van den Brink, Marcel R M

Abstract Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for many hematological malignancies, but graft-versus-host disease (GVHD) is a common complication. Low gut microbiome diversity is associated with higher GVHD risk and shorter survival in multiple studies. Recently, the BMT CTN 1703 clinical trial demonstrated superiority of a GVHD-prophylaxis regimen including post-transplant cyclophosphamide (PTCy) compared to the standard prophylaxis (tacrolimus and methotrexate, Tac/MTX) in terms of GVHD-free, relapse-free survival at one year among reduced intensity conditioning allo-HCT recipients. However, the effect of PTCy on the gut microbiome and its association with clinical outcome have not been described. Here, we report on a companion randomized clinical controlled trial (BMT CTN 1801), which collected 2575 longitudinal stool samples from 304 study participants. Samples were obtained up to weekly up to day 84 post allo-HCT and at less frequent intervals thereafter, up to 2 years. Microbiome diversity and absolute microbial load were lower in the PTCy group compared to the Tac/MTX group on days 14–28 post-HCT. However, diversity at the timepoint closest to neutrophil engraftment was not significantly associated with non-relapse mortality after one year or other clinical outcomes, contrary to expectations from previous studies. Microbial domination events, when a single species exceeds 30% relative abundance, were comparable across treatment arms and reflected both pathogen blooms as well as less severe disruptions of the microbial community. Clostridium scindens and secondary bile acid metabolism pathways were less prevalent in the PTCy arm than in the Tac/MTX arm post-HCT, yet presence of secondary bile acid metabolism pathways was associated with a lower risk of chronic GVHD. Given that PTCy was associated with a greater disruption of the microbiome as measured by diversity, absolute microbial abundance, and bile acid metabolism capability, but better clinical outcomes overall, these data suggest that the importance of the microbiome in modulating the host immune systems after allo-HCT is specific to different types of GVHD prophylaxis.

Abstract Consumption of a Western diet and high body mass index (BMI) are risk factors for progression from premalignant phenotypes to multiple myeloma, a hematologic cancer. In the NUTRIVENTION trial (NCT04920084), we administered a high-fiber, plant-based diet (HFPBD; meals for 12 weeks, coaching for 24 weeks) to 23 participants with myeloma precursor states and elevated BMI. The intervention was feasible and improved quality of life and modifiable risk factors: metabolic (BMI, insulin resistance), microbiome (diversity, composition), and immune (inflammation, monocyte subsets). Disease progression trajectory improved (n = 2) or was stable. Findings were translated to Vk*MYC mice modeling the myeloma precursor state, in which a high-fiber diet (HFD) delayed disease progression through improved metabolism and microbiome composition, leading to increased short-chain fatty acid production that reinvigorated antitumor immunity and inhibited tumor growth. These effects from fiber consumption were independent of calorie restriction and weight loss. A HFD is a low-risk intervention that may delay progression to myeloma. Significance: A HFPBD in participants with precursor plasma cell disorders and an elevated BMI improved metabolic, microbiome, and immune biomarkers of disease. In a subset, it may delay progression to myeloma. In mouse models, a HFD delayed progression to myeloma independent of calorie restriction. See related commentary by Fairfield and Reagan, p. 623

6554 Background: SER-155 is an investigational, oral, live biotherapeutic product (LBP) comprised of 16 bacterial strains designed to decolonize gastrointestinal (GI) pathogens, improve epithelial barrier integrity, and modulate immune responses to prevent bloodstream infections (BSI). In the placebo-controlled cohort 2 of the phase 1b study, SER-155-001 (NCT04995653), SER-155 was generally well tolerated with a safety profile similar to placebo and the incidence of BSIs, a secondary endpoint, was significantly lower after treatment with SER-155 when compared to placebo. We report exploratory analyses of biomarkers of T cell expansion relevant for immune reconstitution after HCT. Methods: Participants were randomized 1:1 to receive 4 days of oral vancomycin (for microbiome conditioning) and 10 days of SER-155 or placebo/placebo administered pre-HCT (course 1) and post-neutrophil engraftment (course 2). Primary endpoints were safety and SER-155 strain engraftment (PK). Exploratory endpoints included plasma cytokine concentrations measured by ELISA and analysis of peripheral blood mononuclear cells (PBMCs) by flow cytometry. Results: Demographics were comparable across treatment arms. 34 of 45 randomized participants were treated and received