Hematopoiesis Flashcards
How often do blood cells renew?
Depends on the cell type, between 0.5 day and multiple years. Every second 3-5 million new blood cells are produced.
Where are HSCs found and what is their niche?
In the spongy tissue of the bone marrow. The niche is not defined.
What were the main findings of the colony forming unit spleen assay and how do they indicate that there are stem cells in bone marrow?
The colony forming unit spleen (CFU-S) assay used bone marrow cells marked by chromosomal breaks and transplanted them into irradiated mice. CFU-S formed on the spleen of the mice and the colony number was proportional to the number of transplanted cells. Different cell types were found in the CFU-S, indicating multipotency. The chromosomal breaks were found in all cells, indicating proliferation potential. The renewal potential of CFU-S exhausted after a few weeks so they were later identified to be multipotent progenitor cells instead of stem cells.
How would you test for HSC?
Possible tests: colony-forming assays, (serial) transplantation assays of HSC into immunosuppressed mice, FACS to check for SC-specific surface markers.
How can you count the number of SCs in a cell population (two methods)?
The first method is the limiting dilution assay (LDA). A dilution series is made of the cell population. Each dilution is placed into wells, culture plates or mice, and the frequency of positive outcomes is counted per dilution. If one cell is used, the probability of a negative outcome is around 37% (according to Poisson statistics). This is used to estimate the number of cells in the population.
The second method is doing FACS with SC specific markers and count the cells.
What are challenges regarding clinical use of HSCs?
HSCs could be used clinically to rebuild a patient’s hematopoietic system, e.g. for leukemia patients. Challenges include that long-term maintenance and expansion of HSCs ex vivo is challenging, the SC purity in the BM is low which could lead to treatment failure, and it is difficult to find suitable donors.
