Basic Molecular Biology, Metabolic and Immunological Mechanisms of Fecal Microbiota Transplantation

Aim: demonstration of basic molecular biological, metabolic and immunological effects of fecal microbiota transplantation (FMT), on the example of a rare case of acute graft-versus-host disease (GVHD) with intestinal damage in a patient after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Materials and methods. To monitor the basic effects of FMT, we performed targeted DNA sequencing of 16S rRNA gene (V3–V4) using MiSeq platform as well as multiplex real-time PCR, MS/gas chromatography technique, immunophenotyping of blood lymphocytes, histological and immunohistochemical techniques. Clinical case. A 40-year-old female patient diagnosed with myelodysplastic syndrome, with a history of two unsuccessful allo-HSCTs due to graft failure, underwent the third haploidentical HSCT (haplo-HSCT) from her father as ‘salvage’ therapy. Due to early viral/bacterial colitis post-transplant associated with a multidrug-resistant strain of K. pneumoniae and herpes virus type 6, FMT was performed on days 46 and 47 after allo-HSCT. Complete resolution of the enteropathy symptoms was noted following FMT. However, immunosuppressive therapy was canceled on D+106 after haplo-HSCT due to the detection of minimal residual disease causing development of the ‘overlap’-type GVHD with damage skin lesions grade 4, and intestinal mucous membranes grade 3. This complication required resumption and subsequent intensification of immunosuppressive therapy with complete resolution of GVHD symptoms. Following FMT treatment, the patient showed complete resolution of clinical colitis symptoms. According to results of 16S rRNA sequencing, the species-specific diversity of fecal microbiota increased significantly, along with decreased relative contents of opportunistic bacteria ( Klebsiella, Enterococcus, Streptococcus genera). A significant growth was revealed for commensal Bacteroidota , and re-emergence of Faecalibacterium, Blautia, Roseburia . Acute gastrointestinal GVHD promoted by tacrolimus withdrawal was associated with repeated depletion of intestinal microbiota. Upon resolution of GVHD and resumed immunosuppression, increased microbiota diversity (Shannon index) was again recorded, and the parameters of patient’s fecal microbiota reached the donor values. The microbiota shifts at all clinical stages (before and after FMT, at the peak of acute intestinal GVHD and intensive immunosuppressive therapy) showed some relations with metabolism of bile and fatty acids in blood plasma and immune parameters. Conclusions. FMT may be a component of complex therapy aimed at early reconstitution of immune system and organic acid metabolism in patients after allo-HSCT. The composition of fecal microbiota, metabolic profile and spectrum of lymphocyte subpopulations may be markers for monitoring complex rehabilitation after allo-HSCT.