In a Nutshell
- A UC Davis study tested stem cell therapy in cats with a deadly coronavirus to explore new treatments for immune dysfunction.
- Cats given stem cells plus antiviral drugs showed better recovery of healthy immune function compared to antivirals alone.
- Feline infectious peritonitis (FIP) closely mimics severe COVID-19 immune problems, making it a strong translational model.
- While results are promising, human trials are needed to confirm whether this approach could help people with severe COVID-19 or long COVID.
DAVIS, Calif. — A breakthrough study using cats with a deadly coronavirus infection suggests that stem cell therapy could offer a promising new approach for helping people recover from severe COVID-19 and long COVID symptoms. Researchers at UC Davis discovered that cats treated with mesenchymal stem cells alongside antiviral drugs showed enhanced immune recovery compared to those receiving antiviral treatment alone.
The research is particularly striking because feline infectious peritonitis (FIP) — the disease studied in cats — mirrors many of the same devastating immune problems seen in severe human coronavirus infections. Both conditions trigger what scientists call a “cytokine storm,” cause profound immune cell depletion, and leave patients with exhausted immune systems that struggle to mount effective responses.
“Severe coronavirus infections, including SARS-CoV-2, are marked by systemic inflammation, T-cell exhaustion, lymphopenia, and chronic immune dysfunction, with limited therapeutic options for recovery,” the researchers wrote in their study published in Stem Cells Translational Medicine.
How Stem Cell Therapy Actually Works
Researchers initially enrolled 11 cats naturally infected with FIP and divided them into two groups: five cats received the standard antiviral treatment (GS-441524, which is related to remdesivir used in COVID-19 patients), while five others received the same antiviral plus two doses of mesenchymal stem cells delivered intravenously two weeks apart. (One cat’s sample was later excluded due to outlier data.)
Scientists used advanced techniques to analyze what was happening inside the cats’ immune systems. They performed single-cell RNA sequencing on lymph node samples, measured dozens of inflammatory molecules in blood, and tracked immune cell populations over 12 weeks of treatment.
Mesenchymal stem cells can be harvested from a patient’s own fat tissue or from donors, expanded in the lab, and then infused back into patients. These cells have well-known anti-inflammatory properties and can help coordinate immune system repair.
The Recovery Results Were Promising
Cats that received stem cell therapy showed improved aspects of immune recovery across multiple measures. Their immune systems appeared to “reset” in ways that the antiviral-only group did not achieve. Most notably, the stem cell-treated cats showed reduced signs of T-cell exhaustion — a condition where the immune system’s killer cells become worn out and ineffective. In the stem cell group, genes associated with exhausted, dysfunctional immune cells were significantly reduced, while genes linked to healthy immune memory were increased. The stem cell therapy also helped the cats develop more regulatory T-cells, which act like peacekeepers that help maintain immune balance.
The stem cell treatment also helped normalize the cats’ inflammatory profiles. While both treatment groups showed improvement over time, the cats receiving stem cells maintained more balanced immune responses without the overactivation sometimes seen in the antiviral-only group.
Perhaps most encouraging, the stem cell treatment appeared to promote the development of long-term immune memory — the type of durable protection that helps prevent reinfection and provides lasting immunity.
Safety was a major concern, especially since previous research has raised questions about potential blood clot risks with stem cell treatments. However, the study found no severe adverse effects in any of the cats, even with high doses of stem cells.
Tackling Long-Term Viral Effects
One of the most intriguing aspects of the research relates to persistent inflammation after viral recovery. Even after the cats had undetectable viral loads for weeks, researchers found evidence of ongoing immune activation — similar to the chronic inflammation seen in long COVID patients.
The study revealed three distinct patterns of inflammatory molecules, with some cats transitioning toward healthier profiles over time while others remained in inflammatory states. Notably, a growth factor called PDGF-bb was uniquely associated with immune cell recovery, suggesting it could serve as a biomarker for healing.
“Notably, residual cytokine elevations persisted at the study’s end, mirroring features of chronic immune dysregulation,” the researchers noted, drawing direct parallels to long COVID syndrome.
What This Means for Long COVID Patients
The research provides a potential roadmap for treating the millions of people worldwide who continue to suffer from long COVID symptoms. Current treatments for long COVID are limited and largely supportive, leaving patients with few options for addressing persistent fatigue, brain fog, and other debilitating symptoms.
Stem cell therapy could, in the future, offer a way to actively repair the immune dysfunction that underlies many long COVID symptoms. The treatment appears to work by reducing harmful inflammation while simultaneously rebuilding healthy immune responses.
While this research is promising, human clinical trials will be needed to confirm whether stem cell therapy can provide similar benefits for COVID-19 and long COVID patients. The researchers acknowledge that their study was relatively small and didn’t include cats with the most severe illness, which limits how broadly the findings can be applied.
However, the detailed molecular analysis provided new insight into exactly how stem cell therapy helps repair viral-damaged immune systems. For the millions of people still struggling with the long-term effects of COVID-19, this research offers hope that effective treatments may be within reach. The key insight that immune dysfunction — not just inflammation — needs to be actively addressed could fundamentally change how doctors approach post-viral syndromes.
Disclaimer: This article summarizes early-stage preclinical research in animals. While the results suggest promising potential for human health, stem cell therapy for COVID-19 or long COVID is not yet an approved or proven treatment. Always consult a qualified healthcare professional before considering any medical intervention.
Paper Summary
Methodology
Researchers conducted a randomized controlled trial with 11 cats naturally infected with feline infectious peritonitis (FIP). Five cats received standard antiviral treatment (GS-441524) alone, while five received the same antiviral plus two intravenous doses of mesenchymal stem cells two weeks apart. The team collected blood, tissue fluid, and lymph node samples over 12 weeks, analyzing them using advanced techniques including single-cell RNA sequencing, flow cytometry, and multiplex cytokine analysis to track immune system changes.
Results
Cats receiving stem cell therapy showed enhanced aspects of immune recovery compared to those getting antiviral treatment alone. The stem cell group had reduced T-cell exhaustion markers, increased regulatory T-cells that help maintain immune balance, and better development of immune memory. Both groups cleared the virus effectively, but stem cell-treated cats maintained more normal lymphocyte counts and showed evidence of improved long-term immune function. No severe side effects were observed in either group.
Limitations
The study had a relatively small sample size, which reduces statistical power. Researchers only enrolled cats that weren’t critically ill, limiting how broadly the findings apply to severe cases. One cat’s data was excluded due to outlier results. The natural variability of the disease and lack of control groups (no treatment or stem cells alone) due to ethical considerations also constrained the analysis. Additionally, the study lacked post-treatment tissue analysis that could have further confirmed the molecular findings.