Method - A nonviral gene transfer method for transfection multipotent adult progenitor cells (MAPC) Lakshmipathy U, Hammer L, Verfaillie C Multipotent adult progenitor cells (MAPC) are stem cells isolated primarily from adult bone marrow that have the ability to differentiate in vitro into cells with phenotypic and functional characteristics of cells from the three germ layers, namely endoderm, mesoderm and neuroectoderm. In addition, MAPCs proliferate for extended periods of time without obvious senescence. Hence, MAPCs may be ideal cells for therapy of genetic disorders, provided that the main impediment to gene therapy, namely efficient gene transfer and persistent gene expression, can be overcome. Most commercially available lipid-based methods that very highly efficiently transfect cell lines and primary cells, fail to transfect MAPC. However, 10–15% transfection of MAPC can be achieved using Superfect. However, this approach requires high density culture of MAPCs which subsequently differentiate. Between 12 and 15% transfection is achieved in MAPCs using electroporation, but this is highly toxic to MAPCs. Here, using transient expression of an enhanced green fluorescent protein (EGFP) gene, we report that nucleofection results in a transfection efficiency of over 25% with mouse MAPC without perturbing the conditions suitable for MAPC growth and maintenance, and with significantly less toxicity than electroporation. Similar results were seen for rat and human MAPC. Efficient transfection of MAPC by nucleofection offers an appealing non-viral mode of gene delivery and can be used to overexpress genes of interest in these cells. In addition, it should easily accomodate emerging site-specific integration technology, thereby culminating eventually in MAPC-mediated long-term gene therapy for genetic disorders.