(i) identifying a human subject suffering from persistent HSCT-TMA wherein said subject has TMA that persists despite a reduction or discontinuation of an immunosuppressive agent, or wherein said subject has TMA that persists at least 30 days after transplant; and

(ii) administering to the subject a composition comprising a MASP-2 inhibitory antibody, or antigen-binding fragment thereof, wherein the MASP-2 inhibitory monoclonal antibody or antigen-binding fragment thereof comprises a heavy chain variable region set forth as SEQ ID NO:67 and a light chain variable region set forth as SEQ ID NO:70, wherein the composition is administered at a dosage of at least 4 mg/kg at least once a week for a time period of at least three weeks, wherein said administration is effective to improve at least one or more of the following clinical parameters associated with persistent TMA associated with hematopoietic stem cell transplant: (i) an increase in platelet count (e.g., at least double, at least triple, at least quadruple the platelet count prior to treatment)); (ii) an increase in haptoglobin; (iii) a decrease in lactate dehydrogenase (LDH); and/or (iv) a decrease in creatinine.