A US scientist who suggested that attempts to clone primates might never succeed using current technology has created cloned monkey embryos using a newer 'gentle squeeze' technique. Gerald Schatten and his colleagues transferred the embryos into female monkeys, but none of the resulting pregnancies lasted more than a month. The team, based at the University of Pittsburgh, first reported their work at the annual conference of the American Society for Reproductive Medicine (ASRM) in Philadelphia in October. Now, the work will be published in the 11 December issue of the journal Developmental Biology.
In 2003, Schatten's group reported - in the journal Science - that attempts to clone primates, including humans, may never succeed using the technique used to create Dolly the sheep and other cloned mammals. SCNT (somatic cell nuclear transfer) involves removing the genetic information of an unfertilised egg cell, and replacing it with that of a body cell. The researchers found that vital 'spindle' proteins are lost from the egg during the procedure, which mean that the cell's genetic information cannot be passed on correctly when the cell divides. The team created 716 cloned rhesus monkey embryos using this technique, but all had an abnormal number of chromosomes, and failed to grow. At the time, Schatten said: 'I hope this natural obstacle affords us time to make responsible and enforceable legislation to prevent anyone attempting human reproductive cloning'.
However, in February 2004, scientists in South Korea announced their success in creating cloned human embryos. Using a modified version of the nuclear transfer technique, the team, based at Seoul National University, created 30 cloned human embryos. The technique involves gently squeezing out the egg nucleus (which contains its genetic material), rather than sucking it out. This may cause less damage to the egg, or could mean that the crucial spindle proteins are left behind. The researchers extracted stem cells from 20 of the cloned embryos, from which they managed to grow one human embryonic stem cell (ES cell) line. The research was a breakthrough for 'therapeutic cloning' research, which aims to use cloned ES cells to develop tissue-matched cell therapies for a range of different diseases.
Using the Korean team's method, Schatten's team managed to create 135 cloned monkey embryos, using the genetic material from adult skin and cumulus cells, which surround the developing egg in the ovary. The Pittsburgh research team are focusing much of their work on ways to derive ES cells from non-human primates. Such cells could be used as a template for human embryonic stem cell study, they say, and answer many questions about how ES cells work and whether they can be used safely and effectively against disease or injury. Schatten said the team has 'made improvements by adapting some of the Korean methods and have been able to overcome some of the hurdles we were seeing before', adding 'this is a significant step forward and gives us hope for eventually being able to derive embryonic stem cells through therapeutic cloning'.