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How bones make blood - Melody Smith

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Bones might seem rock-solid, but they’re actually quite porous inside. Most of the large bones of your skeleton have a hollow core filled with soft bone marrow. Marrow's most essential elements are blood stem cells and for patients with advanced blood cancers like leukemia and lymphoma, the best chance for a cure is often a bone marrow transplant. How does this procedure work? Melody Smith explains.

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TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Melody Smith, Melody Smith
  • Director Igor Coric, Igor Coric
  • Narrator Bethany Cutmore-Scott, Bethany Cutmore-Scott
  • Animator Igor Coric
  • Storyboard Artist Igor Coric
  • Art Director Igor Coric
  • Sound Designer Cem Misirlioglu
  • Director of Production Gerta Xhelo
  • Editorial Producer Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Script Editor Eleanor Nelsen
  • Fact-checker Laura Shriver, Joseph Isaac
  • See more
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The production of red blood cells, white blood cells, and platelets in the bone marrow is called hematopoiesis (https://www.cell.com/trends/cell-biology/fulltext/S0962-8924(18)30102-8). Hematopoiesis in adults occurs within the bone marrow and requires the differentiation of stem cells into these three lineages of blood cells. These cells then circulate in the blood and each of them has a circumscribed role (https://www.hematology.org/Patients/Basics/). Red blood cells carry oxygen to the tissues throughout the body. White blood cells enable the body to fight infections and specific subsets of white blood cells fight bacterial, fungal or viral infections as foreign invaders. Platelets are critical for forming clots to stop bleeding.

Cancer is a heterogeneous group of diseases that are characterized by abnormal cell growth that may impact various organs in the body. Cancer may occur in the solid organs or it may impact the blood cells. Cancers of the blood cells include leukemia, lymphoma and multiple myeloma. Patients these blood cancer are initially treated with agents, which are referred to as chemotherapy. Chemotherapy can arrest abnormal cell of the blood cells growth. However, patients with blood cancers whose disease does not respond to chemotherapy or whose disease returns despite chemotherapy more intensive treatment may be needed. One potential option is to consider a an allogeneic hematopoietic cell transplant, also known as a bone marrow transplant (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2943393/), which may present the most likely option for a cure.

Oftentimes, the mention of the word “transplant” invokes the idea that the patient will need an operation. However, an allogeneic hematopoietic cell transplant is different from the transplant of a solid organ. An allogeneic hematopoietic cell transplant is similar to other transplants in that the recipient often needs a donor. If a patient does not have a donor within their family, then there are registries available to see if they have an unrelated donor. A donor is matched to the recipient by an immune classification called the human leukocyte antigen (HLA) complex. To learn more about the HLA complex, this link provides additional information: https://ghr.nlm.nih.gov/primer/genefamily/hla. Of note, the frequency and distribution HLA antigens varies by ethnic groups. This means that a patient in need of an allogeneic hematopoietic cell transplant is more likely to find a donor within a similar ethnicity to his or her own.

Sources of bone marrow for an allogeneic hematopoietic cell transplant include, peripheral blood and the bone marrow (https://bethematch.org/transplant-basics/how-transplants-work/). To learn more about alternative donor sources, such as cord blood (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5442719/) and haploidentical transplant (https://ascopubs.org/doi/10.1200/JGO.18.00130) please see the links provided.

The ultimate goal of an allogeneic hematopoietic cell transplant is to mediate graft versus tumor activity (https://ashpublications.org/hematology/article-lookup/doi/10.1182/asheducation-2017.1.693). Graft versus tumor activity refers to the anti-tumor activity that results when the donor’s T cells, which are a type of white blood cells, attack the cancer in the recipient. However, graft versus host disease may result if the donor’s T cells recognize differences in the HLA antigens between the donor and recipient (http://ar.iiarjournals.org/content/37/4/1547.long). This may cause significant morbidity and mortality when the donor T cell to attack the recipient’s organs, such as the GI tract, liver, or skin. Hence, when matching a patient with a donor great detail is given to the HLA compatibility.

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About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Melody Smith, Melody Smith
  • Director Igor Coric, Igor Coric
  • Narrator Bethany Cutmore-Scott, Bethany Cutmore-Scott
  • Animator Igor Coric
  • Storyboard Artist Igor Coric
  • Art Director Igor Coric
  • Sound Designer Cem Misirlioglu
  • Director of Production Gerta Xhelo
  • Editorial Producer Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Script Editor Eleanor Nelsen
  • Fact-checker Laura Shriver, Joseph Isaac
  • See more