Faecal Microbiota Transplantation in Paediatric Haematopoietic Stem Cell Transplantation: Current Evidence, Safety, and Future Directions

Background: Haematopoietic stem cell transplantation (HSCT) can cure paediatric haematological diseases but is associated with graft-versus-host disease (GVHD), infections and treatment-related morbidity. Conditioning, antimicrobial exposure and nutritional changes disrupt the gut micro-biome, which may influence immune recovery and transplant outcomes. Faecal microbiota trans-plantation (FMT) is being investigated as a means of restoring microbial communities and function. Methods: This narrative review examines evidence on microbiome development in children, mi-crobiome alterations during cancer therapy and HSCT, associations with transplant complications, and the rationale, administration, donor screening, engraftment and safety of FMT. Paediatric HSCT studies were prioritised; adult HSCT studies and paediatric studies in other indications were con-sidered as indirect evidence where relevant. Results: Gut dysbiosis after HSCT is associated with infection, GVHD and mortality, although these associations do not establish causality. FMT may restore microbial diversity and microbial functions, but these changes do not necessarily translate into clinical benefit. Evidence in paediatric HSCT remains limited, comprising small cohorts, case reports and case series with heterogeneous indications and protocols. Paediatric FMT data for re-current Clostridioides difficile infection are more extensive but cannot establish safety or efficacy in profoundly immunocompromised transplant recipients. Potential benefits must be weighed against risks, including donor-derived infection, procedural complications and poorly characterised long-term effects. Conclusions: FMT is a promising but investigational approach in paediatric HSCT. Its routine use for transplant-associated dysbiosis or GVHD is not supported by evidence. Prospective multicentre studies with standardised protocols, clinically meaningful outcomes and long-term follow-up are needed to define indications, timing, efficacy and safety.