Other than clinical observations, the stem cell field lacks a repeatable, time-sensitive, noninvasive tool to assess the effectiveness of transplanted cells in the targeted organ. Researchers analyzed biomarkers secreted from transplanted human stem cells in the recipient blood of a rodent model of heart attack. Analysis of the blood test showed responding cells had changed their gene expression, behavior and secretions, suggesting this liquid biopsy could provide a window into stem cell activity and effectiveness.