The IRMS laboratory has developed the
technique of single
sperm freezing, an experimental technique that has contributed
significantly to the success of IVF used as treatment for severe male factor
infertility. Before its introduction in 1996, there was no effective procedure
for the efficient cryopreservation (freezing) and post-thaw recovery of
individual or small groups of human sperm.
Because of their microscopic size, sperm are
easily lost during semen specimen processing, conventional cyropreservation
and thawing. As a result, single sperm freezing provides an option in cases
where the male’s sperm count is less than 1,000 and the post-thaw recovery
rate without the procedure is virtually zero.
In developing single sperm freezing, IRMS
Laboratory Director Jacques Cohen, Ph.D. looked to the developing human
embryo, which is protected by a thin, porous membrane called the zona
pellucida. A hollow sphere remains when cellular material is removed from
the zona. Because it can be seen and handled microscopically both before and
after cyropreservation, it is an ideal capsule for freezing individual, or
small groups of sperm cells. A hamster zona also can be used because of their
large size and minimal affinity to bind with human sperm cells.
Single sperm freezing is especially effective in cases involving "severe
male factor" infertility, when a man's sperm count falls below the
normal parameters – two milliliters of semen volume, 20 million sperm cells
per milliliter and 25% motility (movement). When the ejaculate has zero or
fewer than 1,000 sperm cells, surgical procedures - microsurgical
epididymal sperm aspiration (MESA) or testicular
sperm aspiration (TESA) – may be necessary to retrieve enough sperm for
IVF.
Frequently, the search for sperm within tissue samples collected during these
procedures can take between two and seven hours in the laboratory. In some
cases, the optimum time for injecting the oocytes retrieved during an IVF
cycle passes before viable sperm cells are isolated. If MESA and TESA produce
enough sperm for more than one IVF cycle, they can be available without
further surgery as a result of single sperm freezing. Also, because they can
be thawed immediately after oocyte retrieval, the recovered sperm are
available to be used in conjunction with intracytoplasmic
sperm injection (ICSI) while the eggs still have the potential for
fertilization.
Single Sperm Freezing Procedure
A. Secure Zona
|
B. Evacuation
|
C. Empty Zona
|
 |
|
D. Sperm
Injection
|
E. Zona
Cryopreservaton
|
F. Zona Thaw:
Sperm Recovery
|
Each egg is held with a small holding pipette
(a long, thin glass tube). A needle is used to first make a tiny hole in the
zona and then to suction out the cellular material. The available sperm are
isolated and separated from other cellular debris, added to a very small
amount of culture medium and then deposited in a single layer in a petri dish.
Using a microscope, the andrologist isolates and aspirates each sperm into a
small pipette, washing it and depositing it into a clean droplet of medium.
Finally, they are injected into the empty, jelly-like zona, where they are
trapped and frozen using standard freezing technology.
Risks of Single Sperm Freezing
As with other forms of cryopreservation, frozen sperm can be destroyed if
there are unforeseen technical or mechanical failures in the laboratory. Also,
it is still possible for sperm to be lost or they may not survive the
freeze-thaw process. Other physicians and scientists have criticized this
method as the hamster zona, they argue, may be a vector for transmitting
desease. This argument has been presented without scientific basis or
supporting data.
Articles with additional information on
Single Sperm Freezing for Extreme azoospermia can be found in our research
articles page.
