In human health, the function of the microbioma is to maintain a dynamic equilibrium with the host, playing both local and remote roles in important physiological processes, particularly inflammation, and immune response. The host and its microbioma constitute the “holobiont”.

Recently, it has become clear that, besides physiological mutual interactions between the host and microbioma, the microbioma is implicated in complex relations between oncogenesis, cancer development, suppression of immune response to tumor cells, inflammation and response to cancer drugs, while intestinal epithelial disruption leading to “leaky gut” condition plays a key role in low-level systemic inflammation, endotoxemia, and possibly oncogenesis.

Recent advances suggest a role for microbiome in hematological malignancies. Significant alterations of the microbiome were found in patients with leukemia, lymphoma, and myeloma, related to inflammation status and chemotherapy. The microbial metabolic effect has been suggested as a key element to achieve antitumor effects, modulating immune checkpoint blockades (ICBs) response and finely tuning adoptive T-cell function after administration of CAR-T cells and other cellular therapies.

Microbioma is also thought to influence the onset of Graft versus Host Disease after allogeneic stem cell transplantation. Supplementation with probiotics and prebiotics is under investigation to support and modulate immune response during the treatment of hematological malignancies and Fecal microbiota transplantation (FMT) is studied to restore eubiosys in patients with acute intestinal GVHD.

Due to growing evidence, the interconnection between hematological malignancies, therapeutic strategies aiming at their eradication and the role of microbioma is of vital importance. In this research topic, we welcome original articles, reviews, and bioinformatic studies that discuss the interactions between microbioma and tumorigenesis in the hematological setting, as well as the regulatory effects of the microbiota-metabolites axis on tumor epigenetics and immunoregulation, on GVHD, and efficacy and toxicity of immunotherapy and cell therapy.

We also welcome clinical or translational studies on the application of FMT in GVHD. Topics of interest include, but are not limited to, the following sections:

1. Mechanisms of gut microbiota affecting the development of hematological malignancies.

2. Impact of microbiota on effectiveness and toxicity of hematopoietic stem cells transplantation, including GVHD.

3. Application of FMT in hematological diseases and hematopoietic stem cells transplantation.

4. Interaction between microbiota and drugs used in hematological malignancies.

5. Correlation between microbiota and immune and cellular therapies, such as CAR-T therapies.

6. Hypothesis and experiences with probiotics, prebiotics, and symbiotics in hematological malignancies.

7. Mechanisms of crosstalk between host and microbiota in hematological malignancies, including the role of extracellular vesicles.

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Frontiers in Hematology

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