Blast Cells

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Blast Cells

Hematopoiesis (blood formation): The myeloid cell line begins with a myeloblast. © McGill Molson Medical Informatics Project. Used With Permission.

What Are They?

In biology and in medicine, the suffix "-blast" refers to immature cells. You can have blasts that give rise to all kinds of different specialized cells. So for example, neuroblasts gives rise to nerve cells; adipoblasts give rise to fat cells, or adipocytes, etc.

Just as nerve and fat cells develop from immature precursor cells, blood cells also come from immature blood-forming cells, or blasts, in the bone marrow. Blood cells are continually formed to replace those that have become old or worn out. In healthy bone marrow, blood-forming cells known as hematopoietic stem cells develop into red blood cells, white blood cells and platelets through a process called hematopoiesis.

Myeloblasts, or Blast Cells

Myeloblasts are a particular kind of immature cell or blast found in the bone marrow—and not normally found in the peripheral blood. Myeloblasts are the earliest “morphologically distinct” cells of the cell family known as the myeloid cell line; morphologically distinct means you can tell them apart by their microscopic appearance. They myeloid cell line includes red cells, white cells and platelets, but myeloblasts give rise only to the white blood cells that have granules inside, as seen in microscopy. This family of white blood cells includes neutrophils, eosinophils, basophils and monocytes and macrophages.

Myeloblasts Are Often Referred to Simply as “Blasts”

Myeloblasts, or blasts, are normally found inside certain bones, in the bone marrow. The presence of these myeloblasts circulating out in the bloodstream can be an important indicator of certain diseases such as acute myelogenous leukemia and myelodysplastic syndromes.

Acute myeloid leukemia also goes by several other names, which according to the American Cancer Society include: acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, acute non-lymphocytic leukemia, or sometimes just AML. It is most common in older people. Most cases of AML develop from cells that would turn into white blood cells other than lymphocytes, however some cases of AML develop in other types of blood-forming cells.

Myelodysplastic syndrome is a group of disorders that affect the production of new blood cells in the bone marrow. In these diseases, the bone marrow produces abnormal blast cells that fail to mature properly and are unable to function.

Where Do Myeloblasts Come From?

Very early on in hematopoiesis, or blood cell formation, the stem cell chooses its path of development or "cell line." There is a common myeloid progenitor and a lymphoid progenitor. One cell line, the lymphoid cell line, ultimately results in B-lymphocytes and T-lymphocytes. The other cell line, the myeloid, leads to the development of platelets, red blood cells, neutrophils and other types of white blood cells. In the myeloid cell line, the term "blast cells" refers to myeloblasts or myeloid blasts. These are the very earliest and most immature cells of the myeloid cell line.

Although the cells of the myeloid cell line make up about 85% of the cells in bone marrow, less than 5% of them in the bone marrow should be blast cells. Additionally, blast cells are not typically found in the circulating blood of healthy individuals.

In the case of acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS), there is an overproduction of abnormal myeloblasts. These cells are unable to develop further into mature white blood cells.

These abnormal blasts begin to take over the bone marrow and prevent production of adequate numbers of other types of blood cells, such as platelets, red blood cells, and healthy white blood cells. In fact, production of leukemic blasts may get so out of hand that the immature cells spill out from the bone marrow into the circulation. The presence of blast cells on a complete blood count (CBC) is therefore very suspicious for leukemia.

Sources:

Larson RA, Le Beau MM. Prognosis and Therapy When Acute Promyelocytic Leukemia and Other “Good Risk” Acute Myeloid Leukemias Occur as a Therapy-Related Myeloid Neoplasm. Mediterranean Journal of Hematology and Infectious Diseases. 2011;3(1):e2011032.

Zahid MF, Parnes A, Savani BN, Litzow MR, Hashmi SK. Therapy-related myeloid neoplasms - what have we learned so far? World Journal of Stem Cells. 2016;8(8):231-242.

"Comprehensive Review of Hematopoiesis and Immunology: Implications for Hematopoietic Stem Cell Transplant Recipients" in Ezzone, S. (2004) Hematopoietic Stem Cell Transplantation: A Manual for Nursing Practice Oncology Nursing Society: Pittsburgh, PA (pp.1- 12)

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