Altered microbial bile acid metabolism exacerbates T cell-driven inflammation during graft-versus-host disease.

Microbial transformation of bile acids affects intestinal immune homoeostasis but its impact on inflammatory pathologies remains largely unknown. Using a mouse model of graft-versus-host disease (GVHD), we found that T cell-driven inflammation decreased the abundance of microbiome-encoded bile salt hydrolase (BSH) genes and reduced the levels of unconjugated and microbe-derived bile acids. Several microbe-derived bile acids attenuated farnesoid X receptor (FXR) activation, suggesting that loss of these metabolites during inflammation may increase FXR activity and exacerbate the course of disease. Indeed, mortality increased with pharmacological activation of FXR and decreased with its genetic ablation in donor T cells during mouse GVHD. Furthermore, patients with GVHD after allogeneic hematopoietic cell transplantation showed similar loss of BSH and the associated reduction in unconjugated and microbe-derived bile acids. In addition, the FXR antagonist ursodeoxycholic acid reduced the proliferation of human T cells and was associated with a lower risk of GVHD-related mortality in patients. We propose that dysbiosis and loss of microbe-derived bile acids during inflammation may be an important mechanism to amplify T cell-mediated diseases.

Immune-Related Colitis Is Associated with Fecal Microbial Dysbiosis and Can Be Mitigated by Fecal Microbiota Transplantation.

Colitis induced by treatment with immune-checkpoint inhibitors (ICI), termed irColitis, is a substantial cause of morbidity complicating cancer treatment. We hypothesized that abnormal fecal microbiome features would be present at the time of irColitis onset and that restoring the microbiome with fecal transplant from a healthy donor would mitigate disease severity. Herein, we present fecal microbiota profiles from 18 patients with irColitis from a single center, 5 of whom were treated with healthy-donor fecal microbial transplantation (FMT). Although fecal samples collected at onset of irColitis had comparable α-diversity to that of comparator groups with gastrointestinal symptoms, irColitis was characterized by fecal microbial dysbiosis. Abundances of Proteobacteria were associated with irColitis in multivariable analyses. Five patients with irColitis refractory to steroids and biologic anti-inflammatory agents received healthy-donor FMT, with initial clinical improvement in irColitis symptoms observed in four of five patients. Two subsequently exhibited recurrence of irColitis symptoms following courses of antibiotics. Both received a second "salvage" FMT that was, again, followed by clinical improvement of irColitis. In summary, we observed distinct microbial community changes that were present at the time of irColitis onset. FMT was followed by clinical improvements in several cases of steroid- and biologic-agent-refractory irColitis. Strategies to restore or prevent microbiome dysbiosis in the context of immunotherapy toxicities should be further explored in prospective clinical trials.

Learning from the microbes: exploiting the microbiome to enforce T cell immunotherapy.

The opportunities genetic engineering has created in the field of adoptive cellular therapy for cancer are accelerating the development of novel treatment strategies using chimeric antigen receptor (CAR) and T cell receptor (TCR) T cells. The great success in the context of hematologic malignancies has made especially CAR T cell therapy a promising approach capable of achieving long-lasting remission. However, the causalities involved in mediating resistance to treatment or relapse are still barely investigated. Research on T cell exhaustion and dysfunction has drawn attention to host-derived factors that define both the immune and tumor microenvironment (TME) crucially influencing efficacy and toxicity of cellular immunotherapy. The microbiome, as one of the most complex host factors, has become a central topic of investigations due to its ability to impact on health and disease. Recent findings support the hypothesis that commensal bacteria and particularly microbiota-derived metabolites educate and modulate host immunity and TME, thereby contributing to the response to cancer immunotherapy. Hence, the composition of microbial strains as well as their soluble messengers are considered to have predictive value regarding CAR T cell efficacy and toxicity. The diversity of mechanisms underlying both beneficial and detrimental effects of microbiota comprise various epigenetic, metabolic and signaling-related pathways that have the potential to be exploited for the improvement of CAR T cell function. In this review, we will discuss the recent findings in the field of microbiome-cancer interaction, especially with respect to new trajectories that commensal factors can offer to advance cellular immunotherapy.

