Stem cells, blood and the immune system

This information about the human body and the immune system will assist you in understanding the stem cell transplant process.

What are stem cells?

The bone marrow is similar to a factory that makes blood cells. Bone marrow is a spongy substance found in the center of the bones.  In the bone marrow, there are seed cells or parent cells, called stem cells.  Stem cells can become any one of the of blood cell types: red blood cells, white blood cells, or platelets.  Besides the bone marrow, stem cells are found in umbilical cord blood and in the peripheral blood.  Many of the bones    of your body contain bone marrow.  The easiest place to obtain bone marrow is in the hip bones.  In addition, the hip bones are also the location where bone marrow samples are obtained from the patient when needed for a bone marrow exam. 

What are Blood Cells?

Red Blood Cells.  Red blood cells (RBCs) carry oxygen from the lungs to all of the tissues in the body.  There are two measures often used to quantify the amount of red blood cells:

  • Hematocrit (Hct). The percentage or portion of the blood made up by red blood cells. Normal is about 33%.
  • Hemoglobin (Hgb). The amount of oxygen-carrying protein in the blood, common range is 12-16grams/dL.

Normal ranges of hematocrit and hemoglobin are based on age and sex.  However, children who have received chemotherapy and/or radiation often do not have these normal ranges.  When the hemoglobin is low your child may experience symptoms of anemia such as fatigue, pale skin, increased heart rate, dizziness, shortness of breath. Your child may receive a blood transfusion when he/she experiences these symptoms.  Red blood cells may take up to 12-90 days to recover post transplant; but due to the differences in red blood cell survival and the blood volume the actual blood type switching may take several months. Transfusions are discussed in more detail in the “After Transplant” section of this handbook. 

White Blood Cells.  Many types of white blood cells (WBCs) help the body fight infection and disease. When the WBC count is low, an infection can occur very easily because the body has lost one part of the immune system which fights germs and viruses. There are three major types of white blood cells: neutrophils, monocytes, and lymphocytes. White blood cells can take anywhere from 12-42 days to recover after transplant, but recovery times are different for each patient.

  • Neutrophils. These cells are the body’s primary defense against harmful bacteria. They are the major cells that fight all bacterial infections. When neutrophils are low and the person has a fever of 100.5o F or more, intravenous (IV) antibiotics are given to help fight the bacteria.
  • Monocytes – these cells help in the fight against bacteria and mainly fight fungal, protozoan or parasitic infections.
  • Lymphocytes. These cells help protect the body by making antibodies and regulating the immune system response. These cells fight all types of infections including bacterial, viral and fungal. There are two types of lymphocytes, T-cells and B-cells. T-cells recognize any foreign matter in the body and directs the immune system to attack these foreign substances. T-cells also activate the B-cells to produce antibodies that recognize a previous infection and attack the foreign substances more efficiently. B-cells are the primary source for antibody production.

Platelets.  Platelets have irregular-shapes and sticky surfaces that let them, along with other substances, form clots to stop bleeding. Platelets help prevent bruising and bleeding. When your child has a low platelet count, or has evidence of bleeding, a platelet transfusion will be given. Petechiae are small red or purple spots on the body, caused by minor bleeds from broken capillary blood vessels. These may also appear on the skin, mouth or on the eyes when the platelet count is low. Platelets can take up to 28-90 days to recover post transplant: again, recovery times are different for every patient.

The Immune System

The immune system is a complex system that creates the body’s defense against infection. The immune system is made up of white blood cells, the spleen, the thymus gland, and lymph nodes. The immune system is able to recognize self and identify substances that belong in the body and substances that are foreign to the body. The immune system is genetically programmed to attack any foreign or “non-self” substance.