Patients, ages18 to 55 years old, admitted to Memorial Hermann Hospital Trauma Center with Glasgow Coma Scores (GCS) of 5 to 8 will be screened. Those patients meeting inclusion/exclusion criteria (or their Legal Authorized Representative [LAR]) will be offered consent to participate. This is a dose-escalation study consisting of 4 cohorts including a control group (5 subjects/cohort). The first five subjects will not undergo the bone marrow harvest procedure; though they will be followed and treated the same as the other study participants and complete all follow-up procedures. Subjects 6-10 will receive the lowest dose target of 6X106 mononuclear cells/kilogram body weight. Subjects 11-15 will receive 9x106 mononuclear cells/kilogram body weight, and lastly Subjects 16-20 will receive 12X106 mononuclear cells/kilogram body weight. The study is NOT powered to detect functional measures of efficacy. However, estimates can be made regarding potential treatment effect sizes to allow rational power analyses for the follow-on Phase II study. This study should determine if bone marrow harvest, BMMNC separation, and reinfusion is safe in adults with acute, severe TBI.