New sperm-freezing technique dramatically improves viability of frozen sperm, and may allow safe use of sperm from HIV+ men

A new technique for freezing sperm can dramatically increase the viability of frozen sperm. In addition, as the technique does not involve the freezing of seminal plasma, it holds out the possibility of allowing sperm from HIV+ men to be used without the danger of transmitting the virus.

The technique has been developed by a team from Temuco (Chile) and Ulm (Germany), led by Professor Raul Sanchez (La Frontera University, Temuco, CHILE), and is presented at the World Congress of Fertility and Sterility in Munich, Germany.

Currently, sperm is frozen slowly and then stored in liquid nitrogen at –160 °C. This technique allows recovery of around 30 to 40% activity. However the current technique has drawbacks, including loss of motility and vitality, and damage to the membrane

The new technique is called sperm vitrification (egg and embryo vitrification are already in use in fertility clinics). Sperm are centrifuged to remove the plasma components, and then resuspended in a sucrose solution before being plunged into liquid nitrogen to fast-freeze. The vitrified sperm can then be stored either in liquid nitrogen or in an ultra-cold deep freeze at -86ºC. This gives several advantages over the existing method, including a significant increase in motility of the rethawed sperm (77% motility versus 29% using current methods). In addition, it seems that the sperm are less damaged by the vitrification technique.

It means that a higher concentration of viable sperm can be recovered prior to IVF techniques such as ICSI, which will give a greater chance of fertilization.

As a by-product of the technique, the removal of the sperm plasma means that the technique will separate the sperm from many contaminating agents, such as HIV and other viruses, giving HIV+ men the chance to father children without the likelihood of passing on the virus to the mother and child.

Commenting, lead researcher Professor Sanchez said: “This work shows that we can preserve functional sperm via vitrification, which gives a greater chance of success for patients with low sperm counts. Conventional methods only preserves between 3%0 or 40% of the sperm viability, with the new methodology it is closer to 80%.

The other great advantage of this technique is that it can eliminate potential sources of infection such as AIDS or hepatitis b, which are present in seminal plasma. In this process we discard the seminal plasma, with the sperm being vitrified in culture medium. It has the potential to allow HIV+ men to have children without worrying about transmitting the virus”.

Commenting, Professor Ian Cooke of the IFFS said “This looks a very exciting technique, as it is much faster than the conventional slow-freeze procedure. In addition, the prospect of use with HIV+ patients has great potential, although we’d want to confirm the absence of residual HIV in sperm samples before going ahead”.