Bone marrow is the source of all blood cells. While most diseases have some genetic component, the term genetic disease is usually applied to those cases where one or two genes determine the disease, such as sickle cell anemia, Tay Sachs disease, and cystic fibrosis. These molecules have a role in regulating the immune response in general. There is a correlation between certain HLA antigens and certain diseases such that people with those HLA antigens are at higher risk for those diseases. These are the autoimmune, allergic, and immunodeficiency diseases.
Immunosuppression is the treatment for graft rejection and autoimmune disease.
Nearly all organ and bone marrow transplants are allografts. These may be between brothers and sisters, parents and children, or between donors and recipients who are not related to each other.