How to separate cancer cells from normal stem cells?

by Alexey Bersenev on August 6, 2009 · 7 comments

in cancer stem cell, leukemia, under discussion

 
I was thinking about it for a long time. Especially after that discussion about our satisfaction with hematopoietic stem cell transplantation that we had. The question I’ve been asked was whether it’s possible at all? I was almost sure it is, as referred to in Irving Weissman’s talk (slide on 11 – 13 min). He basically said that we can “remove contaminating cancer cells from stem cells grafts”, based on sorting different populations by surface markers.

But recently I realize that he didn’t say anything about cancer stem cells (CSC). If leukemic stem cell (LSC) share surface markers with normal hematopoietic stem cell (HSC), how can we separate them? By that time (2007) Weissman hadn’t noticed. Modern blood separators that are used in bone marrow transplant clinics for autologous grafts cannot give us CSC-free apheresis product.

I started to search more information about it. What I found was that there are a few experimental approaches, which could give us a hope for possibile separation of CSC from HSC in mobilized peripheral blood of leukemic patients. All of these approaches are once again based on elimination of CSC by surface markers. Even though they share expression with normal HSC the level of signal is so much higher that all activity of eliminating antibody will be directed to CSC without significant depletion of HSC.

The identification of cell-surface molecules that can distinguish between leukemic and normal stem cells is essential for flow cytometry-based assessment of minimal residual disease (MRD) and for the development of prospective separation strategies for use in cellular therapies.

Here are some markers that are proposed to discriminate normal HSC from leukemic stem cells:

As you can see some markers were described a while ago. I was trying to track their following development in terms of clinical trials and didn’t find any information. I assume, for now, all of them are stuck in “xenogeneic assays stage”. CD47 is the latest “new hope” for clinical trials, and it could have some advantages:

We demonstrate not only that CD47 is more highly expressed on AML LSC compared to normal HSC and MPP but also that this differential expression can be used to separate normal HSC/MPP from leukemia cells. This demonstration of the prospective separation of normal HSC from leukemia cells in the same patient sample offers the possibility of leukemia-depleted autologous HSC transplantation therapies.

If you know any other approaches which got very close to clinical trials and that I didn’t mention here, please discuss in comments. For now, I can’t wait when we will get a “magic blood separator”: up right – T-cells, up left – cancer stem cells, low right – HSC, low left – myeloid progenitors. Jut hit a “start” button!

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citations: Majeti R, et al. Cell 2009;138:286

{ 7 comments… read them below or add one }

Mark Gagnon October 8, 2009 at 2:12 pm

Alex, I would like to talk to you further about this.

I have MDS with two cytogenetic mutations (translocations of chromosome 7 and 15). One third of my cells are normal. I assume when they do cytogenetic analysis they are only looking at the stem cells. I have been wondering two things:

Is it possible to separate the normal healthy stem cells from the mutated ones?

If it does become possible to separate them, then will an autologous stem cell transplants work? (My understanding is that the oblation process is incomplete and in a allogeneic transplants the new immune system kills off the remaining blood line cells. But then you have to deal with immunosuppressing drugs and graft vrs host.)

Reply

Alex October 10, 2009 at 3:12 pm

Mark,
I don’t think this separation is possible with high purity of healthy stem cells at this time point.
But there is autologous transplant for MDS. Unfortunately probability of relapse higher then with allogeneic transplant.
All official information you can find here –
http://www.marrow.org/PATIENT/Undrstnd_Disease_Treat/Lrn_about_Disease/MDS/MDS_Transplant_Outcomes/index.html

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Mark Gagnon October 10, 2009 at 4:28 pm

Thank you Alex, for passing along the website. I have read much of the literature on outcomes and am now trying to develop a deeper understanding of stem cells and the ablation process. Can you point me to research literature that reports on the process and results of stem cell separation techniques?

With the advances in “growing” organs, and a statement I read that “a single stem cell can repopulate the bone marrow”. Is this statement indeed factual? Again, can you point me to literature that deals with this?

May I ask again, isn’t it the incomplete ablation process and likelihood of relapse that is the ultimate hurdle?

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Alex October 13, 2009 at 12:12 am

Mark,
In general, many techniques described in the books. For example – http://books.google.com/books?id=t36hMIgKOeEC
http://books.google.com/books?id=8kdFhqeZO10C
You can read it for free up to 50% of content through Google Books.
In simple terms, most HSC transplantations in the clinic divide for unmanipulated (whole BM or mononuclear fraction – MNC) and manipulated grafts. Most of manipulations – T-cell depletion, stem/progenitor cell enrichment (CD34+ total by CliniMACS or Isolex devices) or expansion.
There are tons of research literature on this. I don’t know what is your interest in particular.
Statement “a single cell can repopulate the BM and rescue organism from lethal irradiation” is factual and valid but for mice. There are a few studies proved that, for example – http://www.sciencemag.org/cgi/content/abstract/273/5272/242
For human we don’t know for sure about the single cell, but in humanized mice model we can rescue entire BM and blood by as few as 10 cells – http://hematopoiesis.info/2008/01/21/hierarchy-of-human-hematopoesis-scheme-is-updated/

To answer your last question I’d say I don’t think so. Now we can play with intensity of ablation/supression and many studies going on aimed to unveil the reasons of relapses and possible ways of their prophylactic.

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Parwathy Chandran August 27, 2010 at 3:19 am

Alex, I’m doing my PhD in the area of nanomedicines targeted to cancer stem cell. We are initially probing whether the AML stem cells could be targeted sparing the HSCs, so that we can deliver the drugs specifically to the cancer stem cells. Do you think that it could be a viable way to eradiacte these cancer stem cell fraction, in vivo?

Reply

Alex August 27, 2010 at 3:32 am

Parwathy,
Yes, I think it’s a reasonable way. The only problem how to identify AML LSC? I don’t advice you to use surface phenotype. To deliver something into the cell precisely you need to know the identity or characteristics of this cell population. It could be expression on molecules on the surface, could be expression of genes or production intracellular proteins, metabolism and function or microenvironment. All of these parameters of identity could be targeted in different way.
The surface phenotype works nicely for normal stem cells, but apparently doesn’t work for cancer stem cells, at least for some types.

On the other hand, there is a mounting evidence that you need to kill all cancer cells withing the tumor, because cancer non-stem cells and evolve and become cancer stem cells (reprogramming) on later stages of disease and vise versa.
So, such markers as CD47 and CD123 which overexpressed in leukemias, but not only in LSC subset, can be good therapeutic targets.

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Parwathy Chandran August 27, 2010 at 9:03 am

Alex,
Thanks a lot for the information.

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