A therapy for complete spinal cord injury (SCI) is being developed, consisting of autologous grafts of macrophages that have been educated to a wound-healing phenotype by co-incubation with skin tissue. Following successful Phase I clinical trials that indicated a favorable safety profile, the therapy is now being tested in Phase II clinical trials. The purpose of this study was to test the potential safety and efficacy of this therapy in cases of initial white matter sparing (incomplete SCI).

The effect of skin-coincubated macrophages on the survival of intact spinal cord fibers was examined in adult rats subjected to  moderate spinal cord contusion at the T9 level, then injected with macrophages or cell-free medium 8-9 post injury. Fluorogold retrograde tracing experiments three months later revealed higher numbers of labeled neurons in red nuclei of the macrophage-treated rats, indicating enhanced neuronal survival. Behavioral assessment revealed significantly better recovery in the macrophage-treated rats.

The safety of the administration procedure was tested by multiple injections of cell-free medium into the intact porcine spinal cord, using a protocol similar to that used in clinical trials. Different volumes were delivered in six injections at each of two levels, C6 and T10. The animals were followed clinically for 28 days, at the end of which no residual clinical abnormalities were observed. The animals were then sacrificed, and the spinal cords were removed and subjected to histopathological analysis. This revealed only minor, localized tissue abnormalities, apparently due to needle penetration and not related to the injected volume

These results indicate that neither therapeutic macrophages nor the delivery mechanism should pose a threat to spinal nerve fibers that have survived trauma. Thus the macrophage cell therapy now being tested on patients with complete SCI may also be beneficial in cases of incomplete SCI, which account for slightly over 50% of all SCI cases.