Amanda Haupt, is a senior scientist and R&D project manager at Horizon Discovery, a PerkinElmer Company. During her years with the company, she has contributed to the development of the broad portfolio of gene editing and gene modulation reagents. Today, Amanda works with cross-functional teams to launch innovative new products and services within the research reagents, cell line engineering, and screening divisions of Horizon Discovery. Before joining Horizon, Amanda worked at the Allen Institute for Cell Science in Seattle, WA, where she contributed to the generation of the Allen Cell Collection of endogenously tagged iPSC lines.
Because they are renewable in culture, amenable to gene correction, derived from both patients and controls, and capable of differentiating into any cell type, human induced pluripotent stem cells (iPSCs) are uniquely positioned to revolutionize the fields of gene therapy and regenerative medicine. While many hurdles remain along the path to the clinic, the use of iPSCs as a genetic disease model for pharmaceutical in vitro comparative studies is rapidly increasing. Whether the purpose is for manufacturing advanced cell and gene therapies, or for regenerative medicine, the potential for iPSCs to serve as a dependable platform is contingent on maintaining a scalable, defined, and stable iPSC culture.
The importance of maintaining a reliable and consistent iPSC culture
iPSCs should be evaluated regularly for four main qualities: morphology, genomic integrity, pluripotency, and differentiation potential. Together, these qualities define the “stemness” of the iPSC. Without this, the entire potential of the system fails because changes to any of these characteristics may present as confounding variables in vitro, or pose serious safety concerns in therapeutic applications.
Morphology can be a leading factor for iPSC culture health, and it can be monitored easily through daily examination with a basic light microscope. Stem cells should form tightly packed colonies with well-defined edges when grown in adherent flasks, or 3D spheroids when grown in suspension. Deviation from either morphology is a cause for concern and reason for further evaluation. Growth rate should also be considered when monitoring morphology, as an increase may indicate genomic instabilities that have conferred a growth advantage.
Genomic integrity refers to both mutations at the chromosomal level and within the genome. While some karyotypic abnormalities commonly acquired in iPSC culture may cause doubling times to decrease, not all will have an obvious effect on cell health. Karyotype abnormalities or spontaneous mutations in tumor suppressor genes can occur frequently in culture and raise safety concerns over using this cell type in therapeutic applications.
Pluripotency and differentiation potential are often thought to go hand-in-hand, but robust expression of the hallmark pluripotency markers, transcription factors Oct4 and Nanog, does not guarantee that the iPSC culture will be able to differentiate into all other cell types. High-throughput pluripotency assays can be used on a semi-regular basis to monitor culture health but should also be supported by regular confirmation of tri-lineage differentiation potential into the primary germ layers.
Using gene editing technologies to progress therapeutic iPSCs
Gene editing technologies and iPSCs have propelled the field forward by facilitating the development of isogenic genetic disease models and wild type controls, often made within a patient’s specific genomic context. Generation of these models still takes time and requires careful characterization of gene-edited clonal cell lines, which are often found only after screening hundreds of potential candidate clones.
The next frontier of personalized medicine is the autologous transplantation of genetically corrected iPSC-derived cells, with the potential to treat patients. Reaching this goal will require improvements to the efficiency and precision of gene editing technologies, as well as improvements to the speed and scale of clonal cell line generation and stem cell quality control.