During pollen season in North Carolina, relieving allergy symptoms with antihistamines can be top of mind for many of us, but what is below the surface causing the itchy eyes and scratchy throats are mast cells behaving badly.

Dr. Glenn Cruse, an associate professor of immunology at the NC State College of Veterinary Medicine, studies those reactionary cells, specifically how they drive inflammatory processes in asthma, atopic dermatitis and allergic diseases. His molecular biology lab at the college also studies mast cell proliferation diseases, such as mastocytosis and mast cell leukemia, which are rare but often devastating.

In his research, partly funded by the National Institutes of Health, Cruse looks at the molecular mechanisms — including genes and proteins — that control mast cell function, with the hope of developing ways to prevent mast cells from being activated. His research also aims to develop therapeutics for cancer by inhibiting the KIT growth factor receptor in mast cells. 

We talked with Cruse, named an NC State University Faculty Scholar in 2024, about his important work.

Q: How do you describe what your research is targeting?

DR. GLENN CRUSE: Mast cells are long-lived tissue cells that can also originate from bone marrow, where they circulate in the blood as immature progenitors that can be recruited to join sites of allergic inflammation. At this time of year, with all the tree pollen out there, we’re all getting sneezy and itchy eyes and even itchy skin. Mast cells release granules, which store histamine, and that is what we mostly target when we’re thinking about allergic inflammation. Histamine acts on the blood vessels and helps promote inflammation.

The mast cell itself binds to an immunoglobulin called IgE. IgE was probably derived to help us defend against parasites and parasitic infections, and then because we don’t really get much of those anymore, I guess it got kind of bored and decided to find something else to fight against. It now mostly is known for its fighting against allergens, which are otherwise innocuous things that will trigger your immune response. 

We understand what mast cells do. They get activated by allergens to trigger inflammation. What my lab is looking for are the underlying mechanisms of that activation. The main goal would be to try and find proteins that are specific to a mast cell — a protein or even just a pathway, because there are a couple of pathways in the signaling cascade that we’re not entirely sure how exactly they are working. We want to identify those novel potential targets that could be used to stop mast cells from inducing that initial inflammatory response. If we can do that, then we can hopefully identify better therapeutics that are more specific and more effective. One avenue we currently are pursuing are a family of proteins encoded by the MS4A gene family that have been associated with asthma susceptibility. 

Q: What would you consider your latest breakthrough?

CRUSE: In terms of the allergy component, one of our recent findings was to identify one of these MS4A proteins that had an unknown function. We have been looking at the IgE receptor, which drives the initiation of the inflammatory response. Almost nine years ago, we found that you can target a subunit of that receptor that binds the proteins to the IgE on the surface of the cell, and you don’t get the activation of the mast cell through those allergens. This subunit is called MS4A2.

We found that if you target the mRNA encoding MS4A2 with short, synthetic DNA or RNA sequences, a cell will take out pieces of the RNA and fuse other pieces together to make a variant form of the MS4A2 protein missing important sections. 

When a protein is encoded, the cell splices out all the introns in the code, but it could also splice out some exons [in genetics, exons are coding regions of DNA that are present in the final mRNA molecule and used to produce proteins, while introns are noncoding regions that are removed during RNA splicing]. We can target that and selectively pull out an exon that’s important in MS4A2 protein’s function. Then we were able to target that specific exon so that when MS4A2 is produced, it was missing just a little, but critical, piece.

By taking that little piece out, the MS4A2 subunit no longer interacted with the IgE receptor complex so we could actually completely stop the mast cells from getting activated by allergens. However, these studies were done in the mouse. One issue we found is that this targeting of MS4A2 doesn’t work as well in humans, suggesting that perhaps there were compensatory mechanisms in humans that were not present in mice. 

Q: What materials do you use to conduct your research?

CRUSE: We have a lot of different ways we do it. We work from the genetic level up to the whole animal. We start with doing things like molecular analysis and looking at gene expression in human cells and then using mice models to see whether what we come up with works. We’re primarily interested in asthma, because the role of mast cells in allergic asthma is pretty well-defined, and we know that they’re very important in the disease pathophysiology. We do a lot of signaling where we will stimulate lung mast cells and then look at what proteins are phosphorylated, or activated, within signaling pathways so that we can work out what pathways are affected by what proteins. We do a lot of that in vitro on human and mouse cells in the lab. 

