We plan to confirm our hypotheses by performing a pilot series in children with autoimmune cytopenias who are either refractory to standard therapy or have significant toxicity from standard treatments. Our primary aim is to define the toxicities of administration of oral sirolimus in children with autoimmune cytopenias. Our secondary aims are to evaluate the efficacy of sirolimus in children with autoimmune cytopenias, to determine the trough levels of sirolimus when used in these patients, and to evaluate the effects of sirolimus on intracellular targets of mammalian target of rapamycin (mTOR). We intend to enroll 50 children with autoimmune cytopenias and treat for a 6 month period, however, if we find sirolimus is effective, we anticipate these children will continue to take sirolimus for a longer period of time. We anticipate the results of this work will establish sirolimus is an effective and well tolerated medication and will lead directly to a larger national phase II clinical trial.