Effects of postoperative adjuvant chemotherapy and palliative chemotherapy on the gut microbiome in colorectal cancer

The Role of the Gut Microbiome in Non-Hodgkin Lymphoma (NHL): A Focus on Diffuse Large B-Cell Lymphoma, Follicular Lymphoma, Cutaneous T-Cell Lymphoma, and NK/T-Cell Lymphoma

Non-Hodgkin lymphomas (NHLs) encompass a diverse group of neoplasms arising from the clonal proliferation of B-cell progenitors, T-cell progenitors, mature B-cells, mature T-cells, and natural killer (NK) cells. These malignancies account for over 90% of lymphoid neoplasms. The link between the gut microbiome and neoplasms has been extensively studied in recent years. Growing evidence suggests that the gut microbiome may be involved not only in the development of the disease, but also in modulating the efficacy of implemented therapies. In this review, we summarize the current knowledge on the potential involvement of the gut microbiome in the development of diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), mucosa-associated lymphoid tissue (MALT) lymphoma, and NK/T-cell lymphoma, including cutaneous T-cell lymphoma (CTCL). Moreover, we discuss the relationship between gut microbiome changes before and after treatment and their association with treatment outcomes, focusing on chemotherapy and CAR T-cell therapy.

The Role of the Microbiome in Cancer Therapies: Current Evidence and Future Directions

The microbiome is essential for maintaining human health and is also a key factor in the development and progression of various diseases, including cancer. Growing evidence has highlighted the microbiome's significant impact on cancer development, progression, and treatment outcomes. As research continues to unfold, the microbiome and its modulation stand out as a promising frontier in cancer research and therapy. This review highlights current literature on the interplay between various cancer treatment modalities and human microbiotas, focusing on how the microbiome may affect treatment efficacy and toxicity and its potential as a therapeutic target to enhance future outcomes.

Exploring the Impact of Chemotherapy on the Emergence of Antibiotic Resistance in the Gut Microbiota of Colorectal Cancer Patients

With nearly half of colorectal cancer (CRC) patients diagnosed at advanced stages where surgery alone is insufficient, chemotherapy remains a cornerstone for this cancer treatment. To prevent infections and improve outcomes, antibiotics are often co-administered. However, chemotherapeutic interactions with the gut microbiota cause significant non-selective toxicity, affecting not only tumor and normal epithelial cells but also the gut microbiota. This toxicity triggers the bacterial SOS response and loss of microbial diversity, leading to bacterial mutations and dysbiosis. Consequently, pathogenic overgrowth and systemic infections increase, necessitating broad-spectrum antibiotics intervention. This review underscores how prolonged antibiotic use during chemotherapy, combined with chemotherapy-induced bacterial mutations, creates selective pressures that drive de novo antimicrobial resistance (AMR), allowing resistant bacteria to dominate the gut. This compromises the treatment efficacy and elevates the mortality risk. Restoring gut microbial diversity may mitigate chemotherapy-induced toxicity and improve therapeutic outcomes, and emerging strategies, such as fecal microbiota transplantation (FMT), probiotics, and prebiotics, show considerable promise. Given the global threat posed by antibiotic resistance to cancer treatment, prioritizing antimicrobial stewardship is essential for optimizing antibiotic use and preventing resistance in CRC patients undergoing chemotherapy. Future research should aim to minimize chemotherapy's impact on the gut microbiota and develop targeted interventions to restore microbial diversity affected during chemotherapy.

Colorectal cancer in Lynch syndrome families: consequences of gene germline mutations and the gut microbiota

BACKGROUND

Lynch syndrome (LS)-associated colorectal cancer (CRC) always ascribes to pathogenic germline mutations in mismatch repair (MMR) genes. However, the penetrance of CRC varies among those with the same MMR gene mutation. Thus, we hypothesized that the gut microbiota is also involved in CRC development in LS families.

METHODS

This prospective, observational study was performed from December 2020 to March 2023. We enrolled 72 individuals from 9 LS families across six provinces in China and employed 16S rRNA gene amplicon sequencing to analyze the fecal microbiota components among LS-related CRC patients (AS group), their spouses (BS group), mutation carriers without CRC (CS group), and non-mutation carriers (DS group) using alpha and beta diversity indices.