Tissue-specific features of the T cell repertoire after allogeneic hematopoietic cell transplantation in human and mouse.

T cells are the central drivers of many inflammatory diseases, but the repertoire of tissue-resident T cells at sites of pathology in human organs remains poorly understood. We examined the site-specificity of T cell receptor (TCR) repertoires across tissues (5 to 18 tissues per patient) in prospectively collected autopsies of patients with and without graft-versus-host disease (GVHD), a potentially lethal tissue-targeting complication of allogeneic hematopoietic cell transplantation, and in mouse models of GVHD. Anatomic similarity between tissues was a key determinant of TCR repertoire composition within patients, independent of disease or transplant status. The T cells recovered from peripheral blood and spleens in patients and mice captured a limited portion of the TCR repertoire detected in tissues. Whereas few T cell clones were shared across patients, motif-based clustering revealed shared repertoire signatures across patients in a tissue-specific fashion. T cells at disease sites had a tissue-resident phenotype and were of donor origin based on single-cell chimerism analysis. These data demonstrate the complex composition of T cell populations that persist in human tissues at the end stage of an inflammatory disorder after lymphocyte-directed therapy. These findings also underscore the importance of studying T cell in tissues rather than blood for tissue-based pathologies and suggest the tissue-specific nature of both the endogenous and posttransplant T cell landscape.

Circulating microbial cell-free DNA is increased during neutropenia after hematopoietic stem cell transplantation.

We used a next-generation sequencing platform to characterize microbial cell-free DNA (mcfDNA) in plasma samples from patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HCT). In this observational study, we sought to characterize plasma mcfDNA in order to explore its potential association with the immunologic complications of transplantation. We compared serially collected patient samples with plasma collected from healthy control subjects. We observed changes in total mcfDNA burden in the plasma after transplantation, which was most striking during the early posttransplant neutropenic phase. This elevation could be attributed to a number of specific bacterial taxa, including Veillonella, Bacteroides, and Prevotella (genus level). For an additional cohort of patients, we compared the data of mcfDNA from plasma with 16s-ribosomal RNA sequencing data from stool samples collected at matched time points. In a number of patients, we confirmed that mcfDNA derived from specific microbial taxa (eg, Enterococcus) could also be observed in the matched stool sample. Quantification of mcfDNA may generate novel insights into mechanisms by which the intestinal microbiome influences systemic cell populations and, thus, has been associated with outcomes for patients with cancer.

High-resolution analyses of associations between medications, microbiome, and mortality in cancer patients.

Discerning the effect of pharmacological exposures on intestinal bacterial communities in cancer patients is challenging. Here, we deconvoluted the relationship between drug exposures and changes in microbial composition by developing and applying a new computational method, PARADIGM (parameters associated with dynamics of gut microbiota), to a large set of longitudinal fecal microbiome profiles with detailed medication-administration records from patients undergoing allogeneic hematopoietic cell transplantation. We observed that several non-antibiotic drugs, including laxatives, antiemetics, and opioids, are associated with increased Enterococcus relative abundance and decreased alpha diversity. Shotgun metagenomic sequencing further demonstrated subspecies competition, leading to increased dominant-strain genetic convergence during allo-HCT that is significantly associated with antibiotic exposures. We integrated drug-microbiome associations to predict clinical outcomes in two validation cohorts on the basis of drug exposures alone, suggesting that this approach can generate biologically and clinically relevant insights into how pharmacological exposures can perturb or preserve microbiota composition. The application of a computational method called PARADIGM to a large dataset of cancer patients' longitudinal fecal specimens and detailed daily medication records reveals associations between drug exposures and the intestinal microbiota that recapitulate in vitro findings and are also predictive of clinical outcomes.

A phase 2 study of interleukin-22 and systemic corticosteroids as initial treatment for acute GVHD of the lower GI tract.

