Gut Microbiome Modulation and Faecal Microbiota Transplantation Following Allogenic Hematopoietic Stem Cell Transplantation

Simple Summary Allogenic hematopoietic stem cell transplantation (allo-HSCT) represents a significant part of the treatment for hematologic malignancies and other types of diseases. Allo-HSCT-related complications, such as conditioning chemotherapy, graft-versus-host disease, mucositis, irradiation, administration of antibiotics, recurrent Clostridioides difficile infection, and many others, can alter the gut microbiota composition, leading to its imbalance. Consequently, the disruption of gut microbiota homeostasis and loss of gut-barrier integrity affect therapy efficacy. Thus, restoring gut microbiota diversity and maintaining its balance seem to be strongly needed in these cases. Promising effects were observed after fecal microbiota transplantation (FMT). Notwithstanding, FMT efficacy was confirmed in Clostridium difficile infection treatment in HSCT recipients. Gut microbiota may be also modified by prebiotics, probiotics, synbiotics, and postbiotics. However, the administration of fungal probiotics is associated with the risk of fungemia/septicemia, especially in immunocompromised patients. Nowadays, allogenic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy that is mainly recommended for hematologic malignancies. However, complications (such as graft-versus-host disease, mucositis, disease relapse, and infections) associated with the HSCT procedure contribute to the development of gut microbiota imbalance, gut-barrier disruption, and increased intestinal permeability. In the present narrative review, the crosstalk between gut microbiota products and intestinal homeostasis is discussed. Notably, gut-microbiota-related aspects have an impact on patients' clinical outcomes and overall survival. In accordance with the most recent published data, gut microbiota is crucial for the treatment effectiveness of many diseases, not only gastrointestinal cancers but also hematologic malignancies. Therefore, it is necessary to indicate a therapeutic method allowing to modulate gut microbiota in HSCT recipients. Currently, fecal microbiota transplantation (FMT) is the most innovative method used to alter/restore gut microbiota composition, as well as modulate its activity. Despite the fact that some previous data have shown promising results, the knowledge regarding FMT in HSCT is still strongly limited, except for the treatment of Clostridium difficile infection. Additionally, administration of prebiotics, probiotics, synbiotics, and postbiotics can also modify gut microbiota; however, this strategy should be considered carefully due to the high risk of fungemia/septicemia (especially in case of fungal probiotics).