RESULTS

There were no apparent differences in age or gender among the four groups. Alpha and beta diversity indices exhibited no significant differences between the AS and BS groups, verifying the role of germline mutations in the occurrence of CRC in LS families. Beta diversity analysis exhibited significant differences between the AS and CS groups, revealing the importance of the gut microbiota for the occurrence of CRC in LS families. A greater difference (both alpha and beta diversity indices) was shown between the AS and DS groups, demonstrating the combined impact of the gut microbiota and genetic germline mutations on the occurrence of CRC in LS families. Compared with those in the CS and DS groups, we identified ten microbial genera enriched in the AS group, and one genus (Bacteroides) decreased in the AS group. Among the elevated genera in the AS group, Agathobacter, Coprococcus and Prevotellaceae_NK3B31_group were butyrate-producing genera.

CONCLUSION

This study found the development of CRC in the LS families can be attributed to the combined effects of gene germline mutations as well as the gut microbiota and provided novel insights into the prevention and treatment of CRC in the LS families.

Gut Microbiome Changes After Neoadjuvant Chemotherapy and Surgery in Patients with Gastric Cancer

BACKGROUND/OBJECTIVES

Neoadjuvant chemotherapy (NAC) followed by radical gastrectomy is the current standard approach for locally advanced gastric cancer (GC) in the West. Both NAC and gastrectomy can significantly influence the gut microbiome, potentially leading to clinically significant changes. However, no longitudinal studies to date support this hypothesis. This study investigates gut microbiome changes throughout GC treatment, including NAC and gastrectomy.

METHODS

This longitudinal observational study included GC patients undergoing NAC followed by gastrectomy. Fecal microbiome composition, intestinal inflammation (fecal calprotectin), and gut permeability (LBP, sCD14) markers were investigated at baseline, after NAC, and after gastrectomy.

RESULTS

A total of 38 patients were included in the study. The results showed that NAC did not affect the gut microbiome composition at the phylum level. In contrast, radical gastrectomy led to an increased abundance of Bacteroidetes and Proteobacteria and a decreased abundance of Firmicutes and Actinobacteria. Furthermore, NAC alone did not impact alpha or beta diversity, while a combination of NAC and gastrectomy significantly influenced both. After gastrectomy, the gut microbiome composition analysis also revealed enrichment of oralization-associated bacterial species such as Escherichia-Shigella, Streptococcus equinus, uncultured Streptococcus species, and species from the Enterobacteriaceae family. Intestinal inflammation and gut permeability markers did not significantly change throughout the treatment.

CONCLUSIONS

The radical treatment of advanced GC with NAC and radical surgery has long-term effects on the gut microbiome, characterized by gut microbiome oralization. These sustained alterations primarily stem from the radical gastrectomy rather than the NAC. Since previous studies have linked oralization-associated dysbiosis to various gastrointestinal symptoms, this study highlights the gut microbiome as a potential therapeutic target to enhance the quality of life in long-term survivors following gastrectomy.

A greener side of health care: Revisiting phytomedicine against the human fungal pathogen Malassezia

Malassezia species are commensal fungi residing on the skin and in the gut of humans and animals. Yet, under certain conditions, they become opportunistic pathogens leading to various clinical conditions including dermatological disorders. The emergence of drug resistance and adverse effects associated with conventional antifungal agents has propelled the search for alternative treatments, among which phytomedicine stands out prominently. Phytochemicals, including phenolic acids, flavonoids, and terpenoids, demonstrate potential antifungal activity against Malassezia by inhibiting its growth, adhesion, and biofilm formation. Furthermore, the multifaceted therapeutic properties of phytomedicine (including anti-fungal and, antioxidant properties) contribute to its efficacy in alleviating symptoms associated with Malassezia infections. Despite these promising prospects, several challenges hinder the widespread adoption of phytomedicine in clinical practice mostly since the mechanistic studies and controlled experiments to prove efficacy have not been done. Issues include standardization of herbal extracts, variable bioavailability, and limited clinical evidence. Hence, proper regulatory constraints necessitate comprehensive research endeavors and regulatory frameworks to harness the full therapeutic potential of phytomedicine. In conclusion, while phytomedicine holds immense promise as an alternative or adjunctive therapy against Malassezia, addressing these challenges is imperative to optimize its efficacy and ensure its integration into mainstream medical care. In this review we provide an update on the potential phytomedicines in combating Malassezia-related ailments, emphasizing its diverse chemical constituents and mechanisms of action.