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic transplantation. In experimental models, interleukin-22 promotes epithelial regeneration and induces innate antimicrobial molecules. We conducted a multicenter single-arm phase 2 study evaluating the safety and efficacy of a novel recombinant human interleukin-22 dimer, F-652, used in combination with systemic corticosteroids for treatment of newly diagnosed lower gastrointestinal acute GVHD. The most common adverse events were cytopenias and electrolyte abnormalities, and there were no dose-limiting toxicities. Out of 27 patients, 19 (70%; 80% confidence interval, 56%-79%) achieved a day-28 treatment response, meeting the prespecified primary endpoint. Responders exhibited a distinct fecal microbiota composition characterized by expansion of commensal anaerobes, which correlated with increased overall microbial α-diversity, suggesting improvement of GVHD-associated dysbiosis. This work demonstrates a potential approach for combining immunosuppression with tissue-supportive strategies to enhance recovery of damaged mucosa and promote microbial health in patients with gastrointestinal GVHD. This trial was registered at www.clinicaltrials.gov as NCT02406651.

Conditioning Regimens are Associated with Distinct Patterns of Microbiota Injury in Allogeneic Hematopoietic Cell Transplantation.

PURPOSE: The gut microbiota is subject to multiple insults in allogeneic hematopoietic cell transplantation (allo-HCT) recipients. We hypothesized that preparative conditioning regimens contribute to microbiota perturbation in allo-HCT. EXPERIMENTAL DESIGN: This was a retrospective study that evaluated the relationship between conditioning regimens exposure in 1,188 allo-HCT recipients and the gut microbiome. Stool samples collected from 20 days before transplantation up to 30 days after were profiled using 16S rRNA sequencing. Microbiota injury was quantified by changes in α-diversity. RESULTS: We identified distinct patterns of microbiota injury that varied by conditioning regimen. Diversity loss was graded into three levels of conditioning-associated microbiota injury (CMBI) in a multivariable model that included antibiotic exposures. High-intensity regimens, such as total body irradiation (TBI)-thiotepa-cyclophosphamide, were associated with the greatest injury (CMBI III). In contrast, the nonmyeloablative regimen fludarabine-cyclophosphamide with low-dose TBI (Flu/Cy/TBI200) had a low-grade injury (CMBI I). The risk of acute GVHD correlated with CMBI degree. Pretransplant microbial compositions were best preserved with Flu/Cy/TBI200, whereas other regimens were associated with loss of commensal bacteria and expansion of Enterococcus. CONCLUSIONS: Our findings support an interaction between conditioning at the regimen level and the extent of microbiota injury.

Preservation of the fecal microbiome is associated with reduced severity of graft-versus-host disease.

Following allogeneic hematopoietic cell transplantation (allo-HCT), the gastrointestinal (GI) tract is frequently affected by acute graft-versus-host disease (aGVHD), the pathophysiology of which is associated with a dysbiotic microbiome. Since microbial composition varies along the length of the GI tract, the authors hypothesized that microbiome features correlate with the pattern of organ involvement after allo-HCT. We evaluated 266 allo-HCT recipients from whom 1303 stool samples were profiled by 16S ribosomal gene sequencing. Patients were classified according to which organs were affected by aGVHD. In the 20 days prior to disease onset, GVHD patients had lower abundances of members of the class Clostridia, lower counts of butyrate producers, and lower ratios of strict-to-facultative (S/F) anaerobic bacteria compared with allograft recipients who were free of GVHD. GI GVHD patients showed significant reduction in microbial diversity preonset. Patients with lower GI aGVHD had lower S/F anaerobe ratios compared with those with isolated upper GI aGVHD. In the 20 days after disease onset, dysbiosis was observed only in GVHD patients with GI involvement, particularly those with lower-tract disease. Importantly, Clostridial and butyrate-producer abundance as well as S/F anaerobe ratio were predictors of longer overall survival; higher abundance of butyrate producers and higher S/F anaerobe ratio were associated with decreased risk of GVHD-related death. These findings suggest that the intestinal microbiome can serve as a biomarker for outcomes of allo-HCT patients with GVHD.

