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technologies that would allow process development
scientists to mix and match media
based on the specific characteristics of the
molecule. Dr. Zhu points to an internal case
where GeneLeap Biotech used the Oligo dT
purification platform for mRNA. " For some
of our projects, the mRNA we worked on
was very clean, with a purity profile higher
than 90% after the IVT. Therefore, we applied
The varying impurity
profiles of mRNA from
the IVT step calls on
options in purification
technologies that would
allow process development
scientists to mix and
match media based on the
specific characteristics
of the molecule.
TFF [tangential flow filtration] or SEC [size
exclusion chromatography] to remove the
small amount of remaining impurities, " he
explains. " For other projects, the impurity
profile was more complex and finding a
common purification platform has been
more difficult than we anticipated. Oligo
dT mediated purification often works fine.
For some mRNA variants, though, we found
very strong double-stranded RNA product
impurities, which required a specific polishing
step to separate. That is why a mix-and-match
approach based on the impurity profile
would be ideal to form the final process. More
adapted purification solutions for mRNA, such
as Cytiva's fiber-based Fibro chromatography,
could also offer a potential alternative to help
facilitate purification of mRNA in the future. "
Additional considerations must also be made
based on whether the mRNA is conventional or
self-amplifying, with the latter having a much
bigger structure that creates additional challenges
in the purification step. " mRNA can be
made using the four conventional nucleotides
as well as modified mRNA, where you are using
base analogs to increase the half-life, which
typically means swapping out uridine for pseudo-uridine, "
says Dr. Liddell. " For self-amplifying
mRNA, you are using sequences derived from
certain viruses to generate what is called a
replicon, constructed from four non-structural
proteins coded by the saRNA, which then makes
copies of the transgene protein that the RNA
is coding for.8 It's quite cunning technology
but is at an earlier stage of development. "
Another critical step in mRNA processing is
encapsulation using lipid nanoparticles. The
specialized lipids used for mRNA provide
a delivery system that protects the nucleic | 21


Table of Contents for the Digital Edition of Cytiva_Jan2022_mRNAVaccinesANewEra

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