Scientists have managed to create models of early human embryos in the laboratory using either adult skin cells or pluripotent stem cells. Both techniques are revolutionary, opening the way to a wide range of research.
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The 3D models, which are similar to human blastocysts, have been named iBlastoids. Scientists hope that iBlastoids can be used to model the biology of early human embryos and also allow for better study of the causes of early miscarriage, the causes of infertility, and the effects of drugs and toxic substances on fetal development.
In the first study, researchers from Australia, the USA, China and Singapore, led by Professor Jose Polo of the Biomedical Discovery Institute of the Australian University of Monas, who published the relevant publication in the journal "Nature", reprogrammed human skin cells (fibroblasts) to transform into a three-dimensional spherical cellular structure, which morphologically and molecularly is similar (but not completely identical) to the human blastocyst, that is, the initial - just a few days - stage of embryo development.
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This laboratory embryo model (iBlastoid) can now be used – instead of a normal embryo – to study embryonic biology. Until now, the only way to study the first days of an embryo has been from donated blastocysts obtained from the in vitro fertilization process, which limits their availability. More recently, other scientists have grown blastocyst-like structures in mice, but this is the first time something similar has been done using human cells. “iBlastoids will allow scientists to study the very early stages of human development and some of the causes of infertility, congenital diseases and the impact of toxins and viruses on early embryos, without the need for the use of human blastocysts, thus accelerating our understanding and the development of new treatments,” said Jose Polo.
Infertility and early miscarriage occur within the first two weeks after conception, when women are not even aware they are pregnant. These “silent” miscarriages probably account for a significant proportion of the total number of miscarriages worldwide. iBlastoids will enable scientists to shed more light on these hidden miscarriages.
In the second study, also published in Nature, researchers led by Professor Jun Wu of the University of Texas Southwestern Medical Center followed a different strategy, starting with human pluripotent stem cells to grow three-dimensional blastocyst-like blastoids in the lab. The lab-grown blastocysts resemble human blastocysts in morphology, size, cell number and composition. They stressed, however, that these blastocysts are not exactly equivalent to blastocysts and cannot develop into a viable human embryo.
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However, this new research, which takes about a week to grow the blastocyst models in the lab, raises bioethical issues. Given that there is no legal precedent regarding research on blastocyst models like iBlastoids, and considering that international scientific guidelines are that human blastocysts should not be grown in the lab (in vitro) beyond day 14 of embryonic development, Polo and his colleagues did not grow the iBlastoids beyond day 11.
The new guidelines of the International Society for Stem Cell Research are expected soon, and it is not known whether they will include anything about new laboratory blastocysts such as iBlastoids.
The researchers managed to create the iBlastoids using a technique called “nuclear reprogramming.” This allowed them to change the cellular identity of human skin cells that – when placed in a three-dimensional gel scaffold, known as an extracellular matrix – organized into the blastocyst-like structures that gave them their name.
