Hematopoietic Stem Cell Transplantation

Bone marrow transplant (hematopoietic stem cell transplant) (HPSCT) involves the administration of healthy hematopoietic stem cells in patients with dysfunctional or depleted bone marrow. This helps to augment bone marrow function and allows, depending on the disease being treated, to either destroy tumor cells with malignancy or to generate functional cells that can replace the dysfunctional ones in cases like immune deficiency syndromes, hemoglobinopathies, and Other Diseases.

History and Evolution

Hematopoietic stem cell transplantation (HSCT) was first explored in humans in the 1950s and was based on observational studies in mice models which showed that infusion of healthy bone marrow components into a myelosuppressed bone marrow could induce recovery of its function in the recipient. These animal-based studies soon found their clinical application into humans when the first successful bone marrow transplant was performed in monozygotic twins in New York in 1957 (syngeneic transplant) in a patient with acute leukemia. As a result, the physician Dr. Thomas who performed the procedure continued his research on the development of bone marrow transplantation and later received the Nobel Prize of physiology and medicine in appreciation of his work. The first successful allogeneic bone marrow transplant was reported in Minnesota in 1968 for a pediatric patient with severe, combined immunodeficiency syndrome. Since then, allogeneic and autologous stem cell transplant has increased in the United States and worldwide. The Center for International Blood and Marrow Transplant Research (CIBMTR) reported over 8000 allogenic transplants performed in the United States in 2016 with a higher number of autologous transplants with a steady and higher increase of autologous compared to allogenic.

Definitions

Major Histocompatibility Complex (MHC)

The group of genes on the short arm of chromosome 6 (p6) that encodes human leukocyte antigens (HLA) which are considered being highly polymorphic leading to a large difference in the resultant expressed proteins on human cells. They are divided into MHC I and MHC II

Human Leukocyte Antigens (HLA)

These are the proteins expressed on the cellular surface and play an important role in alloimmunity. HLA can be divided into (HLA-A, B, and C) which are encoded by class I MHC and are expressed on all cell types and present Peptides derived from the cytoplasm and are recognized by CD8+ T cells. The other HLA type is classified as (HLA- DP, DQ, and DR) which are encoded by MHC II and can be found on antigen-presenting cells (APCs) and this class is recognized by CD4+ T cells.

Syngeneic Bone Marrow Transplantation

The donor and the recipient are identical twins. The advantages include no graft versus host disease (GVHD) and no graft failure. However, only a tiny number of transplant patients will have the ability to have an identical twin for transplantation.

Autologous Bone Marrow Transplantation

The bone marrow products are collected from the patient and are reinfused after purification methods. The advantages include no GVHD. The disadvantage is that the bone marrow products may contain abnormal cells that can cause relapse in the case of malignancy hence; theoretically, this method cannot be used in all cases of abnormal bone marrow diseases.

Allogenic Transplantation

The donor is an HLA matched family member, unrelated matched donor or mismatched family donors (haploidentical).

Engraftment

The process of which infused transplanted hematopoietic stem cells produce mature progeny in the peripheral circulation

Preparative Regimen

This is a regimen that comprises high-dose chemotherapy and/or total body irradiation (TBI) which are administered to the recipient prior to stem cell infusion to eliminate the largest number of malignant cells and to allow for immunosuppression in the recipient so that engraftment can occur.