Fecal microbiota transplantation: from empirical remedy to precision medicine.

Fecal microbiota transplantation (FMT) has evolved from an empirical remedy for recurrent Clostridioides difficile infection (rCDI) into a foundational platform for precision microbiome-based therapeutics. This comprehensive review details FMT's journey, analyzing its multifaceted mechanisms of action-including restoration of colonization resistance, metabolic reprogramming via short-chain fatty acids and bile acids, and profound immunomodulation-which extend far beyond simple microbial replacement. We critically evaluate its established, high efficacy in rCDI and its expanding, albeit more variable, applications across a wide spectrum of gastrointestinal diseases (such as inflammatory bowel disease, irritable bowel syndrome, and constipation), neurological disorders (including Parkinson's and Alzheimer's disease), metabolic conditions, autoimmune diseases, and oncology (particularly in modulating response to immune checkpoint inhibitors and treating graft-versus-host disease). The review further discusses the critical challenges of donor-recipient variability, safety, and the lack of standardized protocols that have driven the field's technical evolution. This progression encompasses refined processing methods like washed microbiota transplantation (WMT), diverse delivery routes including oral capsules, and the exploration of non-bacterial components like bacteriophages through fecal filtrate transplantation (FVT). Ultimately, we highlight the field's trajectory toward next-generation, defined live biotherapeutic products (LBPs) and engineered microbial consortia, aiming to transition from the complex "black box" of whole stool to safer, more consistent, and rationally designed precision therapies that target the specific dysbiotic networks underlying diverse human diseases.