The role of gut microbiota and metabolites in cancer chemotherapy

BACKGROUND

The microbiota inhabits the epithelial surfaces of hosts, which influences physiological functions from helping digest food and acquiring nutrition to regulate metabolism and shaping host immunity. With the deep insight into the microbiota, an increasing amount of research reveals that it is also involved in the initiation and progression of cancer. Intriguingly, gut microbiota can mediate the biotransformation of drugs, thereby altering their bioavailability, bioactivity, or toxicity.

AIM OF REVIEW

The review aims to elaborate on the role of gut microbiota and microbial metabolites in the efficacy and adverse effects of chemotherapeutics. Furthermore, we discuss the clinical potential of various ways to harness gut microbiota for cancer chemotherapy.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Recent evidence shows that gut microbiota modulates the efficacy and toxicity of chemotherapy agents, leading to diverse host responses to chemotherapy. Thereinto, targeting the microbiota to improve efficacy and diminish the toxicity of chemotherapeutic drugs may be a promising strategy in tumor treatment.

Impact of the gut microbiome on response and toxicity to chemotherapy in advanced esophageal cancer

Objective

To identify the gut bacteria associated with chemotherapeutic outcomes, t characterized the gut microbiota in patients with esophageal squamous cell carcinoma (ESCC) in this prospective study.

Design

Thirty-one patients with ESCC were enrolled. Chemotherapy was performed with paclitaxel and cisplatin (TP). Fecal samples were collected before and after treatment and analyzed using 16S rRNA sequencing.

Results

The species with differences in baseline abundance between partial response (PR) and non-PR groups was identified as Bacteroides plebeius (P = 0.043). The baseline abundance of B. plebeius was higher in the responder (R, PR + stable disease (SD)) group (P = 0.045) than in the non-responder (NR). The abundance of B. ovatus was identified as a predictor for distinguishing patients with PR from those without PR (sensitivity, 83.3 %; specificity, 69.6 %). The abundance of B. plebeius was positively associated with the response to PR + SD (R) in predicting responders in the receiver operating characteristic (ROC) curve analysis (area under the ROC curve = 0.865, P = 0.041). The abundance of B. plebeius and B.uniform was a predictor of grade (G) 3-4 chemotherapy toxicities. The sensitivity and specificity of the established multi-analyte microbial predictive model demonstrated a better predictive ability than a single parameter (B. uniform or B. plebeius).

Conclusion

The abundance of gut microbiota B. plebeius and B. ovatus are associated with the efficacy of TP chemotherapy in patients with ESCC. The abundance of B. plebeius and B.uniform may related to the toxicity of TP chemotherapy.

High incidence of gallstones after Roux-en-Y reconstruction gastrectomy in gastric cancer: a multicenter, long-term cohort study

BACKGROUND

Roux-en-Y reconstruction is a common anastomosis technique during gastrectomy in gastric cancer. There is a lack of studies on gallstones after Roux-en-Y reconstruction gastrectomy. This study investigated the incidence and potential risk factors associated with gallstones after Roux-en-Y reconstructive gastrectomy in gastric cancer.

METHODS

The study analyzed data from gastric cancer who underwent radical gastrectomy and Roux-en-Y reconstruction at two hospitals between January 2014 and December 2020. The patients fall into distal and total gastrectomy groups based on the extent of gastrectomy. The cumulative event probability curve was plotted using the Kaplan-Meier, and differences in gallstone between groups were evaluated using the Log-Rank. Propensity score matching was applied to construct a balanced total versus distal gastrectomies cohort. A Cox regression was employed to analyze the risk factors for gallstones after Roux-en-Y reconstructive gastrectomy in gastric cancer. Further subgroup analysis was performed.

RESULTS

Five hundred thirty-one patients were included in this study, 201 in the distal gastrectomy group and 330 in the total gastrectomy. During the follow-up, gallstones occurred in 170 cases after gastrectomy, of which 145 cases accounted for 85.29% of all stones in the first two years after surgery. Then, to reduce the impact of bias, a 1:1 propensity score matching analysis was performed on the two groups of patients. A total of 344 patients were evaluated, with each subgroup comprising 172 patients. In the matched population, the Cox regression analysis revealed that females, BMI ≥23 kg/m 2 , total gastrectomy, No.12 lymph node dissection, and adjuvant chemotherapy were risk factors for gallstones after Roux-en-Y reconstructive gastrectomy. Subgroup analysis showed that open surgery further increased the risk of gallstones after total gastrectomy.

CONCLUSION

The incidence of gallstones increased significantly within 2years after Roux-en-Y reconstructive gastrectomy for gastric cancer. Patients with these risk factors should be followed closely after gastrectomy to avoid symptomatic gallstones.

