BACKGROUND AND OBJECTIVE: Progress in medical sciences and technologies has made stem cells as a promising source of cell therapy of diseases. Many of researchers have focused on finding the optimum conditions for stem cell culture, to employ stem cells in cell therapy. Due to the capability of self-renewal and pluripotency, stem cells can give rise to progeny that either proliferate in an undifferentiated state or commit to a broad range of differentiated lineages, important for reconstruction of surrounding tissues. The adjacent microenvironment known as niche provides a complex molecular milieu that regulates the properties of stem cells in vivo. The main sources of stem cells contaminations will be discussed in this review.

METHODS: The present study is a literature search in PubMed, Science direct and Google scholar with the use of stem cells, microbial contamination and cell therapy as keywords. The results of animal and human studies published until 2012 in this field were considered.

FINDINGS: The main sources of stem cells contaminations include stem cell donor, feeder layer, animal sera, cell lines and environmental elements. Stem cells donors screening test, omission of feeder layer, application of serum replacements such as human serum albumin and optimization of cell culture conditions are some solutions to prevent stem cells contamination.

CONCLUSION: To maintain stem cells properties in vitro, it is necessary to simulate the niche in the cell culture which contains inevitably animal and human products, might be resulted in contamination of stem cells. These cells can carry the potential to induce xenogenic microchimerism in recipients or disease transmission through contamination with bacteria, viruses and other infectious agents.