Dr. Jay Calvert - Viral genetics and application to vaccine development
Download as PPTX, PDF1 like284 views
This document discusses the role of viral genetics in the development and efficacy of modified live vaccines (MLVs) for porcine reproductive and respiratory syndrome (PRRS). It highlights the importance of selecting appropriate parental strains, the attenuation process, and factors influencing vaccine efficacy. The document concludes that MLVs remain the most effective tool for PRRS control, with an emphasis on leveraging older ancestral strains for maximum cross-protection.
Dr. Jay Calvert - Viral genetics and application to vaccine development
- 1. 1 VIRAL GENETICS AND APPLICATION TO VACCINE DEVELOPMENT JAY G CALVERT, RESEARCH DIRECTOR, GLOBAL BIOLOGICALS RESEARCH, VMRD, ZOETIS, KALAMAZOO, MI NORTH AMERICAN PRRS SYMPOSIUM DECEMBER 1-3, 2017 CHICAGO, IL
- 2. 2 OVERVIEW OF TODAY’S TALK INTRO TO CONVENTIONAL MODIFIED LIVE VACCINES THE ROLES OF VIRAL GENETICS IN VACCINE EFFICACY SELECTING AN APPROPRIATE STARTING STRAIN THE ATTENUATION PROCESS (PREMEDITATED SERENDIPITY) SUMMARY 1 2 3 4 5
- 3. INTRODUCTION TO CONVENTIONAL MODIFIED LIVE PRRS VACCINES
- 4. 4 More than a dozen conventional PRRS MLV vaccines are commercially licensed: CONVENTIONAL MODIFIED LIVE VIRUS (CELL CULTURE ATTENUATED) VACCINES USA Europe China ROW Ingelvac® PRRS MLV/ RespPRRS® (BIVI) Porcilis® PRRS (MSD) JXA1-R PRRS Vaccine VP-046 BIS (Philippines) Ingelvac® PRRS ATP (BIVI) Unistrain® / Amervac® PRRS (Hipra) TJM-F92 Rui Lan An® (Zoetis joint-venture) Kaketsuken (Japan) PrimePac® PRRS + PrimePac® PRRS RS (Merck) Pyrsvac-183® (Syva) HuN4-F112 BSL-PS 100 (Singapore) Fostera® PRRS (Zoetis) Ingelvac PRRSFLEX® EU & Ingelvac ReproCyc® PRRS EU (BIVI) GDr180 Fostera® PRRS is currently licensed in Canada, Mexico, Philippines, Malaysia, South Korea, Thailand, and Japan Suvaxyn® PRRS MLV (Zoetis) (Market Authorization Sep. 2017) CH-1R R98
- 5. 5 • Commercial MLV PRRS vaccines are the best solution we currently have, and are far more efficacious than killed vaccines or experimental subunit vaccines • MLVs mimic natural infection, which induces very robust protection against the homologous PRRSV strain, including “sterilizing immunity” in some cases • MLVs induce innate immunity (Natural Killer cells and interferon), as well as acquired immunity including T-helper cells (cytokine help), cytotoxic T-cells (killing of infected cells), and B-cells (production of neutralizing antibodies) • MLVs are self-adjuvanting, can be delivered intramuscularly, and only need a single dose for lifetime protection in feeder pigs (customer convenience) CONVENTIONAL MODIFIED LIVE VIRUS (CELL CULTURE ATTENUATED) VACCINES - BENEFITS
- 6. THE ROLES OF VIRAL GENETICS IN VACCINE EFFICACY
- 7. 7 Under control of the vaccine designer Not under control of the vaccine designer Selection of parental virus strain (starting genetics) Genetics, health status, and nutrition of vaccinated animals Attenuation method and endpoint (final vaccine genetics) Immunological history of the herd Formulation Environmental conditions Label recommendations (storage, size and number of doses, route of administration, age at vaccination, etc.) Actual usage of the vaccine (storage, size and number of doses, route of administration, age at vaccination, etc.) Genetics, virulence, and immunogenicity of the challenge virus(es). Co-infections with other pathogens during vaccination and/or challenge. FACTORS THAT INFLUENCE VACCINE EFFICACY
- 9. 9 • Selection of an appropriate parental field strain to become the vaccine is critically important, and must happen before attenuation can begin • It can take 5-7 years to advance from strain selection to licensed vaccine product • Using the most recent “hot” strain as the parent of a new vaccine is a risky strategy • New variants appear and disappear frequently • They don’t always leave economically important descendants after 5-7 years • Recent strains may offer relatively poor cross-protection against other recent, but distantly related, field strains TIMING
- 10. 10 Canine Parvovirus • Example of “linear” (stepwise) evolution • Ancestral strains may be replaced by newer strains • Overall diversity increases slowly • Vaccine update decisions are relatively simple DIFFERENT PATTERNS OF VIRUS EVOLUTION
- 11. 11 PRRS virus • Example of “radial” (multi- directional) evolution • Ancestral strains persist and give rise to many discrete new branches • Over all diversity increases exponentially • Vaccine update decisions are very complex DIFFERENT PATTERNS OF VIRUS EVOLUTION From: Dr. Mike Murtaugh - PRRS '174' - What are we learning about PRRSV evolution and characterization of new emerging strains of PRRSV?
