This is a double-armed, Phase I/II trial aims to compare bone marrow and leukapheresis as sources for purified, autologous CD34+ and CD133+ stem cells (SCs), to be utilized in treatment of patients with chronic complete spinal cord injuries (SCI). The study focuses on the safety and efficacy of transplanting un-manipulated, autologous, purified stem cells into the injured spinal cords of patients.