Hematopoietic Stem Cells: What Are They and What is Their Function?

Most of us understand the importance of blood cells. Red blood cells carry oxygen throughout the body while white blood cells fight infection and help us develop immunity to diseases. But, what about the stem cells that turn into our blood cells?

Scientists, researchers, and doctors have been studying hematopoietic stem cells (HSCs) – the stem cells that form blood and immune cells – for over 60 years, starting after the bombings of Hiroshima and Nagasaki in 1945. They’re now routinely used to treat patients with cancer after chemotherapy.

What Is A Hematopoietic Stem Cell?

The hematopoietic system – the system responsible for the production of the bodies’ cellular components – relies on the presence of HSCs.

In fact, HSCs are the only source for the continued production of red blood cells, platelets, white blood cells, and all other cells in the system. When you consider the fact that the average human requires around 100 billion new hematopoietic cells each day, you realise how vital the role of HSCs is in each of our bodies.

Identifiable Traits of Hematopoietic Stem Cells

Because HSCs behave like normal white blood cells, scientists have spent a considerable amount of time identifying key properties and characteristics of the stem cells.

Studies on mice laid the groundwork for our current understanding, and we now know that a HSC has four important properties: it can renew itself, it can differentiate to a variety of other specialised cells, it can mobilise out of bone marrow into circulating blood and it can undergo programmed cell death, called apoptosis.

We also know that there are several different sources of HSCs, including bone marrow, peripheral blood, umbilical cord blood, fetal hematopoietic system and embryonic stem cells and germ cells.

Bone marrow has been used as a source of HSCs for over 40 years  But, peripheral blood is now the preferred source for medical treatments and, as umbilical cord blood banks are receiving more and more support around the world, umbilical cord blood is being considered a more viable option for patients as well. The final two sources – the fetal hematopoietic system and embryonic stem cells – are used for clinical purposes only.

Clinical Uses and Current Applications

Today, tens of thousands of transplants are performed annually around the world.

Medically, HSCs are used to treat patients with acute myeloid leukemia, chronic myeloid leukemia, acute lymphatic leukemia, aplastic anemia, and other primary immune deficiencies and metabolic diseases. In treating cancer patients, HSCs are transplanted after chemo- or irridation therapy to regenerate the hematopoietic system. In most cases, this is achieved in just 2-4 weeks.

The Future

Current clinical trials are looking at gene therapy, vehicles for gene delivery and other gene-editing strategies. There are several promising HSC gene therapies in the early phases of clinical trials, including treatments and products for sickle cell disease , X-linked forms of SCID, and Wiskott-Alrich Syndrome.

A clinical trial  that’s sponsored by the National Heart, Lung and Blood Institute in Maryland is currently recruiting pregnant women to examine the best ways to collect, process and store umbilical cord blood. For babies born with sickle cell disease, the blood collected from the cord and placenta will be stored indefinitely for use in gene therapy treatments later in life. For those babies born without sickle cell disease, the cord blood will be stored for up to 3 years and may possibly be used to treat living or future siblings who have, or may be born, with the disease.

In an attempt to treat both SCID and Wisckott-Alrich Syndrome, lentiviral genes are being used as vectors in Phase I/II trials. So far, there’s been with initial success in treating SCID in both older and younger patients. Likewise, in treating Wiskott-Alrich Syndrome, lentiviral therapy has proven both safe and effective.

Like all regenerative therapies, there are considerable obstacles to overcome and it takes time to research, develop, test, and regulate new products and methods. Nonetheless, over the last five decades, we’ve seen incredible advancements in HSC therapies that have helped doctors and patients treat and even cure several different disorders.

The hope, of course, is that successful clinical trials will lead to approvals by regulatory agencies, as was the case recently for Celixir’s own IND for Heartcl.  Eventually, researchers hope that these therapies will be adopted on a large scale by healthcare systems.

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