This article contains a few of opinions on the state
of oocyte cryopreservation, as I see it.
It seems like every embryo and oocyte cryopreservation
paper that has come out in the past 20 years is the same as the
one before. Two
principles of cryopreservation (there are of course many more),
namely intracellular ice formation (IIF) and osmotic effects (OE)
have shown up in, dare I say, every paper on egg and embryo
freezing since these concepts were made popular by Mazur in the
late 60’s and early 70’s.
Certainly Mazur also proposed other concepts and
principles of cryopreservation.
So why aren’t these other ideas mentioned?
The superficial regurgitation has led researchers down a
road that has, in the past 20 years or so, yielded strikingly
similar results time and time again, and has not yielded any
breakthroughs that would allow for near 100% survival of
embryos, not to mention unfertilized oocytes.
With no major advancements, save some of the current
vitrification manuscripts, the field is at a standstill.
Protocols have been tweaked here and there for years with
no substantial progress. Usually
as time goes by, the older literature becomes outdated,
especially if technology is involved, and the reports of the
past few years are the ones with the new advancements and the
ones to focus on, but in the field of cryobiology, it is the
older literature of 20-40 years ago that are the “good”
reports and most current papers are the ones to be forgotten.
If no real progress has been made in 20 years, it is time
to change something, anything!
By contrast, the current literature on vitrification has
brought about a wide array of different protocols.
Due to the fact that we do not know much about
vitrification, investigators have tried all sorts of freezing
and thawing regimes, the use of numerous penetrating and
non-penetrating cryoprotectants (alone or as mixtures), and
various containers (cryo loops, microscope grids, pulled straws,
etc.) to store oocytes or embryos.
This has led to new discoveries and new information.
What we need now is an influx of new ideas and a review
of past methods in order to standardize egg and embryo storage.
I have been working for over 8 years in the field of cryobiology and have
made several interesting observations and alterations to
protocols that have allowed for nearly full recovery of frozen
human oocytes. However,
subsequent development of these eggs has yet to be perfected.
Most of these studies have focused on replacing sodium
with choline in the freezing medium.
To date over 10 babies have been born worldwide using a
choline-based medium to freeze oocytes.
We are currently in the process of several clinical
trials for human oocyte, embryo, and blastocyst
cryopreservation. Stay
tuned for more information regarding these trials.
For
more information regarding cryopreservation or specifically
human oocyte cryopreservation see the special upcoming issue of
Reproductive BioMedicine Online (RBMO).
Due out late 2003 or early 2004.
And stay tuned to the Galileo website for monthly updates
in the field of cryopreservation.
