Allogeneic Stem Cell Transplantation is a medical procedure where stem cells are taken from a healthy donor and transplanted into a patient. This treatment is often used for conditions like leukemia, lymphoma, and other blood disorders. The goal is to replace damaged or diseased bone marrow with healthy stem cells, which can produce new blood cells. The donor's stem cells can come from various sources, including bone marrow, peripheral blood, or umbilical cord blood. Before the transplant, the patient usually undergoes chemotherapy or radiation to prepare their body. This process helps the new stem cells to engraft and start producing healthy blood cells.