Research Applications for Engineered iPS Cells

This new understanding of pathologies opens the door to new treatment options, prior to the irreversible onset of disease.

Modeling diseases with iPSC has been a driving force in the development of many new or improved technologies but has also strongly benefited from the advances in genome sequencing and engineering tools. This combination has brought hope to patients who had little. Rare diseases often remained unstudied since the investment into creating cell models and study them was seen as too high versus the profit that could be generated. Or we simply did not have the ability to create complex cellular models that could be used. Today, by combining iPS technology with whole genome sequencing, mutations can be easily identified. We can then make use of technologies like CRISPR/Cas9 and create iPS lines where the mutation can be introduced or corrected. The direct link between genotype and phenotype can be made in a fairly efficient and quick way. One example where these advances have been highly beneficial is retinal studies. The retina is composed of multiple highly specialized interconnected cell types, such as the RPE (retinal pigment epithelium) and PR (photoreceptors). These are terminally differentiated cells prone to ageing related degeneration and to mutational impact. While in the past we were unable to mimic such a high level of complexity, we can now generate RPE and even mini retinas that allow us to understand tissue development, pathways and impact of mutations.

Another highly relevant application of iPS cells is in drug development and screening. With iPSC we have gained deeper understanding of the molecular pathways involved in a disease, found new phenotypes, and are now also able to generate relevant cellular models, in enough number, to perform high throughput screening (HTS) with easy read outs, such as luciferase or GFP expression. For example, iPS derived motor neurons from ALS patients allowed the screening of a large library of compounds able to suppress neuron cell death and identified a drug already in use for the treatment of chronic myelogenous leukemia, bosutinib (3). We can even look back at current treatment options and try to understand their real benefit in light of our newly acquired knowledge of the disease. This is the case in schizophrenia, where iPSC derived from schizophrenic patients have shown lower levels of PSD95 (postsynaptic density protein-95), glutamate receptor, and decreased axon number. Testing of five commonly used antipsychotic drugs indicated that only one had a real effect in increasing neural connectivity.

In addition to drug development, toxicity and cell permeability studies can now also be conducted in relevant cell systems. The ability to test toxicity profiles of drug candidates in cell types that can mimic more closely the actual target tissue, and even its complexity, can increase the predictability of drug behavior in humans. A better understanding of the toxicology profile of a candidate drug can benefit the patients by identifying drugs that can act with fewer severe side effects, while avoiding large and expensive dose escalation studies.

Initial studies had focused on the generation of autologous cell therapies, where the patient’s cells would be reprogrammed, genetic mutations would be corrected (if applicable), differentiated into the cell type needed and reintroduced into the patient. While this is still possible in certain cases, it has become clear that the timeframe involved is not compatible with the progression of some diseases. Attention has been shifting to the use of allogeneic alternatives, and the creation of ‘off-the-shelf” therapies. The use of allogeneic cells brings its own concerns, such as the potential for immune rejection due to the mismatch of HLAs (human leukocyte antigens) between donor and recipient. Countries like Japan are attempting to create a bank of iPS cells that covers 95% of the Japanese population, a major undertaking that will require more than 140 different cell lines. Other strategies involve the creation of universal donor lines, where B2M (beta 2 microglobulin) and CIITA (class II major histocompatibility complex transactivator) are not present and thus do not express class I and II HLA on the cell surface. Clinical trials based on iPS derived cells are underway in the US, China, Germany, and Japan, targeting a number of diseases (examples can be seen in Table 1) (1,3).

Table 1: Examples of diseases targeted in clinical trials using iPS derived cells, and cell types being used.

While bringing major advantages, certain aspects should be kept in mind. Interestingly, iPSCs tend to retain some epigenetic memory, which impacts their ability to differentiate (4), and should undergo strict quality control to determine the presence of tumorigenic cells in the final cell population, including the residual presence of iPSCs. Another aspect often neglected is the need to assess the cell maturity level, via specific markers and characteristics. The use of immature cells can result in detrimental consequences, as in the case of cell replacement with immature cardiomyocytes which generate arrhythmia.

The future is bright for iPS cell-based research and therapy. Fine tuning of aspects such as our ability to model late onset diseases in a short timeframe, develop vascularization and specific spatial-temporal differentiation control, will advance the field and allow better therapies. BPS Bioscience offers iPS cell lines expressing reporter genes, such as GFP and luciferase, that allow an easy readout in HTS drug screening and toxicity assays. In addition, we also provide Cas9 expressing iPS cells, a perfect tool for efficient genetic manipulation for your studies of disease in a dish or therapeutic applications, making us an ideal partner in your research endeavors.