A prospective study of dysgeusia and related symptoms in patients with multiple myeloma after autologous hematopoietic cell transplantation.

BACKGROUND: Dysgeusia is a common but understudied complication in patients undergoing autologous hematopoietic cell transplantation (auto-HCT). We assessed the feasibility of using chemical gustometry (CG) to measure dysgeusia and explored its associations with symptom burden, nutrition, chemotherapy pharmacokinetics (PK), and the oral microbiome. METHODS: We conducted a single-center, prospective feasibility study (NCT03276481) of patients with multiple myeloma undergoing auto-HCT. CG was performed longitudinally testing five flavors (sweet, sour, salty, bitter, umami) to calculate a total taste score (maximum score, 30). We measured caloric intake and patient-reported symptoms, assessing their correlation with oral microbiota composition and salivary and blood melphalan PK exposure. RESULTS: Among all 45 patients, 39 (87%) completed at least four (>60%) and 22 (49%) completed all six CG assessments. Median total CG scores remained stable over time but were lowest at day +7 (27, range 24-30) with recovery by day +100. Symptom burden was highest by day +10 (area under the curve, 2.9; range, 1.0-4.6) corresponding with the lowest median overall caloric intake (1624 kcal; range, 1345-2267). Higher serum/salivary melphalan levels correlated with higher patient-reported dysgeusia and lower caloric intake. Oral microbiota α-diversity was stable early and increased slightly by day +100. CONCLUSIONS: Assessment of dysgeusia by CG is feasible after auto-HCT. Most dysgeusia, symptom burden, and lowest caloric intake occurred during the blood count nadir. Higher melphalan concentrations correlated with more dysgeusia and poorer caloric intake. Future studies will aim to modulate melphalan exposure by PK-targeted dosing and characterize patient taste preferences to personalize diets for improved nutritional intake. LAY SUMMARY: Taste changes after cancer treatments are very common. We used chemical gustometry (taste testing) to study taste changes and to better understand why patients with multiple myeloma experience this symptom after autologous hematopoietic cell transplantation. We found that taste testing was feasible, taste changes peaked when blood counts were lowest, and most patients recovered their taste by 100 days after transplantation. Taste changes correlated with lower food intake and with higher levels of chemotherapy in the body. Future work will focus on using personalized chemotherapy doses to reduce taste changes and to match patients' individual taste preferences with their diets.

Vitamin D Insufficiency and Clinical Outcomes with Chimeric Antigen Receptor T-Cell Therapy in Large B-cell Lymphoma.

Vitamin D insufficiency is a potentially modifiable risk factor for poor outcomes in newly diagnosed large B-cell lymphoma (LBCL). However, the role of circulating vitamin D concentrations in relapsed/refractory LBCL treated with CD19-directed chimeric antigen receptor T-cell therapy (CAR-T) is currently unknown. This was a single-center, observational study that evaluated the association of pre-CAR-T 25-hydroxyvitamin D (25-OHD) status with 100-day complete response, progression-free survival, overall survival, and CAR-T-related toxicity in 111 adult relapsed/refractory LBCL patients. Vitamin D insufficiency was defined as ≤30 ng/mL in accordance with the Endocrine Society guidelines. The median pre-CAR-T 25-hydroxyvitamin D concentration was 24 ng/mL (interquarile range = 18-34). Vitamin D-insufficient patients (≤30 ng/mL; n = 73 [66%]) were significantly younger than their vitamin D-replete (>30 ng/mL; n = 38 [34%]) counterparts (P= .039). The vitamin D-insufficient cohort was enriched for de novo LBCL as the histological subtype (P= .026) and had a higher proportion of tisagenlecleucel as the CAR-T product (P= .049). There were no other significant differences in the baseline characteristics between the two groups. In vitamin D-insufficient compared to -replete patients, 100-day complete response was 55% versus 76% (P= .029), and 2-year overall survival was 41% versus 71% (P= .061), respectively. In multivariate analysis, vitamin D insufficiency remained significantly associated with 100-day complete response (odds ratio 2.58 [1.05-6.83]; P= .045) and overall survival (hazard ratio 2.24 [1.08-4.66], P= .030). In recipients of tisagenlecleucel, vitamin D insufficiency was associated with significantly lower cell viability of the infused CAR-T product (P= .015). Finally, pretreatment vitamin D insufficiency did not predict for subsequent CAR-T-related toxicity. This is the first report to demonstrate that vitamin D insufficiency is associated with inferior clinical outcomes in CAR-T recipients. Further study into the mechanistic insights of this finding, and the potential role of vitamin D supplementation to optimize CAR-T are warranted.

