Objective: To determine if chronic motor deficits secondary to traumatic brain injury (TBI) can be improved by implantation of allogeneic modified bone marrow-derived mesenchymal stromal/stem cells (SB623).

Methods: This 6-month interim analysis of the 1-year double-blind, randomized, surgical sham-controlled, Phase 2 STEMTRA trial (NCT02416492) evaluated safety and efficacy of the stereotactic intracranial implantation of SB623 in patients with stable chronic motor deficits secondary to TBI. Patients in this multi-center trial (N=63) underwent randomization in a 1:1:1:1 ratio to 2.5x10⁶, 5.0x10⁶, 10x10⁶ SB623 cells or control. Safety was assessed in patients who underwent surgery (N=61), and efficacy in the modified intent-to-treat population of randomized patients who underwent surgery (N=61; SB623=46, control=15).

Results: The primary efficacy endpoint of significant improvement from baseline of Fugl-Meyer Motor Scale score at 6 months for SB623-treated patients was achieved. SB623-treated patients improved by (LS mean [SE]) +8.3 (1.4) versus +2.3 (2.5) for control at 6 months, the LS mean difference was 6.0 (95% CI: 0.3-11.8); P=0.040. Secondary efficacy endpoints improved from baseline, but were not statistically significant versus control at 6 months. There were no dose-limiting toxicities or deaths, and 100% of SB623-treated patients experienced treatment-emergent adverse events versus 93.3% of control patients (P=0.25).

Conclusions: SB623 cell implantation appeared to be safe and well tolerated, and patients implanted with SB623 experienced significant improvement from baseline motor status at 6 months compared to controls.

Classification of Evidence: This study provides Class I evidence that implantation of SB623 was well tolerated and associated with improvement in motor status.