Abstract Body: End-stage ischemic heart disease necessitates heart transplantation, and emerging cell therapy presents a promising solution to address donor scarcity. Disruption of gut microbiota significantly influences various diseases and treatments, including transplantation. However, the impact of immunosuppression and cardiac cell therapy on gut microbiota remains largely unexplored. To elucidate this relationship, we investigated gut microbiota dynamics in response to immunosuppression and cell therapy in a nonhuman primate (NHP) cardiac ischemia/reperfusion (IR) model, with controlled genetic, dietary, and environmental factors. Immunosuppression enriched anaerobes (Faecalibacterium, Streptococcus, Anaerovibrio, Dialister), increasing gut microbiota diversity. These changes correlated with metabolic shifts towards amino acid metabolism and nucleosides/nucleotides biosynthesis. Combined treatment of human induced pluripotent stem cell (iPSC)-derived endothelial cells (EC) and cardiomyocytes (CM) also increased gut microbiota diversity, with specific genera alterations. The EC/CM co-treatment group displayed gut microbiota resembling the pre-injury group, with host metabolism shifting towards amino acid and fatty acid/lipid biosynthesis post-cell therapy. These observed microbiota changes and metabolic shifts could serve as biomarkers for monitoring cell therapy and immunosuppression outcomes, offering potential therapeutic targets to enhance efficacy.