MAIT and Vδ2 unconventional T cells are supported by a diverse intestinal microbiome and correlate with favorable patient outcome after allogeneic HCT.

Microbial diversity is associated with improved outcomes in recipients of allogeneic hematopoietic cell transplantation (allo-HCT), but the mechanism underlying this observation is unclear. In a cohort of 174 patients who underwent allo-HCT, we demonstrate that a diverse intestinal microbiome early after allo-HCT is associated with an increased number of innate-like mucosal-associated invariant T (MAIT) cells, which are in turn associated with improved overall survival and less acute graft-versus-host disease (aGVHD). Immune profiling of conventional and unconventional immune cell subsets revealed that the prevalence of Vδ2 cells, the major circulating subpopulation of γδ T cells, closely correlated with the frequency of MAIT cells and was associated with less aGVHD. Analysis of these populations using both single-cell transcriptomics and flow cytometry suggested a shift toward activated phenotypes and a gain of cytotoxic and effector functions after transplantation. A diverse intestinal microbiome with the capacity to produce activating ligands for MAIT and Vδ2 cells appeared to be necessary for the maintenance of these populations after allo-HCT. These data suggest an immunological link between intestinal microbial diversity, microbe-derived ligands, and maintenance of unconventional T cells.

Gut microbiome correlates of response and toxicity following anti-CD19 CAR T cell therapy.

Anti-CD19 chimeric antigen receptor (CAR) T cell therapy has led to unprecedented responses in patients with high-risk hematologic malignancies. However, up to 60% of patients still experience disease relapse and up to 80% of patients experience CAR-mediated toxicities, such as cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. We investigated the role of the intestinal microbiome on these outcomes in a multicenter study of patients with B cell lymphoma and leukemia. We found in a retrospective cohort (n = 228) that exposure to antibiotics, in particular piperacillin/tazobactam, meropenem and imipenem/cilastatin (P-I-M), in the 4 weeks before therapy was associated with worse survival and increased neurotoxicity. In stool samples from a prospective cohort of CAR T cell recipients (n = 48), the fecal microbiome was altered at baseline compared to healthy controls. Stool sample profiling by 16S ribosomal RNA and metagenomic shotgun sequencing revealed that clinical outcomes were associated with differences in specific bacterial taxa and metabolic pathways. Through both untargeted and hypothesis-driven analysis of 16S sequencing data, we identified species within the class Clostridia that were associated with day 100 complete response. We concluded that changes in the intestinal microbiome are associated with clinical outcomes after anti-CD19 CAR T cell therapy in patients with B cell malignancies.

Early intestinal microbial features are associated with CD4 T-cell recovery after allogeneic hematopoietic transplant.

Low intestinal microbial diversity is associated with poor outcomes after allogeneic hematopoietic cell transplantation (HCT). Using 16S rRNA sequencing of 2067 stool samples and flow cytometry data from 2370 peripheral blood samples drawn from 894 patients who underwent allogeneic HCT, we have linked features of the early post-HCT microbiome with subsequent immune cell recovery. We examined lymphocyte recovery and microbiota features in recipients of both unmodified and CD34-selected allografts. We observed that fecal microbial diversity was an independent predictor of CD4 T-cell count 3 months after HCT in recipients of a CD34-selected allograft, who are dependent on de novo lymphopoiesis for their immune recovery. In multivariate models using clinical factors and microbiota features, we consistently observed that increased fecal relative abundance of genus Staphylococcus during the early posttransplant period was associated with worse CD4 T-cell recovery. Our observations suggest that the intestinal bacteria, or the factors they produce, can affect early lymphopoiesis and the homeostasis of allograft-derived T cells after transplantation.

