instruction: how many patients died before 2155 and followed the procedure allogeneic hematopoietic stem cell transpant without purging?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN procedures ON demographic.hadm_id = procedures.hadm_id WHERE demographic.dod_year <= "2155.0" AND procedures.long_title = "Allogeneic hematopoietic stem cell transpant without purging"