Mesenchymal stromal cells and fibroblasts: a case of mistaken identity?

The plastic-adherent fibroblast-looking cells that can be isolated and culture-expanded from bone marrow and many other tissues are widely known as mesenchymal stromal cells (MSC). In addition to their fibroblast-like morphology, they are characterized by a panel of cell-surface markers and their potential to differentiate into bone, fat and cartilage. Based on their intriguing immunomodulatory and regenerative properties, MSC are being investigated as cellular therapeutics for a variety of clinical indications. However, many questions regarding the true identity and functionality of these cells in vivo remain unanswered. Fibroblasts, known for a much longer time but still poorly characterized, are also considered to be a ubiquitous stromal element of almost all tissues and are believed to play a role in tissue homeostasis. Despite the presence of MSC and fibroblasts in almost all tissues, similar morphology and other shared characteristics, the exact relationship between MSC and fibroblasts has remained undetermined. In this review, based on recent and old, but often neglected, literature it is suggested that ex vivo culture-expanded MSC and fibroblasts are indistinguishable by morphology, cell-surface markers, differentiation potential and immunologic properties.