Associations Between the Gut Microbiome and Outcomes in Autologous Stem Cell Transplantation: A Systematic Review

Autologous stem cell transplantation (ASCT) is the standard frontline consolidation strategy in fit, eligible patients with chemosensitive multiple myeloma, and it also serves as salvage option in other haematological malignancies, such as diffuse large B cell lymphoma. Moreover, ASCT is known to disrupt the gut microbiome (GM), and the impact on clinical outcomes has been understudied. The aim of this review is to examine the associations between the GM and outcomes in patients undergoing ASCT. Using the PRISMA 2020 guidelines for systematic reviews and meta-analyses, a total of 11 articles were included in this review, comprising both observational studies (cohort studies, case-control studies) and interventional trials (randomised controlled trials). Consistent findings included a notable decrease in beneficial bacteria, including Bacteriodetes, Firmicutes and Faecalibacterium prausnitzii, which maintain gut homeostasis and modulate immune responses. Conversely, an increase in pathogenic bacteria, including Escherichia coli, Enterococcus spp. and Klebsiella spp., was observed post-transplantation. This review includes an overview of the GM following ASCT and the techniques commonly used to assess it, and highlights gaps, thereby identifying key areas for future research, although conclusions are limited by variation in sample size and reporting inconsistencies. Understanding the GM's role in ASCT may lead to interventions that optimise patient outcomes through therapeutic manipulation of the GM.