The seasonal flu, or influenza virus,
infects ~5% of adults and 20% of children each year (1). This is a virus that
mutates relatively quickly and therefore requires a new vaccine to be produced
and administered each year. Between flu seasons, scientists will predict how
the flu is going to mutate and will create a new vaccine to try and prepare the
immune system to combat that variant (2). Unfortunately, this process works
better some years than others. Therefore, in this paper, Tseng et al. is
looking to create a more general flu vaccine that will protect against the
flu virus regardless of how it mutates from year to year. This new vaccine
takes the virus and removes its glycosylation sites. Normally, the flu virus
can have different glycosylation sites and the vaccines will specifically prime
the immune system against specific glycosylation patterns. The vaccine being
created is a monoglycosylated flu vaccine made from chicken eggs.
First,
the authors had to show that they could inhibit the glycosylation of the virus
to create the monoglycosylated virus. They tested this by using different egg
concentrations and different amounts of kifunensine. Then they did SDS/PAGE to
analyze the virus and found that the new virus with kifunensine does remove the
glycosylation sites without affecting overall protein composition within the
virus. They also tested to see if the binding ability of the vaccine was
altered after changing the glycosylated virus, and after doing a hemagglutinin
(HA) assay it showed that there is no change in the binding ability of the
viral HA.
 |
| Figure 1. This is figure 2D from the paper and shows that the monoglycosylated virus (X181mg) has the same amount of HA protein as the other virus. This indicates that when the virus is modified, there are no changes to the overall amount of protein present. |
Now
that the virus is created, the authors injected mice with either the
monoglycosylated vaccine, or other commercial vaccines. After vaccinated the
mice, the scientists collected antisera, blood serum which contains the
animal’s antibodies, to study. The mice inoculated with the monoglycosylated
vaccine had the greatest amount of hemagglutinin inhibition when compared to
the other vaccines given. This shows that this vaccine better neutralized the cross-strain
influenza viruses. After looking at the antisera after the vaccine was given,
the scientists injected a lethal virus dose and the animals were monitored for
another 2 weeks to see how effective the vaccines were. The mice vaccinated with the monoglycosylated
vaccine showed more than 70% protection against the cross-strained
viruses. This indicated this vaccine causes improved antibody response and
subsequent protection. Additionally, the mice who received the monoglycosylated
vaccine had fewer viral particles in their lungs and had less weight loss after
viral infection when compared to the mice who received other viruses.
 |
| Figure 2. This figure shows the serum Titer (A, D, G), neutralization (B, E, H), and percent survival (C, F, I) of both the monoglycosylated virus (X-181mg) when compared to other commercial viruses after the mice were injected with one of three viruses. The monoglycosylated virus is the red line and for all three viruses has the highest neutralization percent and survival percent. |
The
scientists then wanted to know more about why this new vaccine was so
effective. They did an ELISA to look at hemagglutinin levels. It was found that
the monoglycosylated virus had more cross-reactive hemagglutinin specific
antibodies and had more splenocytes released. Splenocytes are white blood cells
that consist of many different cell populations that all propagate an immune
response. Therefore, compared to the other vaccines, the monoglycosylated
vaccine caused more stem specific antibodies as well as antibody secreting
splenocytes. Then, to look at whether this vaccine increased the total number
of antibodies they did an ELISA. It showed that the mouse antisera with the
monoglycosylated had more antistem antibodies in the total antibody count than
the other vaccines.
The
last thing the authors looked at is Fc receptor-mediated immune response.
Normally, the main focus when neutralizing a virus is to look at antibody
protection. However, recently there has been a greater push to look at the Fc
receptor mediated antiviral activities. Fc receptors bind to antibodies that
are attached to cells to stimulate phagocytosis. Their last experiment used an
antibody dependent cellular cytotoxicity assay to study this response. The
assay showed that the monoglycosylated antisera had higher Fc immune activity
when compared to the multi glycosylated vaccine. The antibodies produced by the
monoglycosylated virus can therefore be shown to provide broader protection for
the host.
Ultimately,
this experiment shows that this novel vaccine created from eggs where the virus
has the glycosylation sites removed causes improved protection against
influenza virus. This vaccine improves the immune response, increase
antibodies, and provides a more generalized immune response that can target a
variety of flu viruses, not just a single strain. This has the potential to
save money because new vaccines would not need to be created annually.
Additionally, it would save time for both scientists and the general population
to prevent the need for annual vaccinations.
1) Krammer F, Palese P (2015) Advances
in the development of influenza virus vaccines. Nat Rev Drug Discov 14:167–182.
2) Dos Santos G, Neumeier E,
Bekkat-Berkani R (2016) Influenza: Can we cope better with the unpredictable?
Hum Vaccin Immunother 12:699–708
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