3D ECM-rich environment sustains the identity of naive human iPSCs.

The establishment of in vitro naive human pluripotent stem cell cultures opened new perspectives for the study of early events in human development. The role of several transcription factors and signaling pathways have been characterized during maintenance of human naive pluripotency. However, little is known about the role exerted by the extracellular matrix (ECM) and its three-dimensional (3D) organization. Here, using an unbiased and integrated approach combining microfluidic cultures with transcriptional, proteomic, and secretome analyses, we found that naive, but not primed, hiPSC colonies are characterized by a self-organized ECM-rich microenvironment. Based on this, we developed a 3D culture system that supports robust long-term feeder-free self-renewal of naive hiPSCs and also allows direct and timely developmental morphogenesis simply by modulating the signaling environment. Our study opens new perspectives for future applications of naive hiPSCs to study critical stages of human development in 3D starting from a single cell.

Microfluidic reprogramming to pluripotency of human somatic cells.

Human induced pluripotent stem cells (hiPSCs) have a number of potential applications in stem cell biology and regenerative medicine, including precision medicine. However, their potential clinical application is hampered by the low efficiency, high costs, and heavy workload of the reprogramming process. Here we describe a protocol to reprogram human somatic cells to hiPSCs with high efficiency in 15 d using microfluidics. We successfully downscaled an 8-d protocol based on daily transfections of mRNA encoding for reprogramming factors and immune evasion proteins. Using this protocol, we obtain hiPSC colonies (up to 160 ± 20 mean ± s.d (n = 48)) in a single 27-mm2 microfluidic chamber) 15 d after seeding ~1,500 cells per independent chamber and under xeno-free defined conditions. Only ~20 µL of medium is required per day. The hiPSC colonies extracted from the microfluidic chamber do not require further stabilization because of the short lifetime of mRNA. The high success rate of reprogramming in microfluidics, under completely defined conditions, enables hundreds of cells to be simultaneously reprogrammed, with an ~100-fold reduction in costs of raw materials compared to those for standard multiwell culture conditions. This system also enables the generation of hiPSCs suitable for clinical translation or further research into the reprogramming process.