Stem cell transplantation is an important avenue for SCI research: the goal is to replace lost spinal cord cells, allow reconnection in broken neural circuits by regrowing axons, and to create an environment in the tissues that is favorable to growth. A key avenue of SCI research is research on stem cells, which can differentiate into other types of cells—including those lost after SCI. Types of cells being researched for use in SCI include embryonic stem cells, neural stem cells, mesenchymal stem cells, olfactory ensheathing cells, Schwann cells, activated macrophages, and induced pluripotent stem cells. Hundreds of stem cell studies have been done in humans, with promising but inconclusive results. An ongoing Phase 2 trial in 2016 presented data showing that after 90 days, 2 out of 4 subjects had already improved two motor levels and had thus already achieved its endpoint of 2/5 patients improving two levels within 6–12 months. Six-month data is expected in January 2017.