Potential therapeutic target for polysaccharide inhibition of colon cancer progression

In recent years, colon cancer has become one of the most common malignant tumors worldwide, posing a great threat to human health. Studies have shown that natural polysaccharides have rich biological activities and medicinal value, such as anti-inflammatory, anti-cancer, anti-oxidation, and immune-enhancing effects, especially with potential anti-colon cancer mechanisms. Natural polysaccharides can not only protect and enhance the homeostasis of the intestinal environment but also exert a direct inhibition effect on cancer cells, making it a promising strategy for treating colon cancer. Preliminary clinical experiments have demonstrated that oral administration of low and high doses of citrus pectin polysaccharides can reduce tumor volume in mice by 38% (p < 0.02) and 70% (p < 0.001), respectively. These results are encouraging. However, there are relatively few clinical studies on the effectiveness of polysaccharide therapy for colon cancer, and ensuring the effective bioavailability of polysaccharides in the body remains a challenge. In this article, we elucidate the impact of the physicochemical factors of polysaccharides on their anticancer effects and then reveal the anti-tumor effects and mechanisms of natural polysaccharides on colon cancer. Finally, we emphasize the challenges of using polysaccharides in the treatment of colon cancer and discuss future applications.

Microbiome in Cancer Development and Treatment

Targeting the microbiome, microbiota-derived metabolites, and related pathways represents a significant challenge in oncology. Microbiome analyses have confirmed the negative impact of cancer treatment on gut homeostasis, resulting in acute dysbiosis and severe complications, including massive inflammatory immune response, mucosal barrier disruption, and bacterial translocation across the gut epithelium. Moreover, recent studies revealed the relationship between an imbalance in the gut microbiome and treatment-related toxicity. In this review, we provide current insights into the role of the microbiome in tumor development and the impact of gut and tumor microbiomes on chemo- and immunotherapy efficacy, as well as treatment-induced late effects, including cognitive impairment and cardiotoxicity. As discussed, microbiota modulation via probiotic supplementation and fecal microbiota transplantation represents a new trend in cancer patient care, aiming to increase bacterial diversity, alleviate acute and long-term treatment-induced toxicity, and improve the response to various treatment modalities. However, a more detailed understanding of the complex relationship between the microbiome and host can significantly contribute to integrating a microbiome-based approach into clinical practice. Determination of causal correlations might lead to the identification of clinically relevant diagnostic and prognostic microbial biomarkers. Notably, restoration of intestinal homeostasis could contribute to optimizing treatment efficacy and improving cancer patient outcomes.

Changes of gut microbiota in colorectal cancer patients with Pentatrichomonas hominis infection

Pentatrichomonas hominis is a parasitic trichomonads protozoa that parasitizes in the colon and cecum of humans and other animals. Our previous studies have demonstrated that infection with P. hominis is associated with the incidence of colon cancer (37.93%). However, the mechanism by which P. hominis infections increase the incidence of colon cancer remains unclear. Previous studies have suggested that certain parasites promote colon cancer by regulating gut microbiota. This study aimed to elucidate whether the association between P. hominis infections and the increased incidence of colon cancer is related to changes in gut microbiota. Therefore, the gut microbiota patients with colon cancer who were infected with P. hominis and uninfected patients with colon cancer were analyzed by 16S rRNA high-throughput sequencing. The results demonstrated that patients with colon cancer who were not infected with P. hominis showed increased gut bacterial diversity, a higher relative abundance of Alcaligenes sp., Leucobacter sp., Paraprevotella sp., Ruminococcaceae UCG-002, and a significant reduction in the abundance of Veillonella sp., compared to individuals without colon cancer. Additionally, the relative abundance of the Ruminococcaceae UCG-002 and the Eubacterium eligens groups was reduced, while the relative abundance of bacteria associated with colon cancer, including Flavonifractor sp., Lachnoclostridium sp., and the Ruminococcus gnavus group, increased significantly in patients with colon cancer who were infected with P. hominis, compared to those of uninfected patients with colon cancer. In conclusion, these results suggested that P. hominis infections may aggravate the development of colon cancer and the findings provide new insights for subsequent in-depth studies on the pathogenesis, diagnosis, and prevention of colon cancer.

