This clinical trial is being conducted by the University of Texas in Houston. The aim of this trial is to determine the effect of the patient’s own bone marrow on limiting the extent of the resultant neurological impairment following severe traumatic brain injury. The study seeks to enrol 20 participants within 24 hours of their brain injury. Participants will have a Coma Score of between 5 and 6. The first five participants will receive only the conventional treatment for severe brain injury. The second five will be given cells taken from their bone marrow (via IV). The next two groups of five patients will each receive a progressively increasing dose of the bone marrow cells - to determine if the number of bone marrow cells infused has a role. Participants will be assessed for complications and any change in their Coma Score or other disability ratings. The trial is expected to be completed by June 2014.