Response by Steinberg et al to Letter Regarding Article, “Clinical Outcomes of Transplanted Modified Bone Marrow–Derived Mesenchymal Stem Cells in Stroke: A Phase 1/2A Study”

We thank Dr Clark for his comments. Immunomodulation related to protein and molecular factors secreted by the SB623 cells could be one of the mechanisms underlying the observed neurological recovery in our patients1 and could suggest that there is ongoing chronic inflammation >6 months after stroke that is suppressing intact neural circuits and rendering them nonfunctional. This concept has some support in the recent preclinical and clinical literature.2 In addition, it is conceivable that the transplanted SB623-secreted factors are enhancing native neurogenesis or synaptogenesis, potentially through blocking excess tumor necrosis factor effects after stroke, although this is unproven. It will be important …