Question: On an average, how long would a stem cell generally take to develop into a full organ like a heart or a kidney? Also, can an organ developed from a stem cell from one individual be used by another individual ?

Matthew Tomlinson answered on 11 Nov 2013:

Wow, that’s a really tough question! There are a couple of answers so here goes.

To make an organ from scratch in the lab is really difficult, organs are very complicated and are made up of lots of different cell types that each do a job, so to begin with you need cells which can make all these types. Once you have these you need a scaffold to grow them on, this gives the cells something to hold on to and can also make them grow in the way you want them to. Once the cells are on the scaffold you can grow them in something called a bioreactor which gives them all the nutrients they need and other things like movement. After that you have something which is like an organ, although probably not exactly like the real thing, this whole process can take anything from a week for a small organ to a month or more for something larger. Last year a group in the US grew mini human kidneys and that took about 10 days.

Of course you could always start making an organ in the lab and then put it into the patient afterwards to grow properly. This method is really interesting because the body can direct the cells to grow into the organ you want. You can also put a scaffold into a patient on its own and let the patients own cells fill it up, this method has been used a lot in Leeds and there is a company that takes pig heart valves, washes all the cells out, and then puts them into people with damaged hearts. These pig scaffolds are then filled with the patients own cells and after about 6 months they have a fully working heart valve.

The reason these scaffolds work is because they have no cells on them so the patients immune system doesn’t think it’s ‘foreign’ and doesn’t try to get it out of the body. This is the big problem with any transplant because the immune system will reject something it doesn’t recognise as being from the patient. This is why people who are waiting for an organ transplant have to wait for a match and can’t just have the next organ available. This is because we all have a special protein on all of our cells, a bit like a barcode, which immune cells read, if they see it is your cell they will ignore it, if they see it as different they will try to kill it. Transplants work because proteins from two different people can be the same or close enough to trick the body into thinking it is from the same person. So if you were to make an organ from a different person’s stem cells you would still have the problems with rejection. The other option is to use induced pluripotent stem cells which are normal cells from skin or any other tissue which are turned back into stem cells, these can then be grown into other organs, just like an embryonic stem cell.

I hope that answers your question, sorry it’s such a long answer!