2. Microbiome Environments and Lymphomagenesis
Animal models provide a useful tool in determining the intricate relationship between the gut microbiome and health and disease; in particular, the importance of the microbiota in immune development and composition, as well as its role in carcinogenesis
[16][10]. Investigators have demonstrated its significant contribution to disease progression and the eradication of organisms such as
Staphylococcus aureus, with improved outcomes in cutaneous T-cell lymphoma (CTCL)
[17][11]. Tegla et al. also demonstrated the increased colonization of
Staphylococcus spp. via CTCL microbiome analysis, when compared with healthy controls. This suggests a potential role of the dominance of
S. aureus, leading to direct enhanced antigen presentation, enhanced clonal expansion of T cells, and the upregulation of pro-inflammatory cytokines, contributing to disease progression in CTCL
[17][11]. Broad-spectrum antibiotics used in the treatment of advanced-stage CTCL lesions were associated with tumor regression and a reduction in the fraction of malignant T cells, suggesting that the microbiota can contribute to lymphoma pathogenesis
[18][12].
Primary lymphomas that recapitulate the features of gastric mucosa-associated lymphoid tissue lymphoma (gastric MALT lymphoma) are known to arise in the stomach
[19,20][13][14]. Epidemiologically, gastric MALT lymphoma is closely associated with the infection of a specific bacteria,
Helicobacter pylori [21][15]. While
H. pylori is present in approximately 50% of the world’s population
[21][15], the incidence of gastric MALT lymphoma is low, suggesting that there are specific mechanisms by which
H. pylori invades the gastric mucosa and, subsequently, evades the host immune system. The first study to investigate and further elucidate this link was conducted by Wotherspoon et al. In this study, the investigators showed that
H. pylori infection significantly increased the risk of gastric MALT lymphoma, due to the vast majority of these patients being infected with
H. pylori [19][13]. Furthermore, this study observed that the lymphoid follicles in these
H. pylori-infected individuals developed into lymphoid tissues that were morphologically identical to gastric MALT lymphoma
[19][13]. In 1993, Wotherspoon et al. further characterized the role of
H. pylori in gastric MALT lymphoma using six patients, all of whom showed histological and genetic evidence of gastric MALT lymphoma. Remarkably, treatment with antibiotics led to the eradication of
H. pylori infection and the subsequent regression of the lymphoma in the majority of the study population
[22][16]. Since then,
H. pylori infection and the different mechanisms contributing to the genesis of gastric MALT lymphoma have been revealed. Tumor-infiltrating T cells that are stimulated by
H. pylori antigens have been shown to enhance the growth of B cells in gastric MALT lymphoma
[23][17]. Additionally, another study showed that antigen-dependent development and the subsequent progression of gastric MALT lymphoma may be triggered by the expression of the CD40 ligand, in concert with Th2 cytokines, IL-4, and IL-10, by activated T cells
[24][18]. These studies highlight the intricate communication between microbes, T cells, and B cells in the pathogenesis of MALT lymphoid malignancies and suggest that the balance of immune-activating and immune-suppressing cell populations and their signals contributes to the unique features in MALT lymphoma, including susceptibility to antibiotic-driven strategies.
Specific tumor-infiltrating T cells and B cell receptor (BCR) signaling also play a role in the pathogenesis of gastric MALT lymphoma. In a study conducted by Craig et al., investigators used a murine model of
H. felis-induced gastric MALT lymphoma to show that the development of MALT lymphoma requires both BCR signaling, via the poly-reactivation of tumor-derived immunoglobulins (Igs) with self-antigens, and tumor-infiltrating CD4+ T cells
[25][19]. Moreover, most of these CD4+ T cells were FOXP3+ regulatory T cells that were being recruited by the tumor cells via chemokines such as CCL17 and CCL22
[25][19]. The in vivo inhibition of FOXP3+ regulatory T cells indeed resulted in the regression of gastric MALT lymphoma
[25][19]. In line with this finding, Garcia et al. showed a higher FOXP3+/CD3+ cell ratio in
H. pylori-positive gastric MALT lymphoma than in
H. pylori-negative gastric MALT lymphoma
[26][20]. Additionally, the expression of CD86, a co-stimulatory molecule that activates B cells to proliferate and produce IgG in B-cell lymphoma, was shown to be significantly associated with the sensitivity of
H. pylori-dependent gastric MALT lymphoma to
H. pylori eradication
[27][21]. As illustrated in
Figure 1, we demonstrate the intertwined relationship involving the gut microbiome, lymphomagenesis, lymphoma-directed therapies, and microbial interventions, details of which will be given later in this article.
Figure 1. The intertwined relationship between the gut microbiome, lymphomagenesis, lymphoma-directed therapies, and microbiome-directed interventions. This illustration depicts the relationship between the gut microbiome, lymphoid malignancies, and microbiome therapeutics. The examples of microbiome therapeutics that are provided demonstrate how these approaches change key features and readouts of the gut microbiome. These changes in the microbiome not only influence lymphoid malignancies directly but also affect the therapies used to treat them, including immune cellular therapies such as CAR T-cell therapy, potentially through the emerging role of the tumor microbiome. SCFA, short-chain fatty acid; CAR T cell, chimeric antigen receptor T cell; auto-SCT, autologous stem-cell transplant; allo-HSCT, allogeneic hematopoietic stem-cell transplant; HL, Hodgkin’s lymphoma; MALT, mucosa-associated lymphoid tissue; MM, multiple myeloma; CLL, chronic lymphocytic leukemia; TME, tumor microenvironment; BM, bone marrow; LN, lymph node.