Mesenchymal stem cells (MSCs) are multipotent cells found in both fetal and adult tissues. MSCs show promise for cellular therapy for several disorders such as those associated with inflammation. In adults, MSCs primarily reside in the bone marrow (BM) and adipose tissues. In BM, MSCs are found at low frequency around blood vessels and trabecula. MSCs are attractive candidates for regenerative medicine given their ease in harvesting and expansion and their unique ability to bypass the immune system in an allogeneic host. Additionally, MSCs exert pathotropism by their ability to migrate to diseased regions. Despite the “attractive” properties of MSCs, their translation to patients requires indepth research. “Off-the-shelf” MSCs are proposed for use in an allogeneic host. Thus, the transplanted MSCs, when placed in a foreign host, could receive cue from the microenvironment for cellular transformation. An important problem with the use of MSCs involves their ability to facilitate the support of breast and other cancers as carcinoma-associated fibroblasts. MSCs could show distinct effect on each subset of cancer cells. This could lead to untoward effect during MSC therapy since the MSCs would be able to interact with undiagnosed cancer cells, which might be in a dormant state. Based on these arguments, further preclinical research is needed to ensure patient safety with MSC therapy. Here, we discuss the basic biology of MSCs, discuss current applications, and provide evidence why it is important to understand MSC biology in the context of diseased microenvironment for safe application. 1. Introduction Stem cell therapy is not a new field but should be considered as an expanded field to successful bone marrow transplantation for several disorders such as autoimmune diseases and hematological malignancies. Decades of clinical application to reconstitute the hematopoietic system have led to improved methods to increase the age for transplants, resulting in benefit to an aging population [1, 2]. The long history of a focus on hematopoietic stem cells resulted in scientists overlooking other organs with tissue-specific stem cells. This past decade corrected this oversight, resulting in an “explosion” in the number of papers, journals, and scientific meetings on stem cells. The new focus correlated with an increase in registered stem cell clinical trials (clinicaltrials.gov). Those involved in the educational system across the globe are aware that stem cells are moving rapidly to the clinic while the education of future scientists and practicing physicians lags.
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