HMGB3 is a Potential Therapeutic Target by Affecting the Migration and Proliferation of Colorectal Cancer

Colorectal cancer is one of the common malignant tumors in the digestive system, with high incidence and mortality rate. Therefore, there is an urgent need to identify and develop new molecular targets for colorectal cancer treatment. Previous studies have pointed out the important role of HMGB3 in tumors, and how it works in colorectal cancer needs to be studied in depth. In this study, we found that HMGB3 was highly expressed in COAD in the cBioPortal and GEPIA2 databases. Kaplan-Meier analysis showed that compared with patients with lower HMGB3 levels, patients with higher HMGB3 levels had poorer OS (p = 0.001). We also found a correlation between HMGB3 expression and immune infiltration of CRC. To investigate the mechanism of HMGB3 knockdown-mediated colorectal cancer inhibition, we detected a downregulation of N-cadherin, Vimentin and β-catenin proteins after knockdown of HMGB3. Taken together, HMGB3 can be an effective target for CRC treatment in the future, and we have reason to believe that HMGB3 will be of greater value in more tumors in the near future.

Pre-Administration of Berberine Exerts Chemopreventive Effects in AOM/DSS-Induced Colitis-Associated Carcinogenesis Mice via Modulating Inflammation and Intestinal Microbiota

Inflammatory activation and intestinal flora imbalance play an essential role in the development and progression of colorectal cancer (CRC). Berberine (BBR) has attracted great attention in recent years due to its heath-related benefits in inflammatory disorders and tumors, but the intricate mechanisms have not been fully elucidated. In this study, the effects and the mechanism of BBR on colon cancer were investigated in an azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced colitis-associated carcinogenesis mice model. Our results showed that pre-administration of BBR showed a decrease in weight loss, disease activity index (DAI) score, and the number of colon tumors in mice, compared with the model group. The evidence from pathological examination indicated that the malignancy of intestinal tumors was ameliorated after pre-administration of BBR. Additionally, pre-administration with BBR suppressed the expression of pro-inflammatory factors (interleukin (IL)-6, IL-1β, cyclooxygenase (COX)-2 and tumor necrosis factor (TNF)-α) and the cell-proliferation marker Ki67, while expression of the tight junction proteins (ZO-1 and occludin) were increased in colon tissue. Moreover, the levels of critical pathway proteins involved in the inflammatory process (p-STAT3 and p-JNK) and cell cycle regulation molecules (β-catenin, c-Myc and CylinD1) exhibited lower expression levels. Besides, 16S rRNA sequence analysis indicated that pre-administration of BBR increased the ratio of Firmicutes/Bacteroidetes (F:M) and the relative abundance of potentially beneficial bacteria, while the abundance of cancer-related bacteria was decreased. Gavage with Lactobacillus rhamnosus can improve the anti-tumor effect of BBR. Overall, pre-administration of BBR exerts preventive effects in colon carcinogenesis, and the mechanisms underlying these effects are correlated with the inhibition of inflammation and tumor proliferation and the maintenance of intestinal homeostasis.

The Association of Gut Microbiota and Complications in Gastrointestinal-Cancer Therapies

The therapy of gastrointestinal carcinomas includes surgery, chemo- or immunotherapy, and radiation with diverse complications such as surgical-site infection and enteritis. In recent years, the microbiome’s influence on different diseases and complications has been studied in more detail using methods such as next-generation sequencing. Due to the relatively simple collectivisation, the gut microbiome is the best-studied so far. While certain bacteria are sometimes associated with one particular complication, it is often just the loss of alpha diversity linked together. Among others, a strong influence of Fusobacterium nucleatum on the effectiveness of chemotherapies is demonstrated. External factors such as diet or specific medications can also predispose to dysbiosis and lead to complications. In addition, there are attempts to treat developed dysbiosis, such as faecal microbiota transplant or probiotics. In the future, the underlying microbiome should be investigated in more detail for a better understanding of the precipitating factors of a complication with specific therapeutic options.

