This blog is part of the Month of CIRM series and the first of two blogs focused on how CIRM-funded infrastructure initiatives are developing useful tools to advance stem cell research.
Human stem cells are powerful tools for studying human disease. Animal models like mice have been and continue to be important for studying physiological systems, but they are still different than human systems. Other types of human cells studied in the lab often are isolated from cancers or modified to multiply indefinitely. However, the genetic DNA blueprint of these modified cells are irreparably altered from the normal tissues that they came from.
Human pluripotent stem cells are unique in that they can be grown in the lab and turned into any type of normal cell in the body. Many scientists now believe that creating such stem cell lines from patients and developing ‘disease-in-a-dish’ models will provide important insights that will lead to treatments for the disorders from which they came. Challenges still remain to develop these models to their fullest potential. Because the genetics underlying human disease is complex, detailed genetic information about each stem cell line, as well as a large number of lines to represent the genetic variability between patients will be needed to make progress.
To address this need, CIRM funded the creation of the world’s largest induced pluripotent stem cell bank, which we call the CIRM iPSC Repository. iPSCs are similar to embryonic stem cells in that they can develop into any cell type found in the body, but they differ in how they are derived. Scientists can take human skin or blood cells and genetically reprogram them into iPSCs that have the same genetic makeup, including any disease-causing mutations, as the person from which the original cells were taken. Embryonic stem cells, on the other hand, are derived from left over embryos donated by couples undergoing in vitro fertilization (IVF) treatments.
The CIRM iPSC Repository was established to harness the power of iPSCs as tools for disease modeling and drug discovery. The Repository currently offers scientists around the world access to over 1500 high-quality iPSC lines covering diseases of the brain, heart, liver, lung, and eye, and the collection will eventually hold over 3000 lines. All iPSC lines are linked to publicly-accessible demographic and clinical information.
Making the Cell Lines
Making the iPSC Repository was no easy task – it took a village of doctors, scientists, patients and healthy volunteers. First, clinicians across California collected blood and skin samples from over 2800 people including individuals with common diseases, rare diseases and healthy controls. CIRM then awarded a grant to Cellular Dynamics International to create iPSC lines from these donors, and a second grant to the Coriell Institute to store and distribute the lines to interested labs around the world. Creating such a large number of lines in a single concerted effort has been a challenging logistical feat that has taken almost five years and is projected to finish in early 2018.
We spoke with one of the tissue collectors, a scientist named Dr. Joachim Hallmayer at Stanford University, about the effort it took to obtain tissue samples for the Repository. Hallmayer is a Professor of Psychiatry and Behavioral Sciences at Stanford who studies Autism Spectrum Disorder (ASD) in children. With funding from a CIRM Tissue Collection for Disease Modeling award, Hallmayer collected tissue samples from children with ASD and children with normal development. His efforts resulted in the 164 ASD and 134 control samples for the Repository.
Hallmayer emphasized that each sample donation required significant attention and education from the clinical staff to the donor. Communicating with patients and walking them through the consent process for donating their tissue for this purpose is an extremely important issue that is often overlooked. “Conveying information about the tissue collection process to patients takes a lot of time. However, deconstructing the consent process is essential for patients to understand what they are donating and why,” explained Hallmayer.
Now that the ASD lines are available, Hallmayer and his colleague Dr. Ruth O’Hara are formulating a plan to model ASD in a dish by differentiating the iPSC lines into neurons affected by this disorder. Says O’Hara:
“While the examination of live tissue from other organ systems has become increasingly viable, examining live neurons from patients with brain disorders has simply not been possible. Using iPSC-derived neurons, for the first time we can study live nerve cells from actual patients and compare these cells to those from humans without the disorder.”
Using iPSCs to Model Psychiatric Disorders
Ultimately, the goal of iPSCs for modeling disease is to identify mechanisms and therapeutic targets for the disorders that they represent. Studying a disease through a single iPSC line may not shed enough light on that disorder. Just as people have diverse traits, the way that a disease can affect individuals is also diverse. Studying large numbers of lines in a time and cost-efficient manner that represent these diverse traits, and the genetic causes that underlie them, can be a powerful method to understand and address diseases.
To leverage the iPSC collection for this purpose, CIRM and a group of scientists at the Broad Institute’s Stanley Center for Psychiatric Research and Harvard University have entered into a collaboration to study psychiatric disorders such as ASD. Because the donor samples were collected on the basis of clinical information, the genetic information about what caused their disease remains unknown. Therefore, the Stanley Center will embark on whole genome sequencing (WGS) of hundreds of lines from the CIRM iPSC repository. Adding donor WGS sequence information to the CIRM repository will significantly increase its value, as scientists will be able to use DNA sequence information to select the ideal lines for disease modeling and therapeutic discovery efforts. The collaboration aims to identify the genes that shape neuronal phenotypes in iPSC-derived neurons from patients with psychiatric disorders.
“A central challenge today is to discover how inherited genetic variation gives rise to functional variation in the properties of neurons and other cells,” said Steven McCarroll, Director of Genetics at the Broad Institute’s Stanley Center for Psychiatric Research, and associate professor at Harvard Medical School’s Department of Genetics. “We hope with the analysis of cells from very large numbers of genetically diverse individuals will begin to address longstanding problems at the interface of human genetics and biology.”
iPSC derived neurons growing in a dish. (Image courtesy of Ralda Nehme, Research Scientist at the Broad Institute).
Such efforts require technologies such as Drop-seq, developed in the McCarroll lab, where genome-wide expression of thousands of separate cells can be analyzed in one experiment. These efforts also rely on scaling functional analysis of stem cell-based disease models, a vexing bottleneck for the field. “The CIRM iPSC Repository is the largest and most ambitious of its kind”, said Kevin Eggan, Professor of Stem Cell and Regenerative Biology at Harvard University, and Director of Stem Cell Biology at the Broad Institute’s Stanley Center for Psychiatric Research. Efforts underway in Dr. Eggan’s lab are directed at developing approaches to analyze large numbers of stem cell lines in parallel.
“The scale of the CIRM iPSC collection will allow us to investigate how variation that is common among many of us predisposes certain individuals to major mental illnesses such as autism and other neurodevelopmental disorders. We are incredibly excited about entering this long-term collaboration.”
Members of the Eggan and McCarroll labs at the Broad Institute’s Stanley Center for Psychiatric Research. (Image courtesy of Kiki Lilliehook)
From Cell Lines to Data
It’s clear from these stories, that the iPSC Repository is a unique and powerful tool for the stem cell research community. But for the rewards to be truly reaped, more tools are needed that will help scientists study these cell lines. This is where the CIRM Genomics Initiative comes into play.
Be sure to read Part 2 of our Stem Cell Tools series tomorrow to find out how our Genomics Initiative is funding the development of genomic and bioinformatics tools that will allow scientists to decipher complex stem cell data all the way from mapping the developmental states of cells to predicting the accuracy of stem cell-based models.
This blog was written in collaboration with Dr. Kiki Lilliehook, the Manager of the Stem Cell Program at the Stanley Center for Psychiatric Research at the Broad Institute in Cambridge, Massachusetts.