Aplastic anemia in younger patients is generally an immune disorders, in which the immune system attack newly forming red cells and kills them. For this reason, it is often treated with immunosuppression. The risks of supressing the immune system is greater in older people, and for this reason, the suppression of the immune system is more often used in younger patients. Older individuals and those who failed immune suppressing drugs, should go on to stem cell transplantation. When there is no sibling donor, cyclosporine(CSA) is recommended, usually in combination with other drugs but it can also be used alone. First-line treatment approaches include immunosuppressive treatment using the combination of antithymocyte globulin and cyclosporine A for patients without a sibling donor and HLA identical sibling transplant for patients younger than age 40 with a donor. Despite a theoretical rationale for its use, sirolimus did not improve the response rate in patients with severe aplastic anemia when compared to standard h-ATG/CsA.