Allogeneic stem cell transplantation is a medical procedure where stem cells are taken from a healthy donor and given to a patient. This treatment is often used for conditions like leukemia or lymphoma, where the patient's own bone marrow is damaged or diseased. The donor's stem cells help to rebuild the patient's blood and immune system. The process involves matching the donor and recipient to reduce the risk of complications. After the transplant, the patient may need to take medications to prevent the body from rejecting the new cells. Successful transplants can lead to long-term remission and improved health.