Ongoing research at the University of Washington promises new methods for identifying and cataloging large numbers of cells quickly, which could lead to more individualized treatments in support of precision medicine initiatives
Researchers have found a new method for identifying specific cell types by groups, a breakthrough that some experts say could lead to new and more accurate methods for diagnosing and treating disease in individual patients, and new tools for fighting cancer and other chronic diseases. If this happens, both clinical laboratories and anatomic pathology labs would benefit from this technology.
A study published in the journal Science titled, “Comprehensive Single-Cell Transcriptional Profiling of a Multicellular Organism,” describes advances in cataloging cells that are much faster than the traditional method of using a microscope. The research is still in the experimental stage, but it is being hailed as both exciting and promising by experts in the field.
Barcoding Large Numbers of Cells for Viewing Simultaneously
To test their method, researchers from the University of Washington (UW) sequenced each cell of an individual Caenorhabditis elegans (nematode). Nematodes are transparent roundworms that have been extensively studied making them ideal for the UW study, since much information exists about their cellular structure.
The researchers developed a strategy they dubbed “single-cell combinatorial indexing RNA sequencing,” or “sci-RNA-seq” for short, to profile the transcriptomes of nuclei. A New York Times article on the study describes sci-RNA-seq as a kind of barcoding that shows which genes are active in each cell.
“We came up with this scheme that allows us to look at very large numbers of cells at the same time, without ever isolating a single cell,” noted Jay Shendure, PhD, MD, Professor of Genome Sciences at the University of Washington.
The UW researchers used sci-RNA-seq to measure the activity in 42,035 cells at the same time. Once all of the cells were tagged, or barcoded, the researchers broke them open so the sequences of tags could be read simultaneously.
“We defined consensus expression profiles for 27 cell types and recovered rare neuronal cell types corresponding to as few as one or two cells,” wrote the researchers in their published study.
Because such a rich body of research on nematodes exists, the researchers could easily compare the results that got to those procured in previous studies.
One Giant Leap for Medical Diagnostics
Identifying cell types has been a challenge to the medical community for at least 150 years. It is important for scientists to understand the most basic unity of life, but it has only been in the last few years that researchers have been able to measure transcriptomes in single cells. Even though the research so far is preliminary, the scientific community is excited about the results because—should the methods be refined—it could mean a great leap forward in the field of cell-typing.
However, the study did not identify all of the cell types known to exist in a nematode. “We don’t consider this a finished project,” stated Shendure in a New York Times article.
Nevertheless, researchers not associated with the study feel confident about the promise of the work. Cori Bargmann, PhD, a neurobiologist and Torsten N. Wiesel Professor at The Rockefeller University, and an Investigator for the Howard Hughes Medical Institute from 1995 to 2016, states that the results “will be valuable for me and for the whole field,” adding, “Of course, there’s more to do, but I am pretty optimistic that this can be solved.”
“The ability to measure the transcriptomes of single cells has only been feasible for a few years, and is becoming an extremely popular assay,” wrote Valentine Svensson, predoctoral fellow et al, of EMBL-EBI in the UK, in a paper titled, “Exponential Scaling of Single-Cell RNA-Seq in the Last Decade.” He added, “Technological developments and protocol improvements have fueled a consistent exponential increase in the numbers of cells studied in single cell RNA-seq analyses.” The UW research represents another such improvement.
Human Cell Atlas—Understanding the Basis of Life Itself
There are approximately 37-trillion cells in the human body and scientists have long believed there are 200 different cell types. Thus, there is an enormous difference between a nematode and a human body. For medical science to benefit from these studies, massive numbers of human cells must be identified and understood. Efforts are now underway to catalog and map them all.
The Human Cell Atlas (HCA) is an effort to catalog all of those disparate cell types. The mission of HCA is “To create comprehensive reference maps of all human cells—the fundamental units of life—as a basis for both understanding human health and diagnosing, monitoring, and treating disease.”
According to HCA’s website, having the atlas completed will impact our understanding of every aspect of human biology, from immunologic diseases to cancer. Aviv Regev, PhD, of the Broad Institute at MIT, who also is an Investigator with the HHMI and is co-chair of the organizing committee at the Human Cell Atlas notes, “The human cell atlas initiative will work through organs, tissues, and systems.”
One of the many complications of creating the atlas is that the locations of cells vary in humans. “The trick,” Regev noted in the New York Times article, “is to relate cells to the place they came from.” This would seem to be at the heart of the UW researchers’ new method for “barcoding” groups of cells.
Just as sequencing the entire human genome has brought about previously unimagined advances in science, so too will the research being conducted at the University of Washington, as well as the completion of the Human Cell Atlas Project. It is possible that pursuing the goal of quickly identifying and cataloging cells will lead to advances in anatomic pathology, and allow medical laboratory scientists to better interpret genetic variants, ultimately bringing healthcare closer to the delivery of true precision medicine.