Patients with autoimmune destruction of hematopoietic cells frequently have severe and debilitating disease requiring aggressive and frequent medical management. These patients are often treated with non-specific immunosuppressive medications with limited efficacy and untoward side-effect profiles. We have been investigating the use of an immunosuppressive and anti-cancer agent, sirolimus in patients with an autoimmune cytopenias syndrome: Autoimmune Lymphoproliferative Syndrome (ALPS). ALPS is a primary immune deficiency caused by mutations in the Fas apoptotic pathway, leading to abnormal lymphocyte survival. Clinical manifestations in patients with ALPS typically include autoimmune cytopenias, lymphadenopathy, hepatosplenomegaly, and a propensity to develop secondary malignancies. Thus, far we have found excellent results albeit the total number of patients treated is small.