Specific Gut Microbiome Changes in Myelodysplastic Neoplasms Linked to Inflammation

Introduction. Myelodysplastic neoplasms (MDS) encompass a heterogenous group of multi-factorial disorders, characterized by clonal expansion of somatically mutated hematopoietic stem and progenitor cells with consequent defect in their maturation leading to peripheral cytopenia. Inflammation is considered a relevant component of MDS pathogenesis by supporting the malignant clone. An altered gut microbiome might contribute to this process by activating the immune system and inducing inflammation. However, the definitive role of gut microbial changes in MDS is not yet established, whereas several groups demonstrated relevant - yet not always consistent - findings in microbial composition (Feng Z, 2024; Riello GBC, 2024). This study aims to provide a detailed analysis of the gut microbiome in MDS patients and to identify potentially targetable bacteria.

Methods. We analysed faecal samples from 24 patients with untreated MDS or chronic myelomonocytic leukemia (median age: 65,5 years [41-81], m/f=19/5) and healthy donors (n=11, median age: 59 years [54-70], m/f=4/7). Exclusion criteria were antibiotic treatment within the last 4 weeks, chronic inflammatory bowel disease and other malignant disorders. Gut microbial taxonomic profiles were generated from frozen faecal samples using 16S rRNA gene amplicon sequencing. For bioinformatic analysis, reads were quality filtered and taxonomically annotated using MAPseq. Statistical analysis included diversity comparison (observed genus richness and Shannon index) and differential abundance testing at genus level using Wilcoxon tests. Differences in gut microbiome composition were assessed by PERMANOVA of Euclidean distances and visualized using Principal Coordinate Analysis (PCoA).

Results and Discussion. Seventeen MDS patients were referred to the low-risk group (very low, low and intermediate according to IPSS-R), 5 patients - high-risk (high and very high), in 1 patient information was not available. All but one patient carried at least one MDS-typical somatic mutation (median: 3 [0-6]). The median time from the diagnosis to faecal sampling was 15 months [1-205].

Microbiome composition showed statistically significant differences between MDS and healthy subjects (p=0.018, R²=0.06, PERMANOVA). Whereas consistent with a prior report (Balaian, ASH 2022), MDS patients demonstrated a tendency for lower gut microbial diversity and richness, deeper analysis allowed us to identify specific genus alterations between cohorts. First, the relative abundance of Megasphaera and Prevotella is significantly increased in the MDS cohort (1.8% ± 0.7 vs 0.0004% ± 0.0003, p=0.007 and 12.8% ± 3.8 vs 3.3% ± 3.2, p=0.02, accordingly). Megasphera is known to induce dendritic cell maturation and both genera are able to stimulate production of pro-inflammatory cytokines, and therefore to induce the inflammatory response (Teijlingen NH, 2020), which might contribute to pyroptosis described in MDS bone marrow. Increased abundance of both genera is described in multiple inflammatory disorders. We also observed mild but statistically significant increase of Dorea in MDS patients (1.1% ± 0.1 vs 0.7% ± 0.09, p=0.03), which was especially prominent in overweight individuals (BMI ≥ 25 kg/m2). In contrast, Roseburia - a Gram-positive anaerobic bacteria, producing protective short-chain fatty acids (SCFA) and known for its anti-inflammatory properties - was significantly decreased in MDS patients (0.5% ± 0.2 vs 0.9% ± 0.2, p=0.009). Microbiota analysis in different risk groups revealed Denitrobacterium (p=0.008), Coprococcus (p=0.009, protective SCFA-producing bacteria), Desulfovibrio (p=0.03), Clostridium (p=0.03) and Bifidobacterium (p=0.04) to be significantly decreased in the high-risk compared to the low-risk group.

Conclusions. We demonstrated significant taxonomic changes in gut microbial composition in MDS, which might predispose or induce an inflammatory state and thereby contribute to leukemic development. Further studies appear promising to determine whether directly targeting specific bacteria might modulate the disease course.

Balaian:Novartis: Other: Travel Support. Bornhaeuser:MSD Sharp and Dohme: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees.