Build a better chicken?

Transcription

1 Build a better chicken? Generation of transgenic chickens resistant to avian influenza virus. Dr. Laurence Tiley Dept. Clinical Veterinary Medicine University of Cambridge

2 Prevention is better than cure. Domestic chicken is a confirmed bridge for avian influenza to cross to humans. So far we ve been lucky. Avian transgenesis is now feasible Effective inhibition strategies available Time to burn the bridge?

3 Research goals Detailed analysis of the elements of the viral termini involved in polymerase binding, activation and replication. NAIM and SELEX analysis. Apply this knowledge to the rational design of novel antivirals that block polymerase activation. Target influenza virus replication using RNAi, RNA decoys and other antiviral genes (e.g. Mx). Production of influenza resistant transgenic chickens. Tool for studying role of viral genes in pathogenesis. Proof of principle for a method of producing disease resistant livestock. Reduced production losses due to HPAI. Elimination of potential bridge for cross-species transmission to humans.

4 RNAi approaches Efficacy - enough said. Potential problems. Escape mutants. Virus antagonism NS1 may inhibit RNAi Pre-loading RISC may mask this effect. Saturating RISC with one target may lead to other problems (for transgenic, not therapeutic applications)

5 Decoy RNAs Short RNA molecules expressed at high levels that mimic the binding sites for specific RNA binding proteins. Act as competitive inhibitors and prevent the normal function of the proteins concerned.

6 E.g. Influenza virus 5 and 3 termini 5 G 5 A 6 A 4 A 7 U 3 -A 8 G 2 -C 9 A 1 3 U 1 C 2 -G 9 G 3 -C 8 U 4 U 7 U 5 U 6 A 10 A 11 G 12 G 13 G 14 U 15 G 16 I I I U 10 C 11 C 12 C 13 A 14 C 15 I I I Located at the ends of all influenza virus segments. Absolutely conserved across all serotype A sub-types. Bind influenza virus RNA polymerase with high affinity. Regulate the transcriptional and replicational activity of the enzyme. Highly constrained, unlikely to tolerate mutation.

7 Mx Interferon indicible protein Broad range antiviral activity (esp. RNA viruses) Mechanism unknown GTPase /homology to Dynamin / C Leu-zipper. Inhibits transcription and/or replication. Inhibits translocation of nucleocapsids (Thogotovirus) May interact with PB2 and NP Chicken Mx gene is inactive in most varieties of chicken (S631N restores activity) Avian cell lines expressing functional Mx (mouse) are resistant to influenza infection (~4 log 10 reduction)

8 Objectives Identify optimal RNAi target sequences. Conservation Potency Optimise decoys Structural context. Construct delivery vector Lentivirus vectors based on HIV and EIAV Optimise expression context Position in vector genome Avian specific promoters Additional genes (e.g. Mx) Make transgenic chickens Confirm altered susceptibility to influenza virus. In vivo challenge studies.

9 Inhibition of influenza virus replication assay by RNA decoys and RNAi GFP RNAi PA RNAi NP RNAi Decoy 7 Decoy 6 Decoy 5B Decoy 5A Decoy 4 Decoy 3 NP -ve CAT -ve CAT +ve Influenza replication (µg/ml CAT protein)

10 RNA decoys inhibit influenza virus infection R2 Uninfected Infected + Decoy(-) Infected + Decoy(+)

11 Avian transgenesis McGrew, Sherman, Ellard,Lillico,Gilhooley, Kingsman, Mitrophanos and Sang EMBO reports 5:1-6:

12 Tissue distribution McGrew, Sherman, Ellard,Lillico,Gilhooley, Kingsman, Mitrophanos and Sang EMBO reports 5:1-6:

13 Hurdles to overcome Public acceptance In the UK, GMO is a four letter word. Education Case by case basis. Cost benefit analysis Other nations more pragmatic. Partial resistance Sub-clinical disease HPAI LPAI Still a benefit to producers Practicality Loss of genetic diversity Can be applied to multiple breeds. Cost of global adoption Economic driver for large producers. State endorsement for small producers

14 Current state of play Project funded by the BBSRC. First generation decoy and RNAi vectors tested in vitro. Decoys and NP RNAi vectors show significant inhibition in CAT replication assay. Evidence for efficacy of decoys against virus infection in cell culture. Preliminary evidence for efficacy of avian U6 driven decoys in avian cells. Lentivector delivery system Allows efficient production of transgenic chickens Stable expression over at least 2 generations CMV promoter gives good levels of expression in relevant target organs. Lentivectors containing first generation RNAi and decoys are ready to go into birds.

15 Acknowledgements John Lyall Klara Saville Helen Sang Ele Brown Lizzie Grose Stuart Wilson Alan Kingsman (Cambridge) (Cambridge) (Roslin) (Cambridge) (Cambridge) (UMIST) (Oxford Biomedica)