Background: Treatment of hemopoietic system neoplasias involves severecomplications associated with immunosuppression. We present two cases of treating severe sepsis utilizingrecombinant human activated protein C (rhAPC) in the course of bilateral pneumonia in patients with hairycell leukemia (HCL) and T-cell acute lymphoblastic leukemia (ALL). RhAPC, limited the coagulation cascadeby inactivating FVa and FVIIIa, directly and indirectly limiting systemic inflammatory response syndrome(SIRS), and improved the fibrinolysis process. These actions break the pathomechanism of sepsis and improvesurvival. Case Report: Besides intensive, multidirectional treatment of severe sepsis, Xigris (activateddrotrecogin alfa) was administered on the second day in both cases. The infusion continued, as recommended,for 96 hours without complications. During treatment the patients' general condition and respiratoryefficiency improved, allowing respirator weaning on days 5 and 8 of therapy. These cases of severe sepsisand immunosuppression indicate a high therapeutic efficacy of drotrecogin alfa (activated). Treatmentoutcome was uncertain because of the patients' hematological condition, so rapid restoration of respiratoryefficiency and no disease progression after discontinuing treatment was a great success, possibly dueto implementing Xigris at a relatively early stage of sepsis and the intensive therapy conducted accordingto Surviving Sepsis Campaign guidelines. Conclusions: Patient survival in severe sepsis directly dependson early diagnosis and institution of treatment. 1. These cases confirm the effectiveness of drotrecoginalfa in severe sepsis as part of multidirectional therapy. 2. Microorganisms causing atypical pneumoniashould be considered in diagnosing infections in patients treated with cytostatic agents.

Keywords: Leukemia, Lymphocytic, Acute - complications, Immune Tolerance, Leukemia, Hairy Cell - therapy, Precursor Cell Lymphoblastic Leukemia-Lymphoma - therapy, Protein C - therapeutic use, Recombinant Proteins - therapeutic use, Sepsis - drug therapy