Inclusion Criteria:  Patients must have clinically definite ALS (Awaji Criteria) Male or female age 18 years and less than 75 years at time of ALS study Symptom onset less than 36 months before screening Diagnosis of ALS less than 24 months before screening Clinically definite Upper Motor Neuron signs  Exclusion Criteria:  Current treatment with anticoagulants (e.g., warfarin, novel oral anticoagulants, heparin) that might preclude safe completion of the lumbar puncture Condition that precludes the safe performance of routine lumbar puncture, such as prohibitive lumbar spinal disease, bleeding diathesis, or clinically significant coagulopathy or thrombocytopenia Use of investigational drugs or devices within 60 days prior to Baseline (dietary supplements taken outside of a clinical trial are not exclusionary, e.g., coenzyme Q10) Prolonged prothrombin time or activated partial thromboplastin time >2xULN Severe hypertension or hypotension Glomerular filtration rate (GFR) <35 mL/min Forced vital capacity (FVC) at screening of <50% of predicted Prior exposure to any exogenous form of APC Inability to lie flat for procedures (MRI, PET, LP) Pregnant or lactating during the study period