Friday, November 19, 2010

Podcast:Converting skin cells straight into early blood cells

"We are really interested in what mature cells we could make for the purposes of cell replacement therapies in regenerative medicine. We realized that we could make these mature blood cells of specific types, so we could make neutrophils, which operate to optimise bacteria; macrophage which engulf foreign particles in the body. We also made red blood cells and another cell type called the megakaryocyte which makes Platelets which is essential for coagulation, blood in wound healing"
Geoff Marsh: Stem cells have had scientists excited because they have the ability to become any cell in the body. More recently introduced for IPS cells, adult cells that can be reprogrammed back to a primitive stem cell like state. This is achieved by bathing these cells in chemicals called transcription factors which instruct the cells to reprogramme into different cell types. Now a Canadian team has managed to convert skin cells straight into early blood cells completely bypassing the reprogramming step. How exactly, I spoke to Mickie Bhatia.
Mickie Bhatia: We certainly capitalized on a lot of work done previously on with human skin fibroblasts. I think as we said the induced pluripotent stem cells demonstration showed that those cells had potentials beyond just remaining skin and we are really interested in this is what mature cells we could make for the purposes of cell replacement therapies in regenerative medicine and our approach was to specifically a blood as an area of example, many there is a lot known about the blood system and it's already used clinically in bone marrow transplants and transfusion medicine so we thought if we were starting on the human that was a good choice, a lineage to look at.

Geoff Marsh: So what did you do these cells, you added some sort of concoction?

Mickie Bhatia: We did. Yeah. It took certainly a lot of trial and error. We were very interested in how the reprogramming process actually takes place when you reprogram them to IPS state. And one of the things that we realized that there might be other potentials that one starts to see before you generate an IPS that other cells might emerge, but the conditions that those skin themselves were grown in were specific to retaining a pluripotent cells. So we wanted to know was the factors that had been worked out already with IPS, transcription factor specifically. Was there a specific transcription factor combined with growth factors proteins that can be added to the Petri dish that might allow us to select and differentiate or convert as we have now coined it to another lineage and we basically did trial and error working on a combination of timing, when we added the haematopoietic growth factors and which specific transcription factor was to be added. And we ended up identifying one that worked which was an OCT protein that had to be put in to the skin cells in combination with a very specific timing of when we add haematopoietic growth factors that allowed us to demonstrate that the fibroblasts had the ability to produce blood progenitors.

Geoff Marsh: This mixed to this OCT protein you added to the cells?

Mickie Bhatia: And when we put in OCT and you combine it with the haematopoietic growth factors, it actually would turn ON and OFF unique genes that were specific to blood generation. In the absence of those growth factors, it actually did something very different. So, it seems like you could externally regulate what OCT was doing in the cell by providing or bathing the cell with different proteins. It wasn't just the factor that you used the transcription factor that you put in, it had to be put in a cell that was treated in a different way, because that cell will cease signals and that it allows OCT to do different things in it. And I think it's a combination, well we show that it was that combination that actually allowed the conversion to take place. That hadn't been done before. OCT had been used to make induced pluripotent cells but those cells were always cultured in vitro under conditions that were trying to find the pluripotent cell. And OCT never worked on its own, it would, to induce pluripotent stem cell you had to have OCT with other transcription factors, so it sort of needed assistance to help it, reprogram cells to a pluripotent state.

Geoff Marsh: OCT so much drives the transformation whereas the other transcription factors in the specific proteins that you mix with it direct which way it goes.

Mickie Bhatia: Exactly, exactly.

Geoff Marsh: So, you know you added this mixture and you started off with skin cells, and tell us about the blood cells that you created. How do they shape up to healthy adult blood cells?

Mickie Bhatia: Yeah, so we realized that we could make these mature blood cells of specific types, so we could make neutrophils, which operate to optimise bacteria; macrophage which engulf foreign particles in the body. We also made red blood cells and another cell type called the megakaryocyte which makes Platelets which is essential for coagulation, blood in wound healing. So all of those cell types could be generated but we could also generate a progenitor of those cells, so it is the cell that isn't fully differentiated yet. It retains some ability to duplicate and proliferate before it successfully turns into a cell that functions in the body and we felt that it was a benefit because it allowed us to grow the cells in larger quantities prior to internal differentiation. It turned out that the red blood cells we produced from these adult skin samples was actually adult blood and so they actually expressed adult haemoglobin which is quite different than the red blood cells that one can generate from either human ES or human IPS. They normally, because they keep that in an embryonic state when they differentiate they produce foetal haemoglobin which isn't' as useful if you're transplanting or envisioning transplantation into adults.

Geoff Marsh: Why does that make these cells more useful then? What are their clinical applications?

Mickie Bhatia: Absolutely, I think the foetal and embryonic, they can certainly do the job those haemoglobins but they actually do it too effectively. They actually have almost a 70 times higher affinity for oxygen and that's not the kind of cell you want to transplant into a person because the oxygen requirement would be too high.

Geoff Marsh: So, theoretically in the future, a patient could come in with a need for blood and could therefore, you know, use some of his or her own skin cells to grow their own blood.

Mickie Bhatia: Yeah, absolutely and the fact that we can use their skin cells means there is no risk of rejection when transplanting those blood cells back in. And in our hands at least the process is also more efficient than generating blood from either ES or IPS, in addition to the third benefit which is generating adult cells. So those are the kinds of things in the future we are going to be optimizing and working on., you know, even to the point of seeing if we can freeze and thaw the blood cells we generate so that we have a storage of these cells should patients require them and then I think there are the already blood banks to develop some of the cryopreservation technology required.

Geoff Marsh: I mean presumably you can't grow your own blood in, you know, 10 minutes. So you can't come in with horrible trauma and grow your own blood there. So, you know, could you just give us a sense of a situation when this will be really useful?

Mickie Bhatia: Yeah, certainly I think in the acute case that you mentioned we envision taking skin cells from different healthy donors that are of different blood types, for example B positive or negative, generate those cells and we are hoping we can actually cryopreserve them. So in the cases you indicated earlier where there is an emergency, a trauma, or where there is a direct need for transfusion, one could use storage of skin-derived blood cells as a possibility. The other application that we are thinking a lot about is using this for patients, for example, with leukaemia where there is a genetic alteration in their blood that makes their blood cancerous. By taking their skin cells which do not have that genetic mutation and generating these blood cells we provide an alternative source that could replace some of those leukemic cells and we think it would add to the current therapy that they go under. So it's certainly envisioned a requirement for chemotherapy. But one of the problems with chemotherapy is it kills off highly growing proliferative cells which includes the blood. So you always need an alternative source and because the therapies usually strategize as to when it is going to start they would be sufficient times to prepare skin sample that to be diverted that can be used in those types patients.

Geoff Marsh: That was Mick Bhatia of McMaster University in Canada.
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