allo-HCT (SER-155, 20; placebo, 14); 28 received course 2 (SER-155, 19; placebo, 9). SER-155 strain engraftment was observed in the peri-transplant period (median 11.5 strains after course 1) and post-HCT (median 11 strains after course 2 and HCT Day 100). Significant differences and trends in cytokines of systemic inflammation and immune homeostasis were observed relative to placebo prior to HCT Day 0 and post-HCT. On HCT Day 0, both arms had similar concentrations of IL7 and IL15 (Table 1). However, after course 2, and at HCT Day 100, significantly higher concentrations of IL7 were observed in the SER-155 arm relative to placebo (p=0.02, and p=0.003, respectively). In a preliminary analysis of PBMCs from a subset of participants, a high frequency of CD4+ T cells were observed in the SER-155 arm at the same timepoints. For homeostatic cytokine IL15, no significant differences were observed between arms. Conclusions: The significantly higher concentrations of IL7 with SER-155 treatment and observed frequency of CD4+ T cells support the potential role of the GI microbiome in promoting homeostatic expansion of peripheral T cells and immune reconstitution important for successful HCT. Clinical trial information: NCT04995653 . Median plasma IL7 and IL15 (pg/mL), SER-155 vs. placebo (generalized linear model). HCT Day or event SER-155 IL7 Placebo IL7 SER-155 IL15 Placebo IL15 D0 13.8 13.0 31.9 30.4 D7 15.1 14.6 50.9 62.6 D14 12.8 15.5 56.6 69.8 Post-neutrophil engraftment 13.4 9.0 16.3 15.4 Post-course 2 7.4* 3.9 6.2 9.1 D100 7.1** 3.5 6.2 6.2 *p<0.05, **p<0.01.

Introduction Poor diet quality, elevated body mass index (BMI), insulin resistance, microbiome dysbiosis, inflammation as well as immune dysfunction have all been implicated in progression from monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM) to multiple myeloma (MM). Plant-based diets have been associated with reduced risk of MGUS and MM in epidemiological studies. Whether a dietary intervention can impact these modifiable risk factors and delay disease progression has not been investigated. Methods We conducted a pilot, single-arm trial providing controlled high fiber plant based dietary (HFPBD) intervention for 12 weeks and health coaching for 24 weeks in 20 patients with MGUS/SMM with BMI≥25 (NCT04920084). The primary endpoint was feasibility (adherence and BMI reduction). Secondary and exploratory endpoints included quality of life, metabolic markers (insulin, adiponectin, leptin, LDL cholesterol), microbiome (diversity and composition by 16S and shotgun sequencing) and immune profiling in peripheral blood (flow cytometry and Olink inflammation panel) and bone marrow (scRNAseq and ATACseq). We also conducted an in vivo study in transgenic Vk*MYC mice fed a high fiber or control diet at the phase of mouse(m)SMM. The mice were monitored for the progression to active mMM. Differences in microbiome and immune response profiles between high fiber- and control-treated mice were assessed via microbiome 16S sequencing and flow cytometry. Results The HFPBD intervention was safe, feasible, improved quality of life and addressed modifiable risk factors - metabolic profile (improved BMI, insulin resistance, adiponectin leptin ratio), microbiome profile (increased alpha-diversity and butyrate producers) and immune (decreased inflammation and increased anti-inflammatory classical monocyte) subsets. A reduction in long-term progression trajectory was observed in 2 patients. Consistently, the high fiber diet delayed progression from mSMM to mMM in Vk*MYC mice increasing median progression-free survival from 12 weeks in the control arm to 30 weeks in the high fiber diet intervention arm. Additionally, in the intervention arm 40% of mice did not progress to mMM during the study period whereas all mice in the control arm progressed. Both human and mouse data showed that HFPBD modulated gut microbiota composition favoring the expansion of butyrate-producing bacteria. Additionally, short-chain fatty acids were increased in the feces of mice fed a high fiber diet. Integrated analysis from human bone marrow and peripheral blood analysis indicated that the dietary intervention reduced inflammatory biomarkers and skewed the immune response towards T helper and CD14+ monocytes. Consistently, the bone marrow of Vk*MYC mice fed high fiber diet was more infiltrated by IFNg-producing T lymphocytes while displaying less exhausted T cells and immunosuppressive myeloid cells. Conclusion This is the first interventional clinical trial and in vivo study to show that a HFPBD intervention may delay progression from MGUS/SMM to MM. To our knowledge there has been no similar dietary interventional study in hematological cancers or solid tumors. Together our in vivo and clinical data support the beneficial anti-inflammatory role of a HFPBD providing a link between diet, microbiota, and immune modulation to delay disease progression in MGUS/SMM.

