Delayed transplantation of neural stem cells improves initial graft survival following stroke

Neural stem cell therapies hold great promise for improving stroke recovery, but the hostile stroke microenvironment can hinder the initial graft survival. It has long been well documented that the microenvironment evolves over time, making it crucial to identify the optimal transplantation window to maximize therapeutic efficacy. However, it remains uncertain whether acute or delayed local cell transplantations better supports graft viability after stroke. Here, we show that delayed intracerebral transplantation of neural progenitor cells (NPCs) derived from human induced pluripotent cells (iPSCs) at 7 days post stroke significantly enhances graft proliferation and survival, compared to acute transplantation at 1 day post stroke, in a mouse model of large cortical stroke. Using in vivo bioluminescence imaging over a 6-week period post-transplantation, we observe a more than 5-fold increase in bioluminescence signal in mice that received delayed NPC therapy, compared to those that underwent acute NPC transplantation. The increased number of cell grafts in mice receiving delayed NPC transplantation was driven by increased proliferation rates early after transplantation, which subsequently declined to similarly low levels in both groups. Notably, we found that the majority of transplanted NPCs differentiated into neurons after 6 weeks, with no significant differences in the neuron-to-glia ratio between acute and delayed transplantation groups. These findings suggest that delayed NPC transplantation improves early graft survival and proliferation, which could help identify the optimal therapeutic window for maximizing the effectiveness of NPC-based therapies in stroke.