A bone marrow transplant is a replacement of bone marrow with healthy cells. It is also called a stem cell transplant or hematopoietic stem cell transplant. It treats cancer, such as lymphoma, leukemia, myeloma, and other blood and immune system diseases that affect the bone marrow. There are different types of bone marrow transplants such as Autologous transplants, Allogenic transplants, Umbilical cord blood transplants, and Haploidentical transplants. Healthy blood-forming cells used in transplant comes from 3 sources Bone marrow, Peripheral blood stem cells (PBSC), and Cord blood. After a bone marrow transplant sometimes the body’s immune system treats the new organ like a foreign object and attacks the transplanted organ or tissue. There are three types of rejection like Hyperacute rejection, Acute rejection, and Chronic rejection. Some medicines are used to prevent organ rejection in bone marrow transplants. These medicines are called immunosuppressants (anti-rejection drugs)