Cytokine Polarized Bone Marrow Neutrophils Drive Axon Regeneration

The adult central nervous system (CNS) has a limited capacity for self-repair. Severed CNS axons typically do not regrow. There is an unmet need for treatments specifically designed to enhance neuronal viability, facilitate CNS axon regeneration, and ultimately restore lost neurological functions to individuals with traumatic CNS injury, multiple sclerosis, and stroke, among other disorders. Here we demonstrate that both mouse and human bone marrow (BM) neutrophils upregulate markers of alternative activation, and acquire the ability to promote neurite outgrowth, following polarization with a combination of recombinant interleukin-4 (IL-4) and granulocyte-colony stimulating factor (G-CSF). Moreover, adoptively transferring IL-4/G-CSF polarized BM neutrophils into experimental models of CNS injury resulted in significant axon regeneration within the optic nerve and spinal cord. The findings reported in this paper hold significant implications for the future development of autologous myeloid cell-based therapies that may bring us closer to effective solutions for reversing CNS damage. To investigate the effect of polarization on the generation of alternatively activated immune cells, mouse Ly6G+ bone marrow neutrophils and human CD34+ bone marrow cells were polarized with or without IL-4 and/or G-CSF.