Stem Cell Heirarchy Part Two

Question 1

How would we define a cancer stem cell?

Answer 1

• Does it perpetuate the tumour (through serial transplantation in animal models)?
• Does it give rise to the range of cells found in the tumour, including clonogenic cells and non-proliferating progeny? (transplanted tumour stem cells should recapitulate the differentiation and maturation pattern of the original tumour).
• Does it have a defined phenotype?
• Is it rare?
• Is it quiescent?

Question 2

What evidence can we gather/has been gathered for proof of the self renewing cancer (stem) cell?

Answer 2

• CD133+ marker and asymmetric division evidence - even within a cancer we will find CD133+ and CD133- tumour cells. There will probably be a minority of CD133- cells within the tumour. Also there might be some CD133+ cells. We can look at cell division and see if one of the daughter cells is CD33+ and the other is CD33- (asymmetric division).
• Evidence that when CD133+ tumour cell subpopulation selectively transplanted, phenotypically the transplanted tumours were similar to the original tumours, even to the level of expression of CD133.
• As is the case for that the CD34+CD38- subset contain the stem cells in normal haemopoiesis, a CD34+CD38- subset is also an engrafting subset in AML cells. When sorted out this subset were shown to graft NON-SCID mice in repopulation assays. CD34+CD38- cells from leukaemia patients were found capable of recapitulating the leukaemia in NOD/SCID mice.

Question 3

What % of cells are thought to have stemness properties in AML?

Answer 3

• In normal haemopoietic cells 1 in 300,00 BM MNCs are thought to have stemness properties.
• In AMP, from <1 in 1, 000,000 to 1 in 20,000 PM MNCs - very variable % measurements. May be rare or extremely rare.

Question 4

Is a cancer stem cell phenotype similar to a normal stem cell phenotype?

Answer 4

• To some extent yes. A cancer stem cell phenotype is often similar to a normal stem cell phenotype.
• CD133+
• CD34+CD38 (AML)
• Side population (pop of cells to side of main pop seen on flow cytometry when Hoechst is used) - because stem cells tend to be rich in drug efflux pumps Hoechst dye will be effluxed from the stem cells so we see a side population.

Question 5

If an AML cell population is capable of recapitulating AML on transplant does that mean it is definitely an AML cancer stem cell population?

Answer 5

• No, in experimental murine models AML can be induced by progenitor cells as well as stem cells.
• Cancer can arise from a progenitor cell that has re-acquired the self-renewing properties of a stem cell.
• This implies that the cancer stem cell does not have to be derived directly from the normal stem cell.

Question 6

Does a cancer stem cell have to be derived directly from a normal stem cell?

Answer 6

• Cancer can arise from a progenitor cell that has re-acquired the self-renewing properties of a stem cell.
• This implies that the cancer stem cell does not have to be derived directly from the normal stem cell.
• This is a major difference between a cancer stem cell and a normal stem cell.

Question 7

What transcription factors are thought to be aberrant in cancers?

Answer 7

1) . MLL - found in about 10% of acute leukaemias. Has 71 known fusion partners - most commonly the 4:11 translocation found in ALL and 3 translocations found in AML.
2) . TEL/ETV6 - 48 known fusion partners, inversion, and insertions of TEL including the inversion of 12p in AML and MDS. Other translocations found in ALL and CMML.
3) . RUNX AML1 - involved in a number of translocations and mutations and is also found in the very common 8:21 translocation in AML. Is often found mutated in AML and in other myeloid malignancies.

Question 8

Summarise the characteristics of the cancer stem cell.

Answer 8

• A cancer stem cell can perpetuate a tumour through serial transplantation.
• They should give rise to the range of cells found in the tumour, including clonogenic cells and cells that are terminally (albeit incompletely) differentiated, (i.e. transplanted tumour stem cells should recapitulate maturation pattern of original tumour).
• Not always a defined phenotype in the cancer stem cells.
• Cancer stem cells are not always rare.
• They are not always dormant.
• Don’t necessarily derive directly from stem cells.

Question 9

Discussion/revision question. Haematopoietic stem cells: Do they fit the job description? What is the experimental evidence for this?

Answer 9

1) . Versatility:
- Clonality studies
- Phenotyping followed by genetic analysis

2) . Productivity:
- Unexpected finding that stem cells are rare

3) . Retain stemness:
- Asymmetric division