6554 Background: Acute graft- versus-host disease (aGvHD) is a life-threatening complication following allo-HCT. Microbiome dysfunction and associated GI barrier disruption may contribute to aGvHD via activation of inflammatory immune responses. Circulating biomarkers in the peri-transplant period are correlated with risk of severe aGvHD, including suppression of tumorigenicity 2 (ST2), regenerating islet-derived 3-alpha (Reg3a) and inflammatory cytokines (IL6, IFNϒγ & TNFα). SER-155 is an investigational cultivated oral microbiome therapeutic designed to restructure the GI microbiome, improve GI barrier integrity and reduce GI inflammation and is being assessed in a 2-part Phase 1b study in adults undergoing allo-HCT. We present preliminary safety, GvHD, PK, and exploratory biomarker data from the completed open-label Cohort 1 through Day 100 post-HCT. Methods: Adult recipients of allo-HCT were eligible. HCT conditioning and aGvHD prophylaxis were per investigator discretion. Patients received 2 courses of SER-155 (pre-HCT and post-neutrophil engraftment, each comprised of 4 days of microbiome conditioning with oral vancomycin followed by 10 days oral SER-155. The primary endpoint was safety. Strain engraftment (PK) and biomarkers were assessed in stool and plasma samples. Results: Fifteen adults enrolled; 13 received at least 1 course of study drug (median age 67; 54% male), and 11 underwent allo-HCT. Following each course, the majority of the 16 SER-155 strains were detected in stool. Treatment-emergent adverse events (AEs) were reported in all patients with GI AEs the most common. No serious AEs (SAEs) were deemed related to SER-155. Most SAEs and AEs of special interest (ie, BSIs, invasive or GI infections) occurred between HCT and the 2nd SER-155 course. There were no deaths before Day 100. No BSIs were attributable to SER-155 strains. The rate of grade 2-4 aGvHD based on MAGIC criteria through Day 100 was 45.5%; no severe grade 3-4 aGvHD was observed. Median levels of plasma biomarkers REG3α, ST2 and inflammatory cytokines were not elevated relative to a reference range (Table). Conclusions: In this small open-label cohort, SER-155 was generally well-tolerated through Day 100 without drug-related SAEs and no severe aGvHD. Plasma biomarkers were not elevated at HCT Day 0 or neutrophil recovery. These preliminary observations align with the design and preclinical evaluation of SER-155. Clinical trial information: NCT04995653 . [Table: see text]

Background: In patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT), low gastrointestinal (GI) microbial diversity is associated with risk of bloodstream infections (BSIs), acute graft-versus-host disease (aGvHD), and death. SER-155 is an investigational cultivated microbiome therapeutic rationally designed to improve clinical outcomes in allo-HCT patients by preventing pathogen domination, promoting epithelial barrier integrity, and reducing colonic inflammation. SER-155-001 is a 2-part, Phase 1b study evaluating the safety, tolerability, pharmacokinetics, and efficacy of SER-155 in adults undergoing allo-HCT. Here, we present preliminary safety and tolerability data from the open-label Cohort 1 through Day 100 post HCT. Study Design and Methods: Adult recipients of allo-HCT were eligible for screening. Patients were excluded if they: a) were planned for umbilical cord blood or ex vivo T-cell depletion, b) had received a fecal microbiota transplant or any live biotherapeutic product within 3 months prior to screening, and/or c) had evidence of relapse or progression of hematologic malignancy (minimal residual disease was allowed). HCT conditioning and aGvHD prophylaxis were per investigator discretion. Following screening, patients received two treatment courses (before conditioning and after neutrophil engraftment) comprised of microbiome conditioning with 4 days of oral vancomycin (to facilitate engraftment of SER-155 strains) followed by 10 days of oral SER-155 (see study design schematic, Figure 1). The primary endpoint was the incidence and severity of adverse events (AEs), serious adverse events (SAEs), and adverse events of special interest (AESIs), designated as invasive infection, BSI, and GI infection. Results: Fifteen adult patients were enrolled and 13 received study drug (safety