MSC Therapy Boosts Immune Recovery in Severe Coronavirus Infection

Severe coronavirus infections—including SARS-CoV-2—drive profound immune dysfunction characterized by T-cell exhaustion, lymphopenia, cytokine storms, and persistent inflammation. Effective therapies to restore immune homeostasis remain elusive. Feline infectious peritonitis (FIP), caused by a feline coronavirus, naturally recapitulates these immune pathologies in genetically diverse, immunologically intact hosts, making it an ideal translational model.

This randomized controlled trial enrolled 11 cats with naturally occurring effusive FIP, assigning them to antiviral therapy alone (GS-441524, 16–25 mg/kg orally daily for 12 weeks) or antiviral therapy combined with two intravenous infusions of 20 million allogeneic adipose-derived MSCs given two weeks apart. Comprehensive analyses included hematology, qRT-PCR viral load quantification, flow cytometry, single-cell RNA sequencing (scRNA-seq) of mesenteric lymph nodes, and 19-plex serum cytokine profiling.

Antiviral therapy was highly effective: viral loads became undetectable in all cats within one week. Both groups showed resolution of anemia, neutrophilia, and lymphopenia. However, MSC-treated cats demonstrated superior immune recovery. Flow cytometry and transcriptomic analyses showed MSC treatment reduced expression of exhaustion-related inhibitory receptors (PD-1, TIM-3, LAG-3) and exhaustion-driving transcription factors (IKZF2, ZEB2, PRDM1). Concurrently, MSC-treated cats had expanded regulatory T-cell populations and elevated memory T-cell markers (IKZF1, GZMK, IL7R) by scRNA-seq. Hyperproliferative lymphocyte subsets were also reduced, suggesting a shift from dysregulated activation toward durable immune memory.

Serum cytokine profiling using principal component analysis identified three distinct inflammatory mediator patterns. Both treatment groups transitioned toward cytokine profiles resembling healthy controls, but residual cytokine elevations persisted at week 12—mirroring chronic immune dysregulation seen in long COVID. Notably, PDGF-bb, a marker of tissue repair, was uniquely associated with higher lymphocyte counts, implicating it in lymphoid tissue recovery.

The MSC treatment was safe; no severe adverse events occurred. Minor side effects included intermittent diarrhea in a subset of cats. These findings establish FIP as a robust translational model and demonstrate that MSC therapy can meaningfully modulate viral immune dysfunction—reducing exhaustion, promoting memory formation, and restoring immune balance. The authors suggest relevance to human conditions including severe COVID-19, MIS-C, and long COVID, where similar immune pathologies persist despite viral clearance.