Tom Riffelmacher, Ph.D.

A new cellular target to prevent tissue damage following heart attack

FUNDED BY: the generosity of The Rickey Family

What was the goal of your SPARK project?

I was always fascinated with the question of how the lack of oxygen would impact immune functions on a cellular level. Of course, it didn’t take a pandemic to teach us how quickly we are in trouble when we can´t breathe — but what does the lack of oxygen mean to our immune cells within tissue? During a heart attack, a stroke and in sickle cell disease, blood vessels become clogged, but we don’t understand, on a cellular level, the impact this hypoxia has on the inflammatory response that follows. Using single cell RNA sequencing, I sought to explore the mechanistic changes within innate immune cells in this context, to see if it offers cues to novel druggable targets.

Pivoting during a pandemic

The pandemic presented significant challenges to my project because my original plan relied on outpatient samples from patients who suffered heart attacks. Unfortunately, these samples were no longer collected during the pandemic. Also, since my original collaborator was in the U.K. and I was going to have to travel to retrieve the samples, that wasn’t possible due to the travel bans between the U.S. and Europe. So I had to step back and think about what I could do, in the short time frame I had, to address this question with what is available more locally. Fortunately, thanks to a previous clinical study collaboration between LJI and the University of Wisconsin, I was able to get access to blood samples from sickle cell disease patients. This is a disease of chronic, recurring episodes of blood vessel occlusion, which causes inflammation of the lung. Simultaneously, I used a mouse model of sickle cell disease, harbouring the human disease-causing mutation in the haemoglobin gene, for mechanistic follow-up experiments. With these samples, I was still able to explore the impact of vaso-occlusion and resulting hypoxia on immune cells, albeit in a different disease context.

SPARK project results:

I initially set up a single cell sorting strategy to isolate the Natural Killer T (“NKT”) cells and optimize the conditions using the phlebotomy core at LJI for sourcing blood (once it reopened). We requested and received IRB approval to get healthy African American volunteers to donate blood at LJI as appropriate controls for sickle cell patients. I then sorted the relevant immune cells from over 20 sickle cell disease patients and controls. Originally, I proposed to focus only on NKT cells, but we realized, thanks to the capabilities of LJI’s sequencing and bioinformatics teams, that we could add four more relevant innate lymphocyte populations. I am now analyzing the data from a total of 10,841 lymphocytes to test if we find evidence for altered inflammatory signaling. The first results were promising, indicating that innate lymphocytes were noticeably depleted in the blood of patients but not in the controls, meaning they may have been recruited into the lung tissue to mediate inflammation. There were several thousand genes differentially expressed, including the pathways that produce inflammatory cytokines. Having the humanized mouse model allowed me to study this in more detail within lung tissue, which of course we cannot get from patients. Indeed, inside the lungs, the NKT cells dramatically increased in numbers and contributed to inflammation. They were also metabolically different. Due to the logistical challenges and need to really pivot my project, I have an extension to finish this through December 2021, so some of my results are still pending additional experiments and analysis.

What’s next for this project?

Thanks to the huge dataset I was able to obtain with the help of the SPARK award, I have a powerful tool that will help to understand the mechanism of how inflammation is mediated in response to the vaso-occlusive crisis. The data have already pointed us to relevant mediators of inflammation, which I am now following up on with mechanistic experiments. We would like to fully understand the mechanisms underlying this, and relate it to how it compares to inflammation following heart attacks – which we will be able to do using the patient sample data. While we may still be adding more data to this during the extension period, this represents a solid foundation that will facilitate future research into this area.

What’s next for Tom?

With the goal of becoming an independent investigator in mind, I have applied for a National Institutes of Health (NIH) K99 grant, which provides funding to promising young investigators to help them transition into faculty positions. I am also applying to similar grants in Germany, which is where I am originally from. So my hope is that I will be able to make this transition in the next couple of years in either the U.S. or Germany. Regardless of where I obtain a position, I remain interested in this line of immunology research and hope to continue this work in the future.