The Production of New Blood Cells

Millions of our blood cells die and are replaced every day. The production system for these critical cells Is an orchestrated process of growth and development of specialized cells from Immature precursors, driven by protein factors. This only happens once we are adults. The general process is named for the differentiation—the change from an unspecialized ceii to a speciaiized cell able to do a job because of the presence of particular proteins. 

A single type of precursor cell, the hematopoietic stem ceii, gives rise to red blood cells, white biood ceils to fight Infections and populate our Immune system, and platelets to help heal wounds and plug up leaks In blood vessels. 

Except for lymphocytes, each specialized blood cell Is a workhorse at the end of its road each remains in the circulatory system or In a tissue and then dies, perhaps as a result of doing its job. Red ceiis (erythrocytes) have lost their nucleus, and platelets are fragments of precursor cells. Because they have no nuclei, human red cells and platelets cannot divide. 

Proetyihroblast Basophilic Polychromaiic Normoblast Reliculocyle erythrobla t f hrobla t 

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SA is known to accumulate in the body. It displaces calcium in bone matter and impacts the production of new blood cells in bone marrow. S A enters the bloodstream... 

Strontium-90, a radioactive strontium isotope with a half-hfe of 29 years, is a dangerous fallout source of radiation from atmospheric nuclear bombs. If a person is exposed to it, it will rapidly accumulate in bone tissue and interfere with the production of new red blood cells... 

Figure 6.1 An RNA viral gene therapy vector, engineered to carry the genetic information for a protein product, is incubated with blood or bone marrow cells removed from a patient. The foreign DNA sequence integrates into the cell s genetic material and when the cells are returned to the patient, they direct the production of the protein product. RNA gene therapy vectors are engineered to be unable to direct the production of new virus particles.

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic stimulant (i.e., encourages formation of new blood cells and is given to patients who have undergone chemotherapy, bone marrow transplants, etc.). It can be produced by expression from genetically modified . coli, as described in U.S. 4,810,643 Example 7. Estimate the cost of production of hpG-CSE using the method of this example. 

Adaptation by enzyme replacement is more important in nondividing cells than in a continuously growing population. In the latter case, a less appropriate enzyme complement can be diluted out by daughter cells containing enzymes more suitable for the new nutritional state. A limited life for the cells would also facilitate such adaptation. However, adaptation via the production of new cells is only relevant to those mammalian cell types where the cells are not physically confined to a discrete area or to those cells which have a short life span. Examples are sperm, erythrocytes, other blood cells, and gut mucosal cells. Yet these cells are typically highly specialized, of relatively constant composition, and rarely show adaptation. 

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