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CD341 adipose stromal cells are scattered in the adipose tissue and found in the CD341 population of the stromal vascular fraction (SVF). This fraction includes adipose-derived stromal/stem/progenitor cells (ASCs), which have attracted considerable attention and show great promise for the future of regenerative medicine. Studies in this field have been undertaken mainly in vitro. In this work, however, we assessed the characteristics of human adipose tissue-resident CD341 stromal cells in normal conditions and when activated in vivo during inflammatory/repair processes at different stages of evolution. In normal adipose tissue, these cells showed a characteristic location (peri/paravascular and between adipocytes), a fusiform or stellate morphology, long and moniliform processes, and scarce organelles. During inflammatory/repair stages, native CD341 stromal cells increased in size, proliferated, developed numerous organelles of synthesis, lost CD34 expression, and differentiated into myofibroblasts (aSMA expression and typical ultrastructure). In double-stained sections, cells expressing both CD34 and aSMA were observed. CD34 expression correlated positively with a high proliferative capacity (Ki-67 expression). Conversely, CD34 expression was lost with successive mitoses and with increased numbers of macrophages in the granulation tissue. CD341 stromal cell behavior varied depending on proximity to (with myofibroblast differentiation) or remoteness from (with activated plump cells conserving CD34 expression) injury. In conclusion, our observations point to human adipose tissue-resident CD341 stromal cells as an important source of myofibroblasts during inflammatory/ repair processes. Moreover, stromal cell activation may occur with or without aSMA expression (with or without myofibroblast transformation) and with

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