population). Of these 13 patients, the median age was 67.0, all were White, and 54% were male. Underlying diseases included acute myeloid leukemia (6 patients [46.2%]); myelodysplastic syndromes and myeloproliferative neoplasms (2 patients each [15.4%]; and acute lymphoblastic leukemia, chronic myeloid leukemia, and classic Hodgkin's lymphoma (1 patient each [7.7%]). Ten patients (76.9%) received peripheral blood stem cells; 9 (69.2%) had an unrelated donor, 8 (61.5%) underwent a reduced-intensity conditioning regimen, and 3 (23.1%) received myeloablative conditioning. Eleven patients received allo-HCT, all patients had neutrophil engraftment within the expected timeframe and 10 had 100-day follow-up data available. Nine of these patients (81.8%) received tacrolimus/methotrexate-based GvHD prophylaxis. SER-155 was generally well-tolerated ( Table 1). Treatment-emergent AEs (TEAEs) were observed in all patients as is expected in this patient population. One TEAE considered unrelated to study drug, resulted in study discontinuation. Most AEs were gastrointestinal in nature with diarrhea being the most common AE. No SAEs were considered related to SER 155, and most SAEs and AESIs occurred after HCT and before starting the second course of SER-155. No deaths occurred prior to Day 100. Three deaths occurred after Day 100, all deemed to be unrelated to study drug by the investigators. No BSIs attributable to organisms in SER-155 occurred. Commencement of the double-blind, randomized, placebo-controlled Cohort 2 (n=60) was initiated following approval of the Data Safety Monitoring Committee. Conclusions: In patients enrolled in this open-label Cohort 1 of this Phase 1b study, SER-155 was well-tolerated through Day 100. Although sample size is limited, the observed safety and tolerability profile of SER-155 in this patient population is consistent with multiple preclinical assessments supporting the safety of SER-155 for therapeutic use. Enrollment in the double-blind, randomized, placebo-controlled second cohort to assess safety, efficacy, and changes in microbiome composition and function is ongoing.

Introduction: During allogeneic hematopoietic cell transplantation (allo-HCT), conditioning regimens disrupt the epithelial barrier of the gastrointestinal (GI) tract and broad-spectrum antibiotics cause microbiome disruption characterized by low microbial diversity and high abundance of pathogens that can dominate gut communities. Microbiome disruption is associated with increased translocation of pathogenic bacteria leading to risk of bloodstream infections (BSIs) and acute graft-vs-host disease (aGvHD). Nonclinical studies have demonstrated that domination with pathogens leads to immune activation and subsequent GvHD following exposure to bacterial antigens in the gut-associated lymphoid tissue [ Jenq 2015 Biol Blood Marrow Transplant, Stein-Thoeringer 2019 Science, Peled 2020 NEJM]. SER-155, an oral investigational cultivated microbiome therapeutic comprised of 16 bacterial Firmicutes strains, was designed to engraft in the GI tract, improve GI barrier integrity, and restructure the GI microbiome by introducing bacteria with immunomodulatory and anti-inflammatory properties and driving a reduction in abundance of proinflammatory bacteria [ Halvorsen 2021 OFID, 2022 Bone Marrow Transplant]. Herein, we present preliminary clinical data through Day 100 from an open-label cohort of a Phase 1b study in patients undergoing allo-HCT (NCT04995653) and compare the incidence of GI pathogen domination in this cohort to a historical cohort. Methods: Study patients received two treatment courses of SER-155 (before conditioning and after neutrophil engraftment), each comprised of microbiome conditioning with 4 days oral vancomycin (to facilitate engraftment of SER-155 strains into the GI microbiome) followed by 10 days of oral SER-155. The primary endpoint was safety. Stool samples collected pre- and post-HCT were used to evaluate secondary endpoints, including engraftment of SER-155 strains (following each course of SER-155) and GI pathogen domination, defined as a relative abundance of a specific taxa at ≥30% ( Peled, 2020). Engraftment of SER-155 strains was assessed via strain-specific molecular probes (NanoString). Relative abundance of Enterobacteriaceae, Enterococcaceae, Streptococcaceae