Hemophagocytic lymphohistiocytosis (HLH) is a rare immunological disorder first recognized almost 70 years ago.(1) Genetic and animal studies have indicated that the familial form of HLH is clearly due to a deficiency of cytotoxic killing. Patients with HLH present with a potentially fatal syndrome of 'hyperimmunity.' These patients have severe inflammation, associated with cytopenias and variably severe bone marrow, liver, or CNS damage. Tissue damage and mortality appear to be due to hypercytokinemia related to persistent immune hyperactivation. An animal model of HLH and correlative human studies all suggest that excessive and abnormal activation of T cells drives the pathophysiology of this disorder, and that suppressing this excessive activation is critical for successful therapy of HLH. It is believed a combination of the two proven induction regimens for hemophagocytic lymphohistiocytosis (HLH) (anti-thymocyte globulin (ATG)- and etoposide-based) will result in response rates and overall survival rates at eight weeks which are comparable or better than the current standard of care (induction therapy per the HLH-94 protocol).