Sperm-binding fake egg could be contraceptive or IVF tool

Researchers have created a sperm-binding 'fake egg' that could be used to either select the best sperm for fertility treatment or for contraception.

They hope to use the fake eggs as an alternative method of selecting the best sperm for IVF, which are currently selected on the basis of how they look and move.

'There is a continued need to give people better reproductive choices, both for increasing fertility and avoiding procreation, which are really two sides of the same coin,' said study co-author Dr Jurrien Dean of the National Institutes of Health in Bethesda, Maryland, to The Scientist.

The fake egg is an agarose bead with the sperm-binding peptide ZP2 attached. The researchers had previously found that ZP2 binds sperm to the zona pellucida, which is the outside matrix of an egg after it has been released during ovulation.

As they report in Science Translational Medicine, human sperm that were isolated using the fake egg showed an enhanced ability to bind and penetrate ovulated eggs. The sperm had an improved ability to bind and penetrate the zona pellucida.

'Fertility clinics will find the idea of being able to select sperm for use in assisted conception according to their abilities to bind to these beads interesting,' Professor Allan Pacey from the University of Sheffield, who was not involved in the study, told New Scientist. 'We really do need better methods to do this, as at the moment our abilities to select the best sperm is somewhat arbitrary.'

Currently, sperm are selected for IVF are chosen on the basis of measures of morphology (shape) and motility (movement).

The researchers acknowledged that double-blind clinical trials will be needed to determine whether sperm chosen for IVF with the ZP2 peptide beads are better than those chosen through existing selection procedures. 'These are proof-of-principle experiments,' Dr Dean told New Scientist.

The researchers also described a mouse model in which the fake eggs were inserted into the uterus. The ZP2 peptide beads bound any incoming sperm and prevented them from reaching the mouse's own eggs, thus providing a long-acting method of contraception.