Gut Microbiome Composition Is Associated with Engraftment Syndrome in Multiple Myeloma Patients Undergoing Autologous Stem Cell Transplantation

Background: Engraftment syndrome (ES) is a pro-inflammatory complication often seen during neutrophil recovery in MM patients treated with high-dose melphalan conditioning chemotherapy and autologous stem cell transplantation (ASCT). The varied incidence of ES (5-70%) reported by different transplant centers is due to stringent diagnostic criteria and a myriad of symptoms (e.g. diarrhea, non-infectious fever, skin rash, capillary leak). Most ES cases are mild whereas a subset of patients is at higher risk of morbidity, longer hospital stay, infection, and occasional death. The etiology of ES remains elusive and probable mechanisms include proinflammatory cytokines, endothelial dysfunction, and activation of self-reactive T cells, all reminiscent of graft-versus host disease. Current induction regimens consisting of IMiDs and proteasome inhibitors have been associated with the increased the incidence of ES in MM patients. Gut microbiome composition is associated with immune-related adverse events and response to immune checkpoint blockade, allogeneic stem cell transplantation, ASCT and CAR T cell therapy. In MM, loss of gut microbiota (GM) diversity and domination of Enterococcus and Streptococcus during engraftment predicted inferior outcomes post-ASCT. A higher abundance of butyrate-producing Eubacterium hallii was associated with minimal residual disease negativity. In this prospective observational study, we hypothesize that depletion of healthy gut commensals and mono-domination of facultative pathogens may influence the development of ES.

Methods and Results: We serially collected stools samples from 53 MM patients at time of melphalan conditioning (pre-ASCT), engraftment (72hrs of absolute neutrophil count ≥ 500/mcL), and 60-120 days post-ASCT. Taxonomic profiling was performed using 16S rRNA sequencing of the V4-V5 region and amplicon sequence variants (ASV) were annotated against the NCBI 16S database using BLAST. We found lower alpha-diversity at neutrophil engraftment from pre-ASCT, using inverse Simpson diversity index (p=0.0001, Wilcoxon matched pairs signed rank test, n=45). Recovery of diversity to pre-ASCT levels was attained 60-120 days post-ASCT (p=0.001, n=41). However, we did not observe any significant differences in alpha-diversity of patients with ES and without ES at each timepoint tested (Fig.1A). The domination taxa profiles (defined as the relative abundance of a single taxon >30%) differed between patients with and without ES at each timepoint (Fig. 1B). The domination of Enterococcus was only evident in ES patients (pre-ASCT, engraftment) whereas Streptococcus was unique to non-ES patients (engraftment, post-ASCT). Blautia had a higher frequency of domination in non-ES patients compared to ES patients prior to ASCT, during engraftment and post-ASCT. Using Random Forest, a supervised machine-learning algorithm, Streptococcus, Ruminococcus, Coprococcus, and Enterococcus had the highest variable significant features at engraftment.

Conclusions: We found that domination of Enterococcus prior to conditioning and ASCT and further increasing during engraftment is associated with increased risk of ES. Our findings suggest that GM may impact immune-related adverse events and outcomes in MM patients undergoing ASCT and provide the rationale for microbiota-centered interventions.