prophylactic and therapeutic options available for human use. Since the novel H7N9 strains are resistant to M2 ion channel blockers[2],[4], neuraminidase inhibitors are recommended as frontline therapeutic by the Chinese Center for Disease Control and Prevention[5]. However, oseltamivir-resistant viruses have been associated with antiviral treatment and poor clinical outcome[6],[7]. The outstanding adaptive ability of the computer virus and the lack of human pre-immunity and of available vaccines underline the necessity of GNF179 rapid steps to be taken and research around the development on human H7 vaccines is usually underway[8],[9],[10],[11],[12],[13],[14]. Here, we assess the efficacy of a single low vaccine dose of influenza A H7 virus-like particles (VLPs) of Avian GNF179 Influenza A (H7N9) computer virus origin to protect against a stringent viral challenge DHCR24 in the mouse model. Two-component influenza virus-like particles, containing HAs from the first H7N9 computer virus isolates (A/Anhui/1/13 or A/Shanghai/1/13, respectively) and the matrix protein (M1) from A/Udorn/307/1972, were produced in theTrichoplusia niinsect cell line High Five (BTI-TN-5B1-4) using the baculovirus expression system. Previous studies conclusively exhibited the potent immune stimulating properties of live baculovirus in vaccine preparations[15],[16]. Hence, in order to keep the by-product in the vaccine formulation, we concentrated the VLPs and residual baculovirus from the culture supernatant by one-step sucrose-cushion purification. Mice received one VLP vaccine dose containing different amounts of HA (3 g, 0.3 g and 0.03 g) and 5 weeks later were challenged with a stringent viral dose (100 mLD50) of the A/Shanghai/1/13 H7N9 strain. Pre-challenge serum was evaluated for the breadth of reactivity and hemagglutination inhibition (HI) activity of the elicited humoral response to divergent H7 HAs, as well as representatives of all group 2 HA subtypes. Even the lowest tested vaccine doses conferred full protection against the stringent viral challenge. In addition, a single vaccination with the H7 VLP vaccine induced serum antibodies that were broadly reactive and HI active against divergent H7 subtyped viruses. We also detected sero-reactivity to heterosubtypic members of the group 2 HAs, such as H15 and H3. == 2. Materials and methods == == 2.1. Insect cells == Sf9 insect cells (ATCC # CRL-1711) were routinely propagated at 27 C in TNM-FH medium (Gemini Bio-Products, West Sacramento, CA) supplemented with 0.1% (v/v) Pluronic 68 (Sigma, St. Louis, MO), 10% (v/v) foetal bovine serum (FBS) (Atlanta Biologicals, Norcross, GA) and PenicillinStreptomycin antibiotic mixture (Life Technologies, Carlsbad, CA). For baculovirus amplification, the medium was switched to 3% (v/v) FBS. BTI-TN-5B1-4 (High Five Vienna Institute of Biotechnology subclone)[17]cells were used for expression of VLPs and GNF179 maintained at 27 C in custom altered serum-free IPL-41 medium (PAN-Biotech GmbH, Aidenbach, Germany) at 27 C as described in[18]supplemented with PenicillinStreptomycin antibiotic mixture. == 2.2. Viruses == Recombinant influenza viruses were generated by reverse genetics as described before[19],[20],[21]. Recombinant A/Puerto Rico/8/34 (PR8) viruses (6:2) were generated that expressed HA.