The fertility clinic that provided the oocytes from which Dr Andrew French created the world's first authentic cloned human blastocysts by somatic cell nuclear transfer (SCNT) is just over three metres away, on the other side of the wall in his California laboratory.

Those three metres, and a few precious minutes, may have measured the difference between French's success and the failures that have frustrated the best efforts of stem cell researchers around the world to create individualised embryonic stem cells (ESCs) by SCNT, for therapeutic applications and research.

In January, French's team at private stem-cell company Stemagen, in La Jolla, announced in the on-line version of Stem Cell Express that it has achieved a feat that has eluded some of the world's leading stem cell researchers for at least half a decade.

The Australian stem cell scientist's team inserted the nucleus of a diploid somatic cell into an oocyte stripped of its nucleus, then induced it to divide parthogenetically to form a blastocyst - the precursor to a human embryo.

The tiny, berry-like clusters of undifferentiated cells wrap around a core of totipotent embryonic stem cells that have the capacity to differentiate into new ESCs, or any one of the 210-odd specialised cell types that form the human body.

Why did Stemagen succeed, where others had failed?

French believes his team's ready access to oocytes from highly fertile young women may have been an important factor, but also says the team had painstakingly refined its techniques through each iteration. He says they paid particular attention to removing the complete contents of the original haploid nuclei in each oocyte, to ensure there were no chromosome fragments to interfere with the replication of the donor nucleus.

Their meticulous approach worked: five SCNT-derived blastocysts from only 27 oocytes is an unprecedented success rate in a field notorious for meagre success and a very high oocyte wastage rate.

Stemagen recruited its Australian chief scientific officer from Monash University's Centre for Reproduction and Development, where he led a research program to develop transgenic cattle, and transgenic animals for laboratory research. He maintains close links with the centre.

French's team produced five SCNT-derived blastocysts over a period of about eight months, and each time had to make what he describes as a "heartbreaking" decision to hand the blastocysts over to an independent company to carry out genetic tests to provide absolute proof that they carried the somatic cell donor's genes.

"It was a fairly long and involved process, because it involved a number of independent groups looking at the data to [show] we have indeed produced clonal blastocysts," French says. "As each result came out, we became more convinced that we were seeing the real thing - it was a very exciting time.

"The SCNT field for human embryos has had some setbacks, and we had to be very clean up front and scientifically rigorous if we were to get the independent verification we needed to ensure we could get it through peer review and into publication.

"We were obviously optimising our procedures along the way, and it has given use the confidence to move forward."