- 12. 12 GENETIC RELATEDNESS Nucleotide Substitution per 100 residues 0 33.8 51015202530 ORF5_Amervac ORF5_Olot_91 ORF5_Porcilis ORF5_Lelystad ORF5_Ingelvac PRRSFLEX EU ORF5_Suvaxyn PRRS MLV ORF5_BEL13-13V117 ORF5_GER09-613 ORF5_AUT15-Acro ORF5_Lena ORF5_VR2332 Mean=86.9% Mean=85.4% …to divergent recent field strains may be maximized by using vaccines based on older (ancestral) strains
- 13. 13 Yes and No. It’s a complex issue! • YES. Obviously some degree of genetic relatedness is required for cross-protection • This is because acquired immunity is based on shared epitopes (B, Tcytotoxic, Thelper) • Homologous protection in PRRSV (100% aa identity, 100% shared epitopes) is uniformly very good. • Heterologous protection within PRRS-1 or PRRS-2 (80-99% aa identity, 11-90% shared epitopes) is variable, and ranges from very good to poor (but usually detectable). • Heterologous protection between PRRS-1 and PRRS-2 (60% aa identify, 1% shared epitopes) is only fair or poor (but detectable with proper study design). • Heterologous protection between distantly related Nidoviruses such as PRRSV and PEDV (<40% aa identity, <<1% shared epitopes) is negligible/ undetectable. DOES GENETIC SIMILARITY PREDICT CROSS- PROTECTION?
- 14. 14 Yes and No. It’s a complex issue! • NO. Factors other than genetic similarity/shared epitopes confound predictions. • The immunogenicity of the first virus is dependent on: • Ability to replicate to high titer (antigenic load) • Ability to induce potent innate and acquired immune responses • Relatively little viral interference with host function (low level of immune dysfunction) • Health and genetics of the host animal • Lack of interfering co-infections • The severity of disease induced by the second virus is dependent on: • Challenge dose and timing • Inherent virulence of the virus • Immune evasion / immune dysfunction mechanisms • Age, health, and genetics of the host animal • Co-infections with other pathogens When existing vaccine options are more closely related to each other than they are to the challenge strain (often the case), the small differences in ORF5 sequence identity are useless for vaccine selection. DOES GENETIC SIMILARITY PREDICT CROSS- PROTECTION?
- 15. 15 • Green trend line added to approximate contribution of genetic relatedness. • Highly Pathogenic Asian PRRS may be below the trend line due to remarkably high virulence. J.G. Calvert, J. Angulo, J.R.D. Allison, B. O'Brien, R.G. Ankenbauer (2015) FOSTERA® PRRS VACCINE HELPS PROVIDE HETEROLOGOUS CROSS- PROTECTION AGAINST A WIDE RANGE OF DIVERSE PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (PRRS) VIRUSES
- 17. 17 • Field strains are very efficacious – but not safe. • The field strain is passaged many times in a cell culture system, resulting in: • Rapid selection for mutations in the virus that confer adaptation (fast growth) in the new cell type (and often reduced growth in the natural cell type) • Gradual accumulation of mutations in viral genes that defend the virus from the immune system, since there is an absence of selection for these functions in cell culture. • Periodically the virus is checked for safety (attenuation of disease) and efficacy. At different passage levels the virus may be: • Under-attenuated (still efficacious, but still not safe enough). Needs more passages! • Over-attenuated (very safe, but no longer efficacious because it can’t grow well in the host animal). Too many passages! • Appropriately-attenuated (safe, and still efficacious). This is a vaccine candidate! On a given attenuation attempt, the window of opportunity may be large or small or even negative in size. You can’t predict which random mutations will appear, and in what order. HOW DOES ATTENUATION WORK?
