Q&A: Could Cats Really Unlock A Long COVID Treatment?

StudyFinds’ Q&A With Dr. Amir Kol

What inspired you to study stem cell therapy in cats with FIP — and when did you first realize it could have relevance for human diseases like long COVID?

AK: Feline infectious peritonitis (FIP) has long been a tragic and untreatable disease in cats, driven by a feline coronavirus that causes intense systemic inflammation, T cell exhaustion, and progressive immune collapse. As a veterinary clinical pathologist and stem cell researcher, I was initially drawn to FIP because of its complexity and clinical relevance in companion animals. But it was the striking immunological parallels between FIP and severe human coronavirus syndromes — including long COVID and multisystem inflammatory syndrome in children (MIS-C) — that made it clear FIP could serve as a powerful translational model.

Our interest in mesenchymal stem/stromal cells (MSCs) as a therapeutic tool was strongly influenced by our earlier work in the simian immunodeficiency virus (SIV) model. In that study, we found that MSC therapy not only reduced inflammation but also restored germinal centers in gut-associated lymphoid tissue and enhanced antiviral immunity — outcomes that conventional antiretroviral therapy alone could not achieve. That experience taught us that MSCs could do more than suppress inflammation; they could help rebuild immune architecture and support long-term functional recovery.

Those lessons shaped the design of our FIP study. We asked whether MSCs could similarly promote lymphoid regeneration, reduce immune exhaustion, and support durable immune memory in the context of a natural coronavirus infection. The results exceeded our expectations. MSC therapy helped normalize lymphocyte counts, reduced expression of exhaustion markers, and shifted the immune landscape toward long-term memory formation.

It was through this combined lens — lessons from both SIV and FIP — that we recognized the broader relevance of our findings for human medicine. Studying naturally occurring diseases in animals not only advances veterinary care, but can also offer insights that inform innovative therapies for chronic viral illnesses in people.

Feline infectious peritonitis is a notoriously fatal disease. What were the biggest challenges in working with cats that were already so sick?

AK: Working with cats suffering from feline infectious peritonitis (FIP) was both scientifically challenging and emotionally demanding. FIP is a rapidly progressive and typically fatal disease, and by the time most cats are diagnosed, they are already critically ill. One of the biggest challenges was managing the advanced stage of disease in many of our patients — these cats presented with high fevers, effusions, severe systemic inflammation, and profound immune dysfunction.

From a clinical standpoint, this meant that timing was everything. Intervening early enough to give therapies like MSCs a chance to work — before irreversible organ damage set in — required careful coordination with referring veterinarians and dedicated owners. The cats needed supportive care, close monitoring, and frequent sampling, which required a highly collaborative and compassionate team approach.

Another major challenge was biological variability. Unlike lab models, these were outbred, immunocompetent animals living in real-world environments, with individual differences in genetics, viral load, immune status, and disease trajectory. While that variability made the study more complex to analyze, it also made it more meaningful — because it better reflects the clinical diversity seen in human patients with severe viral disease.

Perhaps the most powerful lesson was the resilience of these animals. Despite being so ill, many cats responded remarkably well to therapy. Seeing them recover — gaining weight, playing, and returning to their families — was incredibly rewarding and reinforced our belief in the translational potential of this work.

Your paper shows stem cells helped “reset” the immune system. Can you describe in plain terms what that looks like inside the body?

AK: When we say that MSCs helped “reset” the immune system, we mean they helped calm things down and get the body’s defenses working properly again.

In cats with FIP — and in people with illnesses like long COVID — the immune system gets stuck in overdrive. It’s like the body is hitting the gas pedal but never braking. This constant state of alarm wears out the immune cells, making them less effective, while inflammation causes more harm than good.

MSCs don’t fight the virus directly, but they act like peacekeepers. They travel to where the inflammation is worst and start releasing helpful signals. These signals tell the immune system to slow down, stop attacking healthy tissue, and start healing.

Inside the body, this looks like:

• Less inflammation, so tissues can start to recover.
• Tired immune cells get recharged, so they can do their job again.
• Immune “memory” starts to form, so the body can better recognize and fight the virus in the future.
• Healing signals increase, helping damaged areas repair themselves.

It’s a bit like turning off an alarm that’s been ringing too long — things quiet down, the immune system can reset, and the body gets a chance to heal properly. That’s what we saw in the treated cats, and it gives us hope for using this approach in people too.

