Julie Burel, Ph.D.

Immune crosstalk may improve the diagnosis of infectious diseases


FUNDED BY: The generosity of LJI Board Director Larry Spitcaufsky and Tiki Spitcaufsky.

What was the goal of your SPARK project?

There are many types of immune cells, and we’re still figuring out how they work together. One interesting immune cell pairing is T cell: monocyte “doublets.” For years, scientists have been seeing these conjoined cell pairs in patient samples, but many regarded doublets as an accidental artifact of the flow cytometry process, and it was common place to “dump” those conjoined cells before gathering data. We wondered—could doublets actually be a sign that the immune system is fighting off a disease? To answer this question, we needed to overcome the technological hurdles that make it difficult to detect doublets in patient samples. We also needed to isolate their genetic signatures to learn more about what they’re doing in the body.

SPARK project results:

My project showed that combining several cell imaging techniques allows us to visualize, for the first time, immune cell doublets in human peripheral blood. We focused on a particular type of cell doublets, pairing one patrolling cell (myeloid lineage, monocyte) and one fighting cell (lymphocyte lineage, T cell). We looked at how common these doublets were and how they were functioning in healthy individuals, as well as, in the context of infection and vaccination. We found that doublet frequency fluctuates over time following tuberculosis treatment or Tdap vaccination. Doublet levels are also higher in patients with severe cases of dengue fever. With the publication of this research in eLife in June 2020, our group is now positioned as a major contributor in this completely novel field of research. At the same time, I addressed several technological challenges in the field. This work, published in the journal Cytometry Part A in May 2020, revealed that current single-cell technologies are not sensitive enough to reliably flag the presence of doublets within human cell suspensions such as human blood, which will “contaminate” single-cell studies and potentially lead to wrong interpretations, such as the discovery of novel immune cell types with mixed lineage features. To help address this technology gap, I identified robust data analysis and experimental strategies to help other researchers distinguish between doublets and singlets, and thus avoid data misinterpretation. Finally, I launched an experiment to use RNA sequencing to study which types of T cells and monocytes tend to be present in doublets. This work may open the door to understanding doublet biology.

What’s next for this project?

After seeing the results from the experiments funded by my SPARK award, my Principal Investigator, Bjoern Peters, Ph.D.committed some additional funding to further this study this past spring. This allowed me to perform single-cell RNA sequencing data in T cells and monocytes in doublets vs. singlets isolated from a small number of patients with active tuberculosis. My hope is that this small dataset will shed light on many outstanding questions about how doublets form, and which information they contain.
Analysis of this pilot dataset showed that T cells pairing with a monocyte are enriched for antigen-specific signaling gene signatures, suggesting they might represent a critical cell population for better characterizing T cell immune responses in humans. I’ve used these results as preliminary data to apply for an R21 grant from the National Institutes of Health (NIH) this summer, which if I win, would provide $500,000 to continue this work over the next two years. I should hear back on my application this upcoming winter or spring. An important part of my work now is to share the existence and importance of doublets with the scientific community. Scientists need the resources and expertise to distinguish doublets from single cells. In this vein, I was invited to give an international webinar in April 2020 on the use of imaging flow cytometry to help detect doublets in “suspicious” dual-expressing cell populations.

What’s next for Julie?

In January 2020, I was promoted to Instructor at LJI. In this new position, I’m aiming to gain more independence in my research by securing funding for projects I’d like to pursue, as I’ve had the opportunity to do so through the Tullie and Rickey Families SPARK Awards program. My hope is to return to Europe and start my own research group there in a few years, focusing on better understanding immunity to infectious diseases using systems biology approaches. A key question that fascinates me is how diverse the human population is in terms of immune responses, and how it shapes infection and vaccination outcomes globally.