Fecal microbiota diversity disruption and clinical outcomes after auto-HCT: a multicenter observational study.

We previously described clinically relevant reductions in fecal microbiota diversity in patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT). Recipients of high-dose chemotherapy and autologous HCT (auto-HCT) incur similar antibiotic exposures and nutritional alterations. To characterize the fecal microbiota in the auto-HCT population, we analyzed 1161 fecal samples collected from 534 adult recipients of auto-HCT for lymphoma, myeloma, and amyloidosis in an observational study conducted at 2 transplantation centers in the United States. By using 16S ribosomal gene sequencing, we assessed fecal microbiota composition and diversity, as measured by the inverse Simpson index. At both centers, the diversity of early pretransplant fecal microbiota was lower in patients than in healthy controls and decreased further during the course of transplantation. Loss of diversity and domination by specific bacterial taxa occurred during auto-HCT in patterns similar to those with allo-HCT. Above-median fecal intestinal diversity in the periengraftment period was associated with decreased risk of death or progression (progression-free survival hazard ratio, 0.46; 95% confidence interval, 0.26-0.82; P = .008), adjusting for disease and disease status. This suggests that further investigation into the health of the intestinal microbiota in auto-HCT patients and posttransplant outcomes should be undertaken.

The microbe-derived short-chain fatty acids butyrate and propionate are associated with protection from chronic GVHD.

Studies of the relationship between the gastrointestinal microbiota and outcomes in allogeneic hematopoietic stem cell transplantation (allo-HCT) have thus far largely focused on early complications, predominantly infection and acute graft-versus-host disease (GVHD). We examined the potential relationship of the microbiome with chronic GVHD (cGVHD) by analyzing stool and plasma samples collected late after allo-HCT using a case-control study design. We found lower circulating concentrations of the microbe-derived short-chain fatty acids (SCFAs) propionate and butyrate in day 100 plasma samples from patients who developed cGVHD, compared with those who remained free of this complication, in the initial case-control cohort of transplant patients and in a further cross-sectional cohort from an independent transplant center. An additional cross-sectional patient cohort from a third transplant center was analyzed; however, serum (rather than plasma) was available, and the differences in SCFAs observed in the plasma samples were not recapitulated. In sum, our findings from the primary case-control cohort and 1 of 2 cross-sectional cohorts explored suggest that the gastrointestinal microbiome may exert immunomodulatory effects in allo-HCT patients at least in part due to control of systemic concentrations of microbe-derived SCFAs.

Microbiota as Predictor of Mortality in Allogeneic Hematopoietic-Cell Transplantation.

