What’s the difference?
What makes embryonic stem cells different than adult stem cells than induced pluripotent stem (iPS) cells?
I can give you technical definitions and you can learn more here in my post “What are stem cells?”, but isn’t there an easier way to understand them?
I think we can use an analogy to help.
In this the analogy is between stem cells and different athletes in the Olympics.
Most athletes in the Olympics are specialists. They train most of their lives to try to win at one specific sport.
Michael Phelps is a swimmer and a champion, but could he pole vault? Could he compete in the long jump? Could he run a marathon? Could he do those things and win gold? I don’t think so. Hope Solo is an amazing goalie, a gold medalist. But could Hope run hurdles? Could she be a champion gymnast? Nope.
These athletes are amazingly good at one thing.
Like Phelps and Solo, adult stem cells are specialists. They are exceptional, but at just one type of thing. Each type of adult stem cell can only make one type of tissue. For example, muscle stem cells can only make muscle, but boy are they good at that. Blood stem cells are good at making blood.
Admittedly there are diverse kinds of blood cells, but then again some swimmers for example swim many types of races…it’s still swimming and not say, shot put.
Embryonic (ES) stem cells and iPS cells are the opposite. Instead of specialists, they are Renaissance cells (generalists) in the sense they are good at many things. ES cells are the decathletes of the stem cell world. They excel at making many other types of cells, far more than 10 in fact. Perhaps they could be called hectathletes (doing 100 sports).
But the point is that ES cells and iPS cells have this flexibility that the specialists, the adult stem cells, just don’t.
Further, by analogy one might say iPS cells, as Olympic athletes, were once specialists but converted to be decathletes or hectathletes. They re-trained and now re-focused on their new role as generalists.
Extending this analogy a step further leads to a logical question: at any one given sport that both a specialist and say a decathlete both do, isn’t the specialist always going to win head-to-head? Yep, I think so. A pure sprinter like Usain Bolt will always beat a decathlete in a sprint race. In the same sense, generally speaking adult stem cells are going to be better at their one specialty versus embryonic stem cells. For example, a fat stem cell is probably better at making fat than an ES cell. However, ES cells can do a good job making specific differentiated cells. It just might take them a bit longer and the differentiated cells they make could have slightly different properties than those coming from an adult stem cell.
Just as sports needs both generalists and specialists, we in the stem cell field need both adult and embryonic stem cells as well as iPS cells.
I hope this stem cell analogy to Olympic athletes is helpful.