Use of Highly Pathogenic Avian Influenza A(H5N1) Gain-Of-Function Studies for Molecular-Based Surveillance and Pandemic Preparedness

Davis, C. Todd; Chen, Li-Mei; Pappas, Claudia; Stevens, James; Tumpey, Terrence M.; Gubareva, Larisa V.; Katz, Jacqueline M.; Villanueva, Julie M.; Donis, Ruben O.; Cox, Nancy J.

A recent instance of enhanced surveillance and response by the CDC and regional partners occurred following the abrupt rise in human cases of H5N1 that occurred in Cambodia in 2013. At the same time that increased case numbers were detected, public sequence database mining by researchers identified viruses from several 2013 human infections that possessed the same mutations shown by GOF studies to alter receptor-binding specificity toward an ␣2,6 preference (K189R and Q222L) and enhanced respiratory droplet transmission of a clade 1 virus in ferrets (N220K with Q222L) (42) . Additional amino acid sequence comparisons of these viruses to those of previously circulating Cambodian clade 1 viruses revealed three other HA substitutions conserved in all 2013 viruses. These three mutations were also shown by GOF experiments to increase binding of H5 viruses to mammalian host cell sialic acid receptors in ␣2,6 linkage either alone (S133A and S155N) or in combination with other mutations (S123P) (43) (44) (45) . These sequence findings directly led the CDC to dispatch a team of three subject matter experts to Cambodia to conduct an epidemiological investigation of sources of exposure to poultry for these human cases, case contact trace-back, including serologic analysis for H5 antibody, and retrospective investigations of poultry deaths and outbreaks in locations where cases were discovered. In addition, an intensive effort was undertaken to consolidate and analyze human and animal epidemiological and sequence data through collaboration across public health and veterinary sectors, as well as local, regional, and global agencies (42) . Although comparisons of the viral genomes of poultry and environmental samples to human samples demonstrated that the K189R, N220K, and Q222L mutations (i) were absent in poultry viruses, (ii) were likely to have arisen during human infection, and (iii) did not transmit from person to person, the enhanced surveillance, improved lab-oratory capacity, and financial resources that resulted from this investigation highlight the utility of GOF data for pandemic preparedness (42) . Because of the finding that these GOF mutations likely occurred during replication in humans and the possibility that they might arise again, a candidate vaccine virus (CVV) was developed against A/Cambodia/X0810301/2013, the virus that possessed two of the markers described by Imai et al. as enhancing ferret aerosol transmission and three mutations shown to alter avian receptor-binding specificity (21, 46) . While a vaccine stockpile was not manufactured using this particular CVV, having a vaccine virus available that has been developed for human use and excluded from Select Agent Regulations reduces the time required for vaccine development and testing by at least 1 month, thus enhancing global pandemic preparedness. This reduction in the time required for vaccine development is the basis for the creation of a library of CVVs for emerging influenza pandemic threats, an approach taken by WHO's Global Influenza Surveillance and Response System for many years (46) .