Re: How are Embryonic stem cells harvested?

Dear Tracey,
Embryonic stem cells are isolated from preimplantation blastocysts, about 
3.5 days after fertilisation has taken place. The cells of the inner cell 
mass/epiblast region are removed from the rest of the blastocyst and 
cultured on a layer of primary embryonic fibroblasts (isolated from day 
13.5 old embryos). The layer of fibroblasts (called a feeder layer) secrete 
factors that stimulate the undifferentiated growth of the ES cells. The 
cells are then grown in large quantities and frozen for future studies. The 
trick to isolating ES cells is to have the best growth conditions possible 
otherwise the ES cells will differentiate (form into other cells types) and 
will be useless for further studies. Human ES (hES) cells depend entirely 
on the quality of the feeder layer and growth medium to maintain 
undifferentiated growth. In contrast, mouse ES cells can be grown in the 
absence of a feeder layer in leukaemia inhibitory factor (LIF), a cytokine 
that prevents ES cell differentiation. The Holy Grail of hES cell culture 
is to find a substance that can be added to the cells to prevent them 
differentiating (LIF doesn't work on hES cells). At present both mouse and 
human ES cells are extremely useful to scientific and medical research 
since they can divide indefinitely and be induced to differentiate into 
many adult cell types. However, prolonged culture of these cells in the 
laboratory can lead to genetic abnormalities.

The legislation of ES cells is changing all the time and I do not know this 
area in detail. However, the UK and Australian Governments allow isolation 
of ES cells from human blastocysts and subsequent growth of the cells in 
the laboratory. The UK also allows "therapeutic cloning", where an ES 
cell line can be made (using the technology used to make Dolly the sheep) 
containing a specific genetic makeup. In the USA, only ES cells isolated 
before August 9th 2001 can be used for federal funded research. However, I 
believe that private funding can still be used to isolate blastocysts from 
human embryos in the USA although therapeutic cloning is, as far as I know, 
illegal. 

The NIH website (www.nih.gov) has a lot of information on the use of human 
ES cells.

I hope this is of some use to you.
Best regards,
Chris Ward