Emerging Evidence of the Gut Microbiome in Chemotherapy: A Clinical Review

Increasing evidence suggests that the gut microbiome is associated with both cancer chemotherapy (CTX) outcomes and adverse events (AEs). This review examines the relationship between the gut microbiome and CTX as well as the impact of CTX on the gut microbiome. A literature search was conducted in electronic databases Medline, PubMed and ScienceDirect, with searches for "cancer" and "chemotherapy" and "microbiome/microbiota". The relevant literature was selected for use in this article. Seventeen studies were selected on participants with colorectal cancer (CRC; n=5), Acute Myeloid Leukemia (AML; n=3), Non-Hodgkin's lymphoma (n=2), breast cancer (BCa; n=1), lung cancer (n=1), ovarian cancer (n=1), liver cancer (n=1), and various other types of cancers (n=3). Seven studies assessed the relationship between the gut microbiome and CTX with faecal samples collected prior to (n=3) and following CTX (n=4) showing that the gut microbiome is associated with both CTX efficacy and toxicity. Ten other prospective studies assessed the impact of CTX during treatment and found that CTX modulates the gut microbiome of people with cancer and that dysbiosis induced by the CTX is related to AEs. CTX adversely impacts the gut microbiome, inducing dysbiosis and is associated with CTX outcomes and AEs. Current evidence provides insights into the gut microbiome for clinicians, cancer survivors and the general public. More research is required to better understand and modify the impact of CTX on the gut microbiome.

A Perspective on the Role of Microbiome for Colorectal Cancer Treatment

Simple Summary

Colorectal cancer is the third most diagnosed cancer worldwide and contributes significantly to global mortality and morbidity. The gut microbiome, composed of the trillions of microbes endemic to the human gastrointestinal tract, has been shown to be implicated in colorectal cancer oncogenesis; however, the roles of microbiota and dysbiosis in CRC treatment remain poorly understood. This review sought to characterize this relationship and in doing so, identify how these interactions may inform future treatments in the form of synbiotics designed to alter the host microbiota to achieve optimized treatment outcomes.

Abstract

In healthy hosts, trillions of microbes colonise the gut and oral cavity in a well-balanced state, maintaining a mutually beneficial relationship. Loss of this balance, termed dysbiosis, is strongly implicated in the pathogenesis of colorectal cancer (CRC). However, the roles of microbiota and dysbiosis in CRC treatment remain poorly understood. Recent studies suggest that the gut microbiota has the ability to affect the host response to chemotherapeutic agents by enhancing drug efficacy, promoting chemoresistance and mediating chemotherapy-induced toxicity and side effects via a variety of mechanisms. Several other studies have also proposed manipulation of the microbiota to optimise CRC treatment. In this review, we summarise the current advancement of knowledge on how microbiota and CRC treatments interact with each other and how this interaction may shed some light on the development of personalised microbiota manipulations that improve CRC treatment outcomes.

The Potential Role of the Intestinal Micromilieu and Individual Microbes in the Immunobiology of Chimeric Antigen Receptor T-Cell Therapy

Cellular immunotherapy with chimeric antigen receptor (CAR)-T cells (CARTs) represents a breakthrough in the treatment of hematologic malignancies. CARTs are genetically engineered hybrid receptors that combine antigen-specificity of monoclonal antibodies with T cell function to direct patient-derived T cells to kill malignant cells expressing the target (tumor) antigen. CARTs have been introduced into clinical medicine as CD19-targeted CARTs for refractory and relapsed B cell malignancies. Despite high initial response rates, current CART therapies are limited by a long-term loss of antitumor efficacy, the occurrence of toxicities, and the lack of biomarkers for predicting therapy and toxicity outcomes. In the past decade, the gut microbiome of mammals has been extensively studied and evidence is accumulating that human health, apart from our own genome, largely depends on microbes that are living in and on the human body. The microbiome encompasses more than 1000 bacterial species who collectively encode a metagenome that guides multifaceted, bidirectional host-microbiome interactions, primarily through the action of microbial metabolites. Increasing knowledge has been accumulated on the role of the gut microbiome in T cell-driven anticancer immunotherapy. It has been shown that antibiotics, dietary components and gut microbes reciprocally affect the efficacy and toxicity of allogeneic hematopoietic cell transplantation (allo HCT) as the prototype of T cell-based immunotherapy for hematologic malignancies, and that microbiome diversity metrics can predict clinical outcomes of allo HCTs. In this review, we will provide a comprehensive overview of the principles of CD19-CART immunotherapy and major aspects of the gut microbiome and its modulators that impact antitumor T cell transfer therapies. We will outline i) the extrinsic and intrinsic variables that can contribute to the complex interaction of the gut microbiome and host in CART immunotherapy, including ii) antibiotic administration affecting loss of colonization resistance, expansion of pathobionts and disturbed mucosal and immunological homeostasis, and ii) the role of specific gut commensals and their microbial virulence factors in host immunity and inflammation. Although the role of the gut microbiome in CART immunotherapy has only been marginally explored so far, this review may open a new chapter and views on putative connections and mechanisms.