Nuclear reprogramming with a non-integrating human RNA virus

Introduction: Advances in the field of stem cells have led to novel avenues for generating induced pluripotent stem cells (iPSCs) from differentiated somatic cells. iPSCs are typically obtained by the introduction of four factors-OCT4, SOX2, KLF4, and cMYC-via integrating vectors. Here, we report the feasibility of a novel reprogramming process based on vectors derived from the non-integrating vaccine strain of measles virus (MV). Methods: We produced a one-cycle MV vector by substituting the viral attachment protein gene with the green fluorescent protein (GFP) gene. This vector was further engineered to encode for OCT4 in an additional transcription unit. Results: After verification of OCT4 expression, we assessed the ability of iPSC reprogramming. The reprogramming vector cocktail with the OCT4-expressing MV vector and SOX2-, KLF4-, and cMYC-expressing lentiviral vectors efficiently transduced human skin fibroblasts and formed iPSC colonies. Reverse transcription-polymerase chain reaction and immunostaining confirmed induction of endogenous pluripotency-associated marker genes, such as SSEA-4, TRA-1-60, and Nanog. Pluripotency of derived clones was confirmed by spontaneous differentiation into three germ layers, teratoma formation, and guided differentiation into beating cardiomyocytes. Conclusions: MV vectors can induce efficient nuclear reprogramming. Given the excellent safety record of MV vaccines and the translational capabilities recently developed to produce MV-based vectors now used for cancer clinical trials, our MV vector system provides an RNA-based, non-integrating gene transfer platform for nuclear reprogramming that is amenable for immediate clinical translation.