Fig. 1: Experimental design schematic.

a Quantitative innate immune cell profiling in the presence of PLG bridge following SCI. Schematic shows C5 hemisection injury and implantation of PLG bridge at the lesion site. C4 to C6 spinal cord segments (injury at C5) were dissected at the following time points post-injury, 1 day post-injury (DPI), 1 week post-injury (WPI), 4 WPI, 8 WPI, and 24 WPI. Dissected spinal cord tissues were processed for flow cytometric analysis to quantify innate immune cell profiling in C57BL/6 (Fig. 2) and Rag1 (Supplemental Fig. 2) mice. b In vitro analysis of PLG scaffold and innate immune cues on hNSC cell fate. Polymorphonuclear neutrophils (PMN) and macrophages (MØ) were isolated from the peritoneal cavity of Rag1 immunodeficient mice stimulated with 12% sodium caseinate (i.p.). PMN and MØ were subsequently cultured in hNSC differentiation medium (DM), and respective conditioned media (PMN-CM, MØ-CM) was collected. hNSC were differentiated on PLO/LAM (control substrate) and PLG scaffold in the presence of DM, PMN-CM, and MØ-CM. hNSC fate was quantified using Imaris software following immunocytochemistry. c Timeline for the combinatorial approach of PLG bridge implantation and hNSC transplantation in Rag1 immunodeficient mice. Mice received a C5 left hemisection injury with immediate PLG bridge implantation and coverage of the dorsal surface with gel foam; SCI control mice received only gel foam. 4 WPI, mice received either vehicle injection or hNSC transplantation into the spared tissue parenchyma at four sites, two rostral and two caudal to the lesion site. Mice were randomly distributed into SCI control vs. PLG bridge groups at the time of initial surgery, and into the vehicle vs. hNSC groups on the day of transplantation. hNSC fate and distribution, host axonal regeneration, myelination status, and locomotor recovery were analyzed at 16 weeks post-transplantation (WPT). Finally, transsynaptic PRV retrograde tracing was performed at 26 WPT (30 WPI) to investigate synaptic connectivity of regenerated axons.