- 18. 18 SCREENING FOR VACCINE CANDIDATES Expansion on PAM Adaptation to BHK21-C12-26 Cloning X 3 Further adaptation Increase titers Further attenuation Safety & Efficacy in young pigs Unsafe Not efficacious Low titer Candidate ! Candidate ! Not efficacious Not efficacious Low titer
- 19. 19 • Multiple parallel attenuations are recommended, since every attempt yields a different result. • However, careful selection of the starting virus strain and the cell line(s) used for attenuation can limit the spectrum of possible outcomes, and work in your favor. • To the best of our knowledge, all commercially licensed live PRRS vaccines (except two) were attenuated on a particular monkey kidney cell line, MA-104, or cell lines derived from MA-104. • We now know why MA-104 and derivative cell lines like MARC-145 were unique among common cell lines in their ability to grow (some) PRRS viruses • Due to a rare mutation, MA-104 cells unexpectedly express the CD163 protein, which is the primary receptor for all PRRS viruses (discovered at Zoetis in 2004). CD163 is normally expressed on the surface of alveolar macrophages. • What are the exceptions? Which are the only two commercially licensed live PRRS vaccines not attenuated on this monkey kidney cell line? HOW DOES ATTENUATION WORK?
- 20. 20 FOSTERA® PRRS AND SUVAXYN ® PRRS MLV ARE ATTENUATED ON NOVEL ENGINEERED CELL LINES EXPRESSING PORCINE CD163
- 21. 21 TWO ATTENUATION METHODS IN USE TODAY Attenuation on monkey kidney cells expressing monkey CD163 Attenuation on (non-monkey) cells expressing porcine CD163 Examples: More than a dozen commercial PRRS vaccines globally Examples: (1) Fostera® PRRS (2) Suvaxyn® PRRS MLV Attenuation phenotype: Strong selective pressure for the virus to adapt to better recognize monkey CD163. Partial loss of affinity for porcine CD163. Attenuation phenotype: No need for the virus to adapt to a different CD163. Safety achieved by accumulation of mutations in other genes. In the vaccinated pig: Strong selective pressure for the virus to adapt back to better recognize porcine CD163. In the vaccinated pig: No need for the virus to adapt to a different CD163. Stable attenuation phenotype. Label Claims: None of these vaccines has earned a claim for use in nursing pigs as young as 1 day of age. Label Claims: Both have demonstrated safety and efficacy in 1 day old nursing pigs, earning the corresponding USDA/EMA label claims.
- 22. SUMMARY
- 23. 23 • For now, modified live vaccines are by far the most effective tools we have for PRRS control. • It is not cost-effective (or necessary) to attempt to develop and register a new commercial MLV from each new virulent field strain. The process takes 5-7 years and costs millions of dollars. • Because of the radial pattern of PRRSV evolution, maximum cross-protection may be provided using older ancestral strains. • At a high level, there is a clear relationship between the degree of genetic homology between two viruses and their ability to cross-protect against each other. This is a consequence of the number of shared (conserved) antigenic epitopes. • At the ground level, using ORF5 sequences to compare a current field strain to a limited number of vaccine strains, none of which closely resembles the field strain, is fruitless. There are too many other factors in play that confound the genetic predictions of cross-protection. CONCLUSIONS I
- 24. 24 • Attenuation of virulence is accomplished by serial passage on a permissive cell line, leading to increased safety and manufacturability, while maintaining immunogenicity. • The attenuation process is generally stopped when the vaccine has become safe enough to pass standard tests. Additional cell passages risk loss of efficacy (over-attenuation). • Although the random accumulation of mutations during attenuation is unpredictable, strong selection pressures imposed by using different cell lines can influence the spectrum of possible outcomes. In some cases, the “safety stop” is predictable. • An alternative to monkey cell attenuation now exists, which does not require the vaccine virus to adapt to prefer monkey CD163 over porcine CD163. Such vaccines have novel properties, including enhanced safety and efficacy in pre-weaning pigs as young as one day old. CONCLUSIONS II
- 25. THANK YOU FOR YOUR ATTENTION QUESTIONS?