Then we can obtain lung samples from our clinical collaborators at UNC and Rutgers University, to look at expression in the lungs of control patients or patients with asthma, and we see if the proteins are changing in expression within the non-diseased versus the diseased lung. We can also look at tissue samples from human lungs, treating them with certain compounds and seeing how the airways constrict and how they cause inflammation within that lung tissue. That’s as close as we can get to looking at how these pathways are functioning within the organ themselves in humans. We also employ mouse asthma models where possible, if we find that the mechanisms are conserved between species. 

Q: How close are you to finding a new therapeutic for asthma?

CRUSE: We’re getting a lot closer. In 2023, we found and published about a mechanism explaining why human cells were less affected when we targeted MS4A2 compared to mouse cells. We established that another related protein, MS4A6A, can kind of compensate for MS4A2 protein and started working with a pharmaceutical company, Hoth Therapeutics, to look at whether we can target both of these proteins therapeutically with the oligonucleotides [short, synthetic DNA or RNA sequences used in drug development]. The route to therapeutic development in that application is long, because asthma is a chronic disease where you would have to have a long-term treatment, and the underlying mechanisms are complex. Where we are closer is in the other aspect of what we do, which is cancer. 

We previously found an exon-skipping oligonucleotide, which we have termed KitStop, that safely reduces the severity and duration of the anaphylactic response by depopulating mast cells in tissues. We target a growth factor receptor called KIT that’s critical for mast cell survival and force it to produce a different version of that mRNA code for a protein. By doing that, we make the protein and growth factor receptor nonfunctional, essentially causing mast cells to die. 

This targeting technology holds promise for developing a new cancer treatment. Cancer of mast cells, such as mastocytosis, is rare, and in some severe versions you get mast cells basically invading all of your tissues. Systemic disease, with multiple organ involvement, becomes a very serious proliferative mast cell disorder. It can also develop into mast cell leukemia, where you start to see mast cells in the blood — which you should never see, because they’re tissue resident cells. There’s an unmet need for a therapeutic that can selectively kill mast cells, because they can become resistant a lot of the time to the inhibitors and therapeutics currently in use for mastocytosis.

Q: Could this process have applications in other cancers?

CRUSE: Potentially. We’re trying to finish a paper where we’re also looking at it in gastrointestinal stromal tumors [GIST], which are a tumor of the interstitial cells in the GI tract. These GIST cells express that same KIT protein, and most of the patients have an activating mutation in KIT protein as well. So much like mastocytosis, it also has an activating mutation in a growth factor receptor, and so we target that in those GI cells. We’ve shown that we can also markedly reduce the growth of that cancer in mouse models. 

There are potentially other cancers where the KIT protein may play a role in either growth and survival, or metastasis of cancer cells. Since it is a growth factor receptor and proto-oncogene [a normal gene that plays a role in regulating cell growth and division], it can be involved in other tumors as well. Mutations in that protein can make the cells transform into cancer cells in some cancers. 

Our therapeutic in the Hoth pipeline based on KitStop, called HT-KIT, works. It’s an oligonucleotide-based therapy, kind of like an RNA therapeutic that can stop the activating signal of certain tumor cells and certain cancer cells to divide and proliferate, and so it inhibits that cell division and actually kills those cancer cells. We’re currently doing things like safety studies, and we are working toward getting a drug into clinical trials in the not too far future.

Q: What was your path to NC State?

CRUSE: In 2016, I was part of the dean’s hires for the ‘allergy-itch’ cluster. I guess I was the ‘allergy’ one, and Dr. Santosh Mishra was the ‘itch’ one. Remarkably, we were both brought in from the same place, the NIH. 

Q: I can tell you love what you do.
CRUSE: Yes, absolutely. It’s never the same for too long. We end up going down pathways that you think are going to go in one direction, and they end up going in a completely different direction. And I think it’s that surprise that really helps to drive, to keep the interest alive. Nothing’s ever quite what you think it might be. In science, you have a hypothesis. If it is not true and it goes in a different direction, sometimes that’s more exciting than if it actually does what you predicted it to do.