INFLUENZA EVOLUTION: Challenges for diagnosis Jairo A. Méndez-Rico Influenza Team PAHO/WHO, Washington, DC
Overview Every year, influenza infects up to one in five people around the world, and causes up to half a million deaths Human immune system can detect and destroy the virus However, people can catch flu many times throughout their lifetimes
Viral evolution Evolutionary process lead changes generating new viruses, therefore a new infection and a new immune response has to be established Evolution is a natural process that can occur spontaneously However, viruses are pressured to change: Immune response, vaccines, new cell receptors
Viral evolution Genetic punctual mutation aa change Not aa change Same protein Altered protein Deleterious Beneficial
Viral evolution: antigenic drift Genetic punctual mutation aa change Not aa change Same antigen New antigen Well recognized Not recognized
Viral evolution: antigenic drift Genetic punctual mutation aa change Not aa change Same antigen New antigen Antigenic drift Well recognized Not recognized
Viral evolution: influenza Before 2009 A/H1N1 A/H3N2 B/Vic B/Yam Different viruses with different proteins: Same viruses, same proteins, different lineages Hemagglutinin 1 / 3 Neuraminidase 1 / 2 Hemagglutinin Neuraminidase
Viral evolution: influenza Mutations to the HA1 region of the hemagglutinin protein are thought to drive the majority of antigenic drift in the influenza virus How does it affect lab diagnosis? James Stevens and Ian A. Wilson. SSRL Science Highlight - August 2004
Viral evolution: impact for characterization Lab characterization of antigenic phenotype is possible through the hemagglutination assays, based on: Hemagglutination Hemagglutination inhibition
Haemagglutination Science 4 July 1941: Vol. 94 no. 2427 pp. 22-23 it was noted that the red cells of the infected chick agglutinated in the alantoic fluid.
Haemagglutination + = Non agglutinated RBC Influenza virus Haemagglutination Depends of viral HA to bind polysaccharides of RBS membrane
Haemagglutination inhibition J Exp Med 1 January 1942: Vol. 75 pp. 49-64 it was shown that the addition of specific immune serum inhibited the agglutination in the presence of the homologous virus
Haemagglutination inhibition + + Influenza virus Specific antibodies = Y Y Y Y Depends of specific antibodies to bind (opsonize) viral HA Haemagglutination inhibition
The challenge Y Y Y Y Haemagglutination Haemagglutination inhibition Since both process depend on HA, antigenic drift may alter the performance of the assays
The challenges Since the 1990s the receptor-binding characteristics of A(H3N2)have evolved
Faster evolution Bedford et al. elife 2014;3:e01914. DOI: 10.7554/eLife.01914
The challenges Since the 1990s the receptor-binding characteristics of A(H3N2)have evolved Two major consequences: 1. Difficulty for isolation in eggs 2. Progressive reduction in the ability to bind and agglutinate chicken RBC (1990s) and turkey RBC (2000s)
The challenge 1. Difficulty for isolation in eggs -Low egg isolation rates (Limited availability of candidate vaccine viruses) -Selective pressures (egg adaptation mutations)
Categorization in 2 groups: 1. Restriction to sialoglycans 2. Restriction to egg glycans Less prone to undergoing receptor (antigenic) drift
Egg-adapted strain was antigenically distinct from WHO recommended vaccine prototipe
The challenge: reducing the impact on vaccine selection Impact on vaccine selection
The solutions Change the age at which embryonated eggs are inoculated (9-10 days to 13-15 days old) Change the inoculation route (to allantoic cavity) Change the egg incubation T o (from 33 o C to 35 o C) Low egg isolation rates Improved up to 18%
The solutions Utilizing egg/cell paired viruses (routine characterization) Egg adaptation mutations To estimate how differences between the two may alter HI profiles; helps to select the best A(H3N2) candidate vaccine viruses
The challenge 2. Progressive reduction in the ability to bind and agglutinate chicken RBC (1990s) and turkey RBC (2000s) - H3N2 Inadequate sialic acid receptor interactions -Technical difficulties to perform serologic assays (IH)
Decrease in HIA sensitivity Bedford et al. elife 2014;3:e01914. DOI: 10.7554/eLife.01914 Adapted from: Rambaut A. Integrating influenza antigenic dynamics with molecular evolution. Geneva, 2014
The challenge: Improving HI assays Additional limitations: Time consuming Hard to standardize Inter- and Intra-laboratory variability RBCs from different species are used (turkey, guinea pig, human, chicken, horse, goose) RBC lots can be variable Results can be affected by antibody source Interpretation is subjective Low sensitivity to detect antibodies against avian viruses (Stevens J. CDC. Geneva, 2014)
The solutions Alternatives proposed to improve: -Sensitivity -Accuracy -Sample throughput -Reproducibility between labs Bead formats Solid matrices
-Bead formats (surrogate RBC) Purified Synthetic
-Bead formats (surrogate RBC) Very promising results Reproducible Size of the bead is critical Bead stability is variable Beads are affected by buffer Glycan choice
-Solid matrices Glycan coated bead or RBC vesicle Solid phase + synthetic glycans Solid phase + specific Abs Solid phase + viral HA
The solutions Virus or recombinant protein Synthetic sialyl-glycans RBC membrane vesicles RBC membrane fragments Purified proteins with unspecified glycan composition Detection options Fluorescence Chemiluminescence FRET Direct binding
Conclusions Evolution lead changes generating new influenza viruses Mutations of HA protein generate antigenic drift (specially AH3N2) These changes affect the performance of characterization tests Mutations (drift) may be introduced as part of egg-based vaccine production
Conclusions New methods (or improved) have to be designed to assess serologic characterization of A(H3N2) (synthetic carbohydrates, surrogate RBC ) There are several options (ongoing) to improve HA/HAI assays but also several challenges! Keep it simple Sensitivity/reliability/reproducibility Applicable to all subtypes Keeping costs down
Conclusions More studies have to be developed sharing viruses increase the chances of better approaches
GRACIAS!