Summary:
This study looked at why some rare cases of heart inflammation (myocarditis) happen after COVID-19 mRNA vaccines, especially in young men after the second dose. Researchers studied human blood samples and lab experiments with human immune and heart cells. They found that two immune signaling proteins, CXCL10 and interferon-gamma (IFN-γ), increased after vaccination. In experiments with mice, blocking these proteins around the time of the second dose reduced heart injury and lowered markers of heart stress. Lab-grown human heart cells exposed to these proteins showed weaker contraction, irregular heartbeats, and inflammation. A plant compound called genistein, which can reduce heart inflammation, lessened these effects in the lab. In mice, genistein also reduced heart damage and immune cell infiltration after vaccination. These findings suggest that CXCL10 and IFN-γ play a role in vaccine-related heart inflammation, and therapies that reduce heart inflammation may be preventive.
Abstract:
Messenger RNA (mRNA) vaccines against SARS-CoV-2 are highly effective and were instrumental in curbing the COVID-19 pandemic. However, rare cases of noninfective myocarditis, particularly in young males and typically after the second dose, have been observed. Here, we explore the mediators of this myocarditis to better understand and to enhance the safety of future mRNA vaccines. Through analysis of human plasma data and in vitro experiments with human macrophages and T cells, we identified increased C-X-C motif chemokine ligand 10 (CXCL10) and interferon-γ (IFN-γ) after exposure to BNT162b2 (Pfizer) or mRNA-1273 (Moderna). Neutralization of CXCL10 and IFN-γ during the second dose (21 days after the first dose) reduced vaccine-induced cardiac injury in mice. Neutralization also reduced cardiac stress markers such as the release of N-terminal pro-B-type natriuretic peptide (NT-proBNP) and expression of inflammatory genes in human induced pluripotent stem cell (iPSC)–derived cardiac spheroids. When exposed to these cytokines in vitro, human iPSC-derived cardiomyocytes (iPSC-CMs) exhibited impaired contractility, arrhythmogenicity, and proinflammatory gene expression patterns. Genistein, a phytoestrogen implicated in reducing cardiovascular inflammation, mitigated these effects in iPSC-CMs. In mice exposed to these cytokines or receiving BNT162b2 vaccination, genistein treatment reduced cardiac injury markers and attenuated infiltration of neutrophils and macrophages into the heart. These findings implicate CXCL10–IFN-γ signaling as a contributor to myocardial injury in experimental models of mRNA vaccination and indicate that pharmacologic modulation, such as with genistein, may mitigate cytokine-driven injury.
Article Publication Date: 10/12/2025
DOI: 10.1126/scitranslmed.adq0143
