“The SPARK award helped me to gain valuable insights into these cells and set me on my path of academic independence. Exciting work lies ahead.”
Predicting patient responses to cancer immunotherapy
FUNDED: FEBRUARY 2018
FUNDED BY: The generosity of San Diego Advisor of the Year Awards Program
What was the goal of your SPARK project?
The immune system plays a pivotal role in the progression of atherosclerosis, the underlying cause of fatal cardiovascular events, including myocardial infarction and stroke. In previous work, I analyzed the immune cell landscape in aortas of atherosclerotic mice at different stages of disease. During the analysis of these data sets I identified a new aortic immune cell population, which appears to consist of T cell progenitors. T cell progenitors, so called thymocytes (CD4CD8 cells), are thought to only reside in the thymus. Finding them in the aorta may indicate that the thymus, where T cells develop, might have a leak allowing progenitors to escape. This could be potentially dangerous, as uncontrolled T cells responses can lead to autoimmunity. The SPARK award was used to further characterize and describe these new aortic immune cells.
SPARK project results:
I first screened 16 organs of non-atherosclerotic mice and was able to confirm the presence of CD4CD8 cells not only in the thymus as expected, but also the mediastinal fat and the aortic arch. Using state-of-the-art 3D whole mount fluorescence microcopy of tissue blocks containing the thymus, mediastinal fat, and the aortic arch I confirmed the presence of these cells in all three tissues. Interestingly, CD4CD8 cells in the arch were localized in clusters, whereas fat CD4CD8 cells were aligning along the vasculature in fat tissue. This points to an organization of these cells and argues against a random distribution. A significant amount of the SPARK award was used to gain further insight into the functionality and identity of these cells. To do so, I isolated CD4CD8 cells from the thymus, mediastinal fat, and aortic arch by flow cytometry and subjected those cells to an extremely low input sequencing protocol to assess their transcriptome. I could demonstrate that CD4CD8 cells isolated from the mediastinal fat and aortic arch could develop into functional T cells in a tissue culture experiment. However, in exploring their gene expression landscape, I found that extra-thymic CD4CD8 cells seem to be impaired in forming particular T cell responses. Further transcriptomic analysis revealed that extra-thymic CD4CD8 cells express factors, which are important for the maintenance of neurons. A functional innervation of the vasculature, among others, is essential to sense, integrate, and regulate blood pressure. Dysregulated blood pressure can lead to heart disease. Extra-thymic CD4CD8 cells might thus nurse nerves in vessels, a hypothesis I will test in future experiments.
What’s next for this project?
The SPARK award was instrumental in obtaining preliminary data regarding the presence and function of extra-thymic CD4CD8 cells. Based on these findings, I will soon write a manuscript describing for the first time the presence of CD4CD8 cells outside of the thymus. Future experiments will address how CD4CD8 cells leave the thymus to accumulate in mediastinal fat and the aortic arch, whether these cells occur in humans, how they survive in the extra-thymic environment and what their precise function in vivo is.
What’s next for Holger?
Beginning in 2020, I will start my own group as a W2/Assistant Professor in the Cardiology Department of the Medical Faculty at the University of Cologne. The findings and data from this SPARK project will be the basis for an independent research grant proposal that I plan to submit to the German Research Council (DFG). With the follow-up grant I would like to study the functionality and escape mechanisms of these cells in my own research group.