BACKGROUND: Relationships between microbiota composition and clinical outcomes after allogeneic hematopoietic-cell transplantation have been described in single-center studies. Geographic variations in the composition of human microbial communities and differences in clinical practices across institutions raise the question of whether these associations are generalizable. METHODS: The microbiota composition of fecal samples obtained from patients who were undergoing allogeneic hematopoietic-cell transplantation at four centers was profiled by means of 16S ribosomal RNA gene sequencing. In an observational study, we examined associations between microbiota diversity and mortality using Cox proportional-hazards analysis. For stratification of the cohorts into higher- and lower-diversity groups, the median diversity value that was observed at the study center in New York was used. In the analysis of independent cohorts, the New York center was cohort 1, and three centers in Germany, Japan, and North Carolina composed cohort 2. Cohort 1 and subgroups within it were analyzed for additional outcomes, including transplantation-related death. RESULTS: We profiled 8767 fecal samples obtained from 1362 patients undergoing allogeneic hematopoietic-cell transplantation at the four centers. We observed patterns of microbiota disruption characterized by loss of diversity and domination by single taxa. Higher diversity of intestinal microbiota was associated with a lower risk of death in independent cohorts (cohort 1: 104 deaths among 354 patients in the higher-diversity group vs. 136 deaths among 350 patients in the lower-diversity group; adjusted hazard ratio, 0.71; 95% confidence interval [CI], 0.55 to 0.92; cohort 2: 18 deaths among 87 patients in the higher-diversity group vs. 35 deaths among 92 patients in the lower-diversity group; adjusted hazard ratio, 0.49; 95% CI, 0.27 to 0.90). Subgroup analyses identified an association between lower intestinal diversity and higher risks of transplantation-related death and death attributable to graft-versus-host disease. Baseline samples obtained before transplantation already showed evidence of microbiome disruption, and lower diversity before transplantation was associated with poor survival. CONCLUSIONS: Patterns of microbiota disruption during allogeneic hematopoietic-cell transplantation were similar across transplantation centers and geographic locations; patterns were characterized by loss of diversity and domination by single taxa. Higher diversity of intestinal microbiota at the time of neutrophil engraftment was associated with lower mortality. (Funded by the National Cancer Institute and others.).

Minimal residual disease negativity in multiple myeloma is associated with intestinal microbiota composition.

Patients with multiple myeloma (MM) who achieve minimal residual disease (MRD) negativity after upfront treatment have superior outcomes compared with those who remain MRD+ Recently, associations have been shown between specific commensal microbes and development of plasma cell disorders. Here, we report the association between intestinal microbiota composition and treatment outcome in MM. Microbiota composition of fecal samples collected from 34 MM patients after induction therapy and at the time of flow cytometry-based bone marrow MRD testing was determined by 16S ribosomal RNA sequencing. We observed a higher relative abundance of Eubacterium hallii in the 16 MRD- patients relative to the 18 MRD+ patients. No association was observed between microbial relative abundance and autologous stem cell transplantation history or MM paraprotein isotype. No differences in microbiota α diversity were observed between MRD- and MRD+ patients. The potential association of microbiota composition with treatment response in MM patients is an important parameter for additional correlative and clinical investigation.

Intestinal Microbiota and Relapse After Hematopoietic-Cell Transplantation.

Purpose The major causes of mortality after allogeneic hematopoietic-cell transplantation (allo-HCT) are relapse, graft-versus-host disease (GVHD), and infection. We have reported previously that alterations in the intestinal flora are associated with GVHD, bacteremia, and reduced overall survival after allo-HCT. Because intestinal bacteria are potent modulators of systemic immune responses, including antitumor effects, we hypothesized that components of the intestinal flora could be associated with relapse after allo-HCT. Methods The intestinal microbiota of 541 patients admitted for allo-HCT was profiled by means of 16S ribosomal sequencing of prospectively collected stool samples. We examined the relationship between abundance of microbiota species or groups of related species and relapse/progression of disease during 2 years of follow-up time after allo-HCT by using cause-specific proportional hazards in a retrospective discovery-validation cohort study. Results Higher abundance of a bacterial group composed mostly of Eubacterium limosum in the validation set was associated with a decreased risk of relapse/progression of disease (hazard ratio [HR], 0.82 per 10-fold increase in abundance; 95% CI, 0.71 to 0.95; P = .009). When the patients were categorized according to presence or absence of this bacterial group, presence also was associated with less relapse/progression of disease (HR, 0.52; 95% CI, 0.31 to 0.87; P = .01). The 2-year cumulative incidences of relapse/progression among patients with and without this group of bacteria were 19.8% and 33.8%, respectively. These associations remained significant in multivariable models and were strongest among recipients of T-cell-replete allografts. Conclusion We found associations between the abundance of a group of bacteria in the intestinal flora and relapse/progression of disease after allo-HCT. These might serve as potential biomarkers or therapeutic targets to prevent relapse and improve survival after allo-HCT.