Chapter 23: Haemopoietic Stem Cell Transplantation

Haemopoietic Stem Cell Transplantation vital cells are harvested from three primary sources: peripheral blood via apheresis after being mobilized from the marrow using growth factors, directly from the pelvic bone marrow under general anesthesia, or from umbilical cord blood, which is particularly useful for pediatric cases due to the immunological flexibility of the cells. Donor selection is categorized as autologous when using the patient's own stored cells, syngeneic for identical twins, or allogeneic when utilizing related or unrelated donors matched via the human leucocyte antigen system. Located on chromosome six, the human leucocyte antigen complex—comprising Class One and Class Two molecules—serves as the primary determinant of tissue compatibility; a significant mismatch here drastically increases the likelihood of graft failure or immune rejection. Prior to the infusion, patients undergo conditioning regimens, which may be myeloablative to completely eradicate the host's existing marrow and underlying malignancy using high-dose chemotherapy and total body irradiation, or reduced-intensity to provide sufficient immunosuppression for older or more fragile individuals. While autologous transplantation is frequently utilized to treat multiple myeloma and lymphoma by allowing the delivery of intensive therapy that would otherwise cause permanent marrow failure, allogeneic transplantation is a cornerstone for treating acute leukaemias, myelodysplastic syndromes, and severe bone marrow failure. A critical therapeutic component of the allogeneic process is the graft-versus-leukaemia effect, where donor immune cells recognize and destroy residual malignant cells, a mechanism that can be deliberately boosted post-transplant through donor leucocyte infusions. The success of the engraftment is often monitored through chimerism analysis, which determines the ratio of donor to recipient cells in the blood. However, this same immunological activity can lead to graft-versus-host disease, a major complication where donor T cells attack the recipient's skin, liver, and gastrointestinal tract. Management of these patients requires intensive supportive care to mitigate risks during the period of severe blood count depletion, including rigorous monitoring for opportunistic fungal infections and viral reactivations such as cytomegalovirus. Long-term recovery is further challenged by the potential for disease relapse, late-onset organ toxicities, and the development of post-transplant lymphoproliferative disease, often driven by the Epstein-Barr virus in the context of chronic immunosuppression.