Did any results from this study surprise you or go against your expectations?

AK: What stood out most to us was how consistent some of the treatment effects were, even under the challenging conditions of a small, variable study population.

We worked with just five cats per treatment group, and these were not controlled laboratory animals — they were community cats, each genetically unique and presenting at different stages of infection and disease progression. That kind of real-world variability typically makes it difficult to see clear patterns, especially when dealing with complex immune responses.

And yet, despite those limitations, we observed notable and biologically consistent effects in the MSC-treated group — including reduced T cell exhaustion, early signs of immune memory formation, and shifts in cytokine profiles that distinguished them from the antiviral-only group. These patterns emerged across multiple types of analysis, which added to our confidence in their biological relevance.

That said, we fully recognize that this was a small, exploratory study. While the findings are encouraging, they will need to be tested and validated in larger, more controlled cohorts to understand the full scope and consistency of MSC therapy’s effects. Still, the fact that we saw these signals in such a heterogeneous population suggests there may be a real and potentially broad-based benefit worth pursuing further.

You suggest that lingering inflammation in cats may mirror what happens in long COVID. Are there specific immune markers that made you draw that comparison?

AK: Yes — several immune markers supported that comparison. Even after treatment, some cats showed persistent elevation of inflammatory cytokines like IL-6 and IFNγ. This pattern of lingering inflammation and incomplete immune recovery closely parallels what’s been observed in people with long COVID.  

Stem cell therapy sometimes raises safety concerns. What did you learn about the risks — and how safe might this approach be for people?

AK: That’s a very important question, and one we took seriously. In our study, MSC therapy was well tolerated. The cats received intravenous MSCs and were closely monitored over 12 weeks. We saw no serious adverse effects, and clinical outcomes, including thrombosis, appetite, activity, and weight gain, generally improved in treated animals.

Of course, cats are not people, and any treatment would need to be carefully evaluated in human clinical trials. But our findings add to a growing body of evidence that MSCs can be safely administered — even in the setting of active viral infection — and may offer benefits without triggering harmful immune responses. It’s a promising step, but further safety studies are essential before moving forward in human patients.

What would the next steps look like if you were to test this therapy in humans or other species? Are clinical trials on the horizon?

AK: The next steps would focus on three key areas: confirming the results in larger studies, identifying which patients are most likely to benefit, and better understanding how MSCs work at the mechanistic level.

First, we need to repeat this study in a larger cohort of cats to validate the findings. A bigger sample size would allow us to control for more variables and assess how consistent the therapeutic effects really are across different stages of disease. It would also help clarify the durability of immune recovery over time.

Second, we’d want to begin identifying specific patient subsets — whether in animals or eventually in people — who respond best to MSC therapy. Not all patients with post-viral immune dysfunction are the same. Understanding which immune profiles predict a good response could help tailor treatment and avoid unnecessary interventions.

Third, although we’ve seen strong immunological signals, we still need deeper insight into how MSCs exert their effects — especially how they interact with exhausted T cells, promote immune memory, and potentially repair damaged lymphoid tissues.

While clinical trials in humans are not immediately on the horizon, this study strengthens the rationale for pursuing MSC therapy in conditions like long COVID or MIS-C. But before that happens, we must first do the work in well-controlled, species-relevant models to ensure both safety and efficacy.

Beyond COVID, could these findings be relevant for other post-viral syndromes or chronic inflammatory conditions?

AK: Our findings in cats with FIP closely parallel what we previously observed in our simian immunodeficiency virus (SIV) model (Weber MG, Walters-Laird CJ, Kol A et al, “Gut germinal center regeneration and enhanced antiviral immunity by mesenchymal stem/stromal cells in SIV infection,” JCI Insight) In that study, MSC therapy helped restore damaged lymphoid tissue and regenerate gut germinal centers — areas essential for mounting and maintaining effective immune responses. These effects were seen even in the presence of ongoing viral infection, suggesting that MSCs can support immune recovery even when the underlying trigger isn’t fully eliminated.

Taken together, the results from both models point to a broader potential for MSC therapy in treating post-viral syndromes and chronic inflammatory conditions where the immune system remains dysregulated long after the initial infection. 

The fact that we’ve now seen consistent patterns of immune restoration in two very different animal models — one retroviral, one coronavirus — reinforces the idea that MSCs may help reestablish immune balance in a wide range of chronic conditions, not just COVID-related ones.