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Adding a pivotal piece to the human development puzzle

By Matthew Pariselli  •  Sep 12, 2017

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SRI scientist uncovers significance of HEB gene

Raising a glass of champagne with her team members is how Dr. Michele Anderson, a senior scientist in Biological Sciences at Sunnybrook Research Institute (SRI), says she celebrates success. Considering the banner year she is enjoying, she should prepare for a few festive toasts.

Anderson has made a major discovery in the field of immunology. With colleagues, she has revealed the necessity of a transcription factor known as HEB in the early developmental processes of humans. Transcription factors are important molecules, so-called because they “transcribe” DNA into RNA, which is required to allow the functions of specific cell types. It’s a monumental finding that Anderson presents in the September issue of the highly regarded Stem Cell Reports journal, the online version of which is available.

Until now, the significance of HEB has only been known in mice; its importance in human biology has remained uncertain. It was this gap in knowledge that prompted Anderson, associate professor in the department of immunology at the University of Toronto, to collaborate with fellow SRI senior scientist Dr. Juan Carlos Zúñiga-Pflücker, chair of and professor in the department of immunology at U of T, to investigate its influence.

To do this, Anderson and her colleagues—who also include Peking University’s Dr. Yang Li and SRI research associate Dr. Patrick Brauer—conducted a series of experiments whereby they placed human embryonic stem cells in a Petri dish and instructed them to become T cells. Produced in the thymus, T cells are white blood cells that play a vital role in the immune system. Before inducing development, Anderson and her team used an innovative gene-editing technique called CRISPR-Cas9 to remove HEB. Knocking it out enabled them to assess its role in development—and the results were tremendously telling.

“What we found was that a lack of HEB has a profound impact on much, much earlier developmental processes in humans than we expected based on mouse studies,” Anderson says. “From the very early stages of human development, there was a partial block in the formation of a tissue type known as mesoderm, and in the ability to make tissues that arise from mesoderm, such as blood and heart muscle cells, without HEB.”

For the cells that made it through the block at the mesodermal stage, Anderson and her partners found that there was an additional hindrance at the point where they were meant to develop into hematopoietic cells. Furthermore, the surviving cells could not be directed to become T cells.

Anderson and her colleagues validated their results by placing the HEB gene back into the stem cells and noting that most of the defects were corrected. She calls this process “an in vitro form of gene therapy” that provides a proof of principle for therapeutic applications.

Anderson says the discovery contributes to “a new basic understanding of human developmental processes, and that has a profound impact in knowing what to look for in human diseases.” She says it’s imperative to establish knowledge of the human system to be able to tend to it in illness. “You can’t fix something if you don’t understand how it works to begin with.”

She adds, “What we’re really trying to understand is how these tissues develop normally, so when we take out a piece [HEB] and we see that it’s a problem, we know it’s an important piece.” Anderson notes that future steps include analyzing human diseases that involve mesodermal tissues and discerning whether the problems are connected to the HEB gene.

The potential clinical implications of her findings are exciting. Armed with the understanding that HEB is critical to the healthy development of T cells, Anderson says the goal now is to manufacture T cells for people who have lost them owing to HIV, radiotherapy or bone marrow transplant, for example. This is possible via the production of induced pluripotent stem cells, which are cells that have been cultivated and manipulated for particular therapeutic purposes. To make these, skin cells are taken and reprogrammed to become embryonic stem cells. Next, the embryonic stem cells are put through differentiation processes to create T cells, which ultimately could be given to people who need them for immunotherapy.

Anderson, who inherited the research gene from her scientist father, plans to have a hand in bringing the possible clinical impacts to fruition. She earned a one-year New Opportunities grant from Medicine by Design—which is a U of T program supported by the Canada First Research Excellence Fund—worth $50,000. She and Zúñiga-Pflücker will use the grant to engineer T cells more efficiently. If preliminary results are achieved, then they will look for further funding to continue the project.

It may be tough to believe, but unlocking the importance of HEB, having her article accepted into a prestigious journal and receiving a Medicine by Design grant are not the only accomplishments Anderson has added to her CV this year. In May, she was awarded a Project Grant from the Canadian Institutes of Health Research (CIHR). The approved proposal is to study the transcriptional regulation of gamma delta T cell development and functional diversification. She will receive $860,625 over five years. Moreover, Anderson’s application earned the highest final rating of the SRI submissions.

Addressing her reaction to the CIHR grant, Anderson laughs as she recalls initially thinking it was a mistake, as it was known to be an extremely tough competition. Once she learned that no error had been made and she was in fact a recipient, she says she felt validated and excited for the opportunity to do the proposed work. She adds that cutbacks in funding have made the work of scientists very difficult, but the security of five years’ worth of financial support is a great relief.

Provided with the means to pursue her passion, Anderson’s eyes are fixed on the future, and although she acknowledges the value of translational research, it’s the need for basic research that she stresses. “I’m very excited about the opportunities that I’ve been given. These are basic biology grants, and I think support of basic science is incredibly important,” she says. Having added one more piece to the puzzle, she’s keen to continue. “My primary goal is to understand how things work. That’s what drives me—that’s what I get the thrill of discovery from.”

In addition to CIHR, this research was supported by the Krembil Foundation and the National Institutes of Health.


In a nutshell

  • Scientists at Sunnybrook Research Institute have found that the HEB gene is essential in the early developmental processes of humans.
  • They used the gene-editing technique CRISPR-Cas9 to knock out HEB and evaluate its importance.
  • Their discovery will have an impact on the understanding of certain human diseases.