Influenza
Influenza viruses are globally important human pathogens infecting up to 500 million people annually, with children and the elderly being the most vulnerable in the population. Global influenza pandemics in 1918, 1957, and 1968 caused millions of deaths, the most severe epidemic in 1918-1919 with an estimated 40 million fatalities worldwide. Though it is not possible to predict when the next pandemic might occur, that it will occur is almost certain. With the recent emergence of highly pathogenic avian influenza (HPAI) strains, the need for understanding the pathogenesis of influenza A, and for developing vaccines and therapeutics, is prescient.

Reverse Genetics
The development of influenza reverse genetics techniques allowing the generation of recombinant influenza viruses from plasmid DNA was a major breakthrough for understanding the molecular basis of influenza virus pathogenicity. These methods opened a window into the molecular biology of influenza viruses and allowed a reverse genetics approach to study viral gene function. This has led to a molecular understanding of a virus-encoded interferon (IFN) antagonist, NS1. Reverse genetics approaches also allow a new approach to study viral hemagglutinin (HA), polymerase (PB1, PB2, PA), and matrix proteins (M1), and are being adapted for design of influenza vaccines.

NS1
By reverse genetics, we are studying the critical biological roles of the influenza non-structural protein NS1 (see also innate immunity). During the replication cycle of influenza A virus in its hosts, influenza NS1 has been shown to perform several important functions. NS1 has the ability to antagonize type I IFN production, inhibiting the expression of IFN-ß and IFN-α genes and thus preventing an antiviral state in the cell. Dr. García-Sastre's studies provided the first description of this phenomenon among negative strand RNA viruses. These studies led to the generation of attenuated influenza viruses containing defined mutations in their IFN antagonist protein that might prove to be optimal live vaccines against influenza.

1918 and Highly Pathogenic Avian Influenza Reverse genetics-based reconstruction of the influenza A strain responsible for the pandemic of 1918-1919 has allowed for studies into the molecular and biological basis of pathogenicity for this devastating virus. The hemagglutinin of the 1918 influenza virus is critical for transmission. Using a reverse genetics approach, we found that transmission between ferrets can be abolished by two amino acid mutations causing a switch in HA-receptor binding from the human a-2,6 to the avian a-2,3 sialic acid. Currently, we are investigating the mechanism of hemagglutinin activation for 1918 influenza virus. We are also adapting these methods for the study of highly pathogenic avian influenza (HPAI) strains of the H5N1 subtype that have recently emerged in Asia, Europe, and Africa. Recent studies have suggested that in addition to the hemagglutinin and NS1, the viral polymerase genes contribute to the virulence of HPAI in humans. We are examining host factor effects on viral polymerase activity and corresponding viral-host protein interactions. We are also establishing a high containment (Biosafety Level 3) facility for development of animal models for influenza pathogenesis, including mouse, guinea pig, and ferret. Through collaboration with researchers at the Centers for Disease Control and Prevention, the National Centre for Foreign Animal Disease (Canada), and Battelle, we work in Biosafety Levels 3 and 4 to study pathogenesis of the 1918 influenza virus in animals; and with members of the Center for Research on Influenza Pathogenesis for study in avian model systems.

T.M. TUMPEY, T.R. MAINES, N. VAN HOEVEN, L. GLASER, A. SOLÓRZANO, C. PAPPAS, N.J. COX, D.E. SWAYNE, P. PALESE, J.M. KATZ & A. GARCÍA-SASTRE: A two-amino acid change in the hemagglutinin of the 1918 influenza virus abolishes transmission. Science, 315, 655-659 (2007).

T.M. TUMPEY, C.F. BASLER, P.V. AGUILAR, H. ZENG, A. SOLORZANO, D.E. SWAYNE, N.J. COX, J.M. KATZ, J.K. TAUBENBERGER, P. PALESE & A. GARCÍA-SASTRE: Characterization of the reconstructed 1918 Spanish influenza pandemic virus. Science, 310, 77-80 (2005). This paper was selected "paper of the year 2005" by Lancet (Lancet, 367, 636, 2006)

J.H. SCHICKLI, A. FLANDORFER, T. NAKAYA, L. MARTINEZ-SOBRIDO, A. GARCÍA-SASTRE & P. PALESE: Plasmid-only rescue of influenza A virus vaccine candidates. Philosophical Transactions of The Royal Society of London B, 356, 1965-1973 (2001).

E. FODOR, L. DEVENISH, O.G. ENGELHARDT, P. PALESE, G.G. BROWNLEE & A. GARCÍA-SASTRE: Rescue of influenza A virus from recombinant DNA. Journal of Virology, 73, 9679-9682 (1999).

S. PLESCHKA, S.R. JASKUNAS, O.G. ENGELHARDT, T. ZÜRCHER, P. PALESE & A. GARCÍA-SASTRE: A plasmid-based reverse genetics system for influenza A virus. Journal of Virology, 70, 4188-4192 (1996).