Technical challenges in using human induced pluripotent stem cells to model disease

Abstract

Reprogramming of human somatic cells uses readily accessible tissue, such as skin or blood, to generate embryonic-like induced pluripotent stem cells (iPSCs). This procedure has been applied to somatic cells from patients who are classified into a disease group, thus creating "disease-specific" iPSCs. Here, we examine the challenges and assumptions in creating a disease model from a single cell of the patient. Both the kinetics of disease onset and progression as well as the spatial localization of disease in the patient's body are challenges to disease modeling. New tools in genetic modification, reprogramming, biomaterials, and animal models can be used for addressing these challenges.

Figure 1. Technical challenges in generating cellular models of disease

Recapitulating disease in the laboratory requires reconstruction of both the kinetics of disease development and pathology (a) as well as in the interaction of the principal diseased cell type with other cell types in the patient’s body (b). In (a), the dynamics of disease progression in the patient is likely to take years, while phenotypes developing in vitro in cells differentiated from patient-specific hiPSCs could be achieved in days to months. This acceleration could be achieved through in vitro stress, including exposure of the cells to environmental effects such as oxidative stress, or by promoting “ageing” in vitro. In (b), cells are typically harvested from a patient through a blood sample or biopsy (shown in this example, although any part of the body could be used). The harvested sample is reprogrammed to generate hiPSCs, and a hiPSC line is subsequently differentiated to produce specific cell types thought to be affected by the disease. Interaction of the principal diseased cell type with other cell types within a tissue or within the diseased patient’s body may need to be reconstructed in vitro for effective disease modeling.

Figure 2. Emerging tools that may be used in disease modeling efforts

Four emerging tools may address technical challenges in modeling diseases in patients using hiPSC technology. On the far left is a schematic of the current approach to disease modeling through reprogramming. New reprogramming strategies utilizing gene excision, DNA transfection, protein transfection, and small molecules could generate hiPSCs without integrated factors in the genome, termed “factor-free” hiPSCs. Advances in genetic modification allow for the tracking, accentuating, or accelerating pathological phenotypes through introduction of cell type–specific lineage reporters, as well as disruption, repair or overexpression of specific genes (e.g., GFP or disease-gene-of-interest, “disease-GOI”). Biomaterials can provide tailored microenvironmental stimuli, which include neighboring cells, extracellular matrix, soluble factors and physical forces, in order to reveal pathological mechanisms. Human-animal chimeras with human blood, neurons, and other tissues have been generated, and these tools could be used to interrogate the in vivo function of hiPSC derivatives.