Scientists have grown live human embryo replicas in the laboratory for the first time, with all cell types, biochemical activity, and general structure of real embryos.
The research, which aims to help understand the problems that cause miscarriages and birth defects, may raise fears about a slippery slope toward human genetic engineering and cloning.
But scientists conducting research at both Monash University in Australia and the University of Texas in the US say their creations, called blastoids, are not perfect replicas of real embryos and are not suitable for implantation in a uterus.
The research teams reported in the journal Nature on the creation of blastoids, cell assemblages that resemble blastocysts, the stage of embryonic development five to 10 days after fertilization of an egg.
For ethical reasons, there is an internationally accepted 14-day limit for the growth of human embryos for research and, until now, scientists working on live models such as blastoids have observed the same limit.
The International Society for Stem Cell Research, the professional body in the field, aims to address ethical concerns by soon issuing new guidelines for the creation of embryos from stem cells.
“The blastoids will allow scientists to study the early steps of human development and some of the causes of infertility, congenital diseases, and the impact of toxins and viruses on early embryos, without the use of human blastocysts. [from IVF] and most importantly, on an unprecedented scale, accelerating our understanding and development of new therapies, ”said José Polo, Monash project leader.
Both teams grew their blastoids from stem cells, derived from reprogramming adult cells or extracted from embryos. The cells were treated with biochemical cocktails and cultured in laboratory dishes containing a culture medium designed to develop like real embryos.
After culturing for a week or so, the cells had become blastoids similar in size and shape to natural blastocysts. They contained more than 100 cells that began to differentiate into various types of cells that would later produce different tissues in an older fetus.
Some of the blastoids exhibited a behavior that mimicked implantation in the uterus, as they attached to the culture plate and developed new cells that could become placenta.
The scientists insisted that although blastoids would be very valuable in studying what happens in early pregnancy, they should not be considered synthetic embryos. “There are many differences between blastoids and blastocysts,” said Jun Wu, team leader from Texas. “The blastoids would not be viable embryos.”
Last June, Naomi Moris and her colleagues at the University of Cambridge published groundbreaking research on a later phase of embryonic development. His laboratory overlooked the early stages of development represented by blastoids and produced simplified models of older embryos (18-21 days).
“This is a very exciting time for human embryology,” said Moris, who moved to the Crick Institute in London. “New tools and stem cell technology are producing an influx of embryonic models, giving us the opportunity to understand how we develop from a single cell to a full human being.”
In May, the ISSCR’s international watchdog is due to issue new ethical guidelines for culturing stem cell-based models of embryos, “offshoots,” as some call them. “Research using these models has the potential to understand a developmental period often referred to as the ‘black box,'” said Professor Amander Clark of the University of California, Los Angeles, who is part of the society’s working group that update research guidelines.
“The models have the potential to improve infertility treatments and interventions for congenital heart and brain defects and other genetic diseases,” he added. “As these models continue to advance, research review committees will need a set of criteria to review the admissibility of research proposals.”
Meanwhile, research on artificially reproducing mice, unrestricted on ethical grounds, has advanced much further. Scientists at the Weizmann Institute in Israel reported in the same issue of Nature that mouse embryos had grown healthily for 11 days, just over half their normal gestation period, in an artificial uterus or womb.