What Is Hematopoietic Stem Cell Transplantation?

Introduction

Within the human body, cells are abounding, with there being about 37 trillion cells that form the human body and that have a range of functions necessary for our survival.^{1, 2} Among these cells are hematopoietic stem cells (HSCs), are a type of cell that can give rise to any of the cells of the blood. Typically, HSCs are found in blood and bone marrow, where they mature into blood cells and can then enter the bloodstream.³ These components of blood play a crucial role in the human body and include platelets, which help prevent bleeding; red blood cells, which deliver oxygen to organs so they can function and carbon dioxide to the lungs so it can be expelled from the body, and white blood cells, of which there are several, that help the body fight off infections.^{4, 5}

Sometimes, bone marrow is dysfunctional, which can result in a range of diseases. It is said in cases that hematopoietic stem cell transplantation (HSCT), also known as bone marrow transplantation, may be a helpful treatment. HSCT involves transferring healthy HSCs to patients with dysfunctional bone marrow. The first successful HSCT was performed in 1957 to treat leukaemia, and, since then, HCST has become increasingly utilised as a therapy.⁶

Types of hematopoietic stem cell transplantation

There are two types of HCST: autologous and allogeneic. Autologous HSCT involves transplanted HSCs initially being collected from the same patient who will receive these. Allogeneic HSCT involves stem cells being collected from a donor who is distinct from the patient receiving these. Whether autologous or allogeneic, the HSCs are typically sourced from the bloodstream and then implanted into the patient’s bone marrow or bloodstream to treat a disease or restore the production of blood cells to normality.^{7, 8}

Indications for hematopoietic stem cell transplantation

HSCT can be used in the treatment of various diseases. Typically, these disorders are characterised by dysfunction of the blood cells or bone marrow, which produces the blood cells. Listed below are several of the conditions that can be treated with HSCT.⁸ 

Leukaemia

There are different forms of leukaemia, and acute myeloid leukaemia, acute lymphoblastic leukaemia, chronic myeloid leukaemia, and chronic lymphocytic leukaemia are among those that can be treated with HSCT. Leukaemia is characterised by abnormal white blood cells being excessively produced. How the condition presents can vary with the subtype. Signs and symptoms of leukaemia can include tiredness, weight loss, bone pain, and increased bleeding and bruising. HSCT combined with other therapies can treat the condition.^{8, 9}

Myelodysplastic syndromes

Myelodysplastic syndromes comprise diseases characterised by the disturbed development of HSCs into cells of the blood. Typically, these conditions occur in the elderly, but how myelodysplastic syndromes present can vary a lot from patient to patient, with survival rates ranging from a few months to many years. Patients with this condition are at an increased risk of having leukaemia, specifically acute myeloid leukaemia. However, up to half of the patients with these conditions who receive HSCT are cured with the therapy.¹⁰

Myeloproliferative neoplasms

Myeloproliferative neoplasms are disorders of HSCs where HSCs develop more rapidly into certain cells of the blood. The elderly tend to be the most affected by these conditions. Myeloproliferative neoplasms can reduce life expectancy due to complications of the condition, such as thromboses, haemorrhages, and organ damage, but treatment, such as HSCT, can combat this.¹¹

Anaemia

Anaemia is a condition caused by low numbers of red blood cells or haemoglobin, that being a protein that transports red blood cells in the blood as a means of delivering oxygen to organs so that these organs can function. Anaemia can commonly cause weakness, tiredness, restless legs, breathlessness, chest pain, and coolness and paleness of the skin. There are various forms of anaemia which vary depending on their cause, but those that may be able to be treated with HSCT include aplastic anaemia, Fanconi’s anaemia, Blackfan-Diamond anaemia, and sickle cell anaemia.^{12, 13}

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is a rare condition caused by the failure of the bone marrow to function properly in producing blood cells. It can cause a lack of red blood cells, anaemia, and thrombosis. Signs and symptoms include tiredness, breathlessness, and abdominal pain. Patients with this condition are much more likely to be diagnosed with kidney disease. However, HSCT can help effectively treat the condition.¹⁴

Hematopoietic stem cell transplantation procedure

The NHS describes HSCT as having five main stages:

1. Tests and examinations: These assess your general health.
2. Harvesting: This is the process of HSCs, which will later be transplanted into a patient, being collected, either from that same patient, in the case of autologous HSCT, or from a donor distinct to the patient, in the case of allogeneic HSCT.
3. Conditioning: This is treatment with chemotherapy or radiotherapy to prepare you for HSCT.
4. Transplantation: The harvested HSCs are transplanted into the patient.
5. Recovery: You will have to remain in the hospital for at least a few weeks for the HSCT to take effect.

Risks of hematopoietic stem cell transplantation

Though HSCT can be a life-saving treatment for many patients, HSCT can carry several significant risks both in the short-term and long-term. Patients who receive HSCT are at an increased risk for cardiovascular disease, diabetes, an underactive thyroid, weakened bones, certain cancers, and reproductive difficulties in the long term. Below are the key complications of HSCT, which were discussed in more detail.^7,15

Graft-versus-host disease 

Graft-versus-host disease is specifically a risk of allogeneic HSCT. It occurs as a result of the transplanted HSCs recognising the patient as a foreign body and thus fighting against it, resulting in the disease. Typically, the skin, liver, and gastrointestinal system are impacted by this condition and commonly it causes nausea, vomiting, diarrhoea, weight loss, yellowing of the skin, and a rash.⁷

Infections

Infections are a risk throughout the stages of HSCT. These infections can impact various parts of the body depending on the organisms that cause them and can cause a range of signs and symptoms which can vary from patient to patient depending on the specific infection that they have.^{7, 15} 

Relapses of underlying disease

The success of HSCT can vary from patient to patient and depending on a patient’s particular disease. Sometimes, the disease that HSCT is treating can recur after this therapy; the risk of this happening varies for different diseases.⁷

FAQs

Who can be a donor for hematopoietic stem cell transplantation?

Successful allogeneic HSCT requires a donor having HSCs that carry a marker, called human leukocyte antigen, that is identical or similar to the patient receiving those HSCs. Siblings of said patients are typically most likely to have HSCs suitable for the patient receiving HSCT. However, potential matches can also be sourced from registries with other donors. Donating HSCs should be excluded if donors’ health is at excessive risk, which can be established by consulting with your doctor.¹⁶

How long does it take to recover from hematopoietic stem cell transplantation?

Recovery following HSCT can vary from patient to patient. Typically, patients need to remain in the hospital for at least a few weeks following HSCT for the treatment to take effect. Complications can prolong this recovery time.^{7 15}

Can hematopoietic stem cell transplantation be repeated if needed?

Sometimes, due to complications, a second HSCT may be performed.^{17, 18, 19}

Summary

Hematopoietic stem cell transplantation (HSCT), also known as a bone marrow transplant, is a procedure that involves the transfer of hematopoietic stem cells (HSCs), those being cells that can develop into blood cellsinto a patient whose blood cells are, or how they are produced is, dysfunctional, which may be due to various diseases. HSCT can be autologous or allogeneic, the former meaning that HSCs are collected from the same patients who will receive them and the latter meaning that HSCs are collected from a donor who is distinct from the patient receiving them. HSCT typically involves five stages, these being tests and examination to assess general health, harvesting of HSCs, conditioning to prepare a patient for HSCT, transplantation of HSCs, and a recovery period which involves a stay of at least a few weeks in the hospital as the HSCT takes time to take effect. HSCT can cause complications, including graft-versus-host disease, infections, and relapses of underlying disease. Ultimately, however, HSCT can treat several diseases and save lives.