and Staphylococcaceae was assessed with whole metagenomic shotgun sequencing (WMS). A post-hoc comparison of GI domination was made with a historical cohort of 459 HCT patients with similar patient characteristics from one of the study sites (MSKCC) using stool samples profiled by 16S-amplicon sequencing. Results: Fifteen adults (median age 67 years; 54% male) were enrolled and 13 received study drug. SER-155 was generally well-tolerated. Following each course of SER-155, the majority of the 16 strains in SER-155 were detected in evaluable patients (median = 11 strains in 8 patients before conditioning; median = 12 strains in 7 patients after neutrophil engraftment).Between the day of transplant (Day 0) and Day 30, GI domination with potentially pathogenic bacteria occurred in only 1 of 9 (11%) evaluable patients (Figure 1). In contrast, in the historical comparator cohort, 64% of patients (294 of 459) had pathogen domination during the same timeframe, with domination by Enterococcus being most common. Conclusions: The observation of SER-155 strain engraftment before transplant and low incidence of GI pathogen domination after transplant through Day 30 are encouraging, although these preliminary data are limited by the small size of this open-label cohort of HCT patients. These observations are consistent with the design and preclinical evaluation of SER-155, supporting further development of this investigational cultivated microbiome therapeutic. Enrollment in the second double-blind, randomized, placebo-controlled cohort (approximately 60 participants) has initiated following a preplanned review by the Data Safety Monitoring Committee.

TPS7080 Background: In patients undergoing allogeneic hematopoietic cell transplantation (HCT), loss of gastrointestinal microbial diversity is associated with risk of bloodstream infections (BSI), acute graft-versus-host disease (aGvHD), and death. SER-155 is a rationally designed investigational cultivated microbiome therapeutic, hypothesized to improve clinical outcomes in HCT by restoring colonization resistance to potential pathogens, promoting epithelial barrier integrity, and reducing colonic inflammation. SER-155-001 is a Phase 1b study evaluating the efficacy, safety, and pharmacokinetics (PK) of SER-155 in adults undergoing HCT. Methods: This study will enroll approximately 70 subjects ≥18 years in an open-label Cohort 1 (n = 10) followed by a double-blind, placebo-controlled Cohort 2 (n = 60) randomized 1:1 to SER-155 or placebo. A variety of conditioning regimens, donor types, and GVHD-prophylaxis regimens are included. Exclusion criteria include history of severe colitis or active inflammatory bowel disease or total colectomy, umbilical cord blood or ex vivo T-cell depletion, exposure to fecal microbiota transplant or any live microbial therapeutic within 3 months prior to screening, and evidence of relapse or progression of hematologic malignancy (minimal residual disease is allowed). Following screening, participants in both cohorts receive 2 treatment courses (one before and one after HCT), each comprised of microbiome conditioning with oral vancomycin or placebo followed by SER-155 or placebo, plus a conditional 3rd treatment course if the subject receives antibiotics. Safety outcomes are followed through 52 weeks post HCT. The primary endpoint is the incidence and severity of adverse events, serious adverse events, and adverse events of special interest. Secondary endpoints include rates of BSI, gastrointestinal infections, aGvHD, febrile neutropenia and overall survival. Microbiome related endpoints include engraftment of SER-155 bacterial strains in the gastrointestinal tract (PK endpoint) and fecal microbiome diversity, composition and metabolites. Results: Cohort 1 enrollment is complete, with 13 participants receiving SER-155. In December 2022, the Data and Safety Monitoring Committee supported continuation to Cohort 2 enrollment following review of safety data from Cohort 1. Enrollment in Cohort 2 is underway. Conclusions: This Phase 1b study is designed to assess the safety, and clinical efficacy of SER-155 in allogeneic HCT, expanding the clinical experience of microbiome- directed interventions in allogeneic HCT recipients. Clinical trial information: NCT04995653 .