Stem/precursor cell-based CNS therapy: the importance of circumventing immune suppression by transplanting autologous cells.

Stem/precursor cell (SPC) therapy for neurodegeneration and neurotrauma has enormous therapeutic potential, but despite ongoing research efforts the success of clinical trials remains limited. Therapies that utilize immune suppression in combination with SPC transplantation have thus far failed to consider the beneficial role of the immune system in central nervous system (CNS) recovery. Systemic immune suppression may prevent neural repair, and in some cases exacerbate the underlying disorder. Until about a decade ago, immunosuppression for CNS disorders was viewed as a therapeutic target, based on the perception that all immune activity in the CNS was destructive. However, recent studies show that the infiltration of blood-borne immune cells into the CNS following neurotrauma and during chronic neurodegeneration promote CNS protection and regeneration. In the context of SPC therapies, although immune suppression prevents rejection of non-autologous cell grafts, it also prevents the restorative immune response by eliminating the immune mediated guidance cues that are required for SPCs to migrate to the location they are needed, and preventing SPC-mediated immunomodulation. This article argues in favor of transplanting autologous SPCs, particularly bone marrow derived cells. The therapeutic use of autologous SPCs for neural repair circumvents the need for concomitant immune suppression, exploits the immunomodulatory capacity of these cells, and maintains the immune niche that supports neural repair and is required to guide these cells to their appropriate locations. Overall, such an approach accommodates the requirements for translational therapeutics, and provides a standardized platform for reconciling the inherent controversies in the science.