Disruption of the intestinal microbiota occurs frequently in allogeneic hematopoietic cell transplantation (allo-HCT) recipients and predisposes them to development of graft-versus-host disease (GvHD). In a prospective, single-center, single-arm study, we investigated the effect of donor fecal microbiota transplantation (FMT) on symptoms of steroid-refractory or steroid-dependent, acute or late-onset acute intestinal GvHD in 15 individuals who had undergone allo-HCT. Study participants received a fecal suspension from an unrelated healthy donor via nasoduodenal infusion. Donor FMT was well tolerated, and infection-related adverse events did not seem to be related to the FMT procedure. In 10 of 15 study participants, a complete clinical response was observed within 1 month after FMT, without additional interventions to alleviate GvHD symptoms. This response was accompanied by an increase in gut microbial α-diversity, a partial engraftment of donor bacterial species, and increased abundance of butyrate-producing bacteria, including Clostridiales and Blautia species. In 6 of the 10 responding donor FMT recipients, immunosuppressant drug therapy was successfully tapered. Durable remission of steroid-refractory or steroid-dependent GvHD after donor FMT was associated with improved survival at 24 weeks after donor FMT. This study highlights the potential of donor FMT as a treatment for steroid-refractory or steroid-dependent GvHD, but larger clinical trials are needed to confirm the safety and efficacy of this procedure.

Key Points Ecto+ ILC neutralize extracellular ATP and suppress autologous T cells via the production of adenosine. Human acute GVHD is associated with a depletion of tissue ecto+ ILC3 and a reduction in serum adenosine levels.

Microbiota injury occurs in many patients undergoing allogeneic hematopoietic cell transplantation, likely as a consequence of conditioning regimens involving chemo- and radiotherapy, the widespread use of both prophylactic and therapeutic antibiotics, and profound dietary changes during the peri-transplant period. Peri-transplant dysbiosis is characterized by a decrease in bacterial diversity, loss of commensal bacteria and single-taxon domination (e.g., with Enterococcal strains). Clinically, deviation of the post-transplant microbiota from a normal, high-diversity, healthy state has been associated with increased risk of bacteremia, development of graft-versus-host disease and decreases in overall survival. A number of recent clinical trials have attempted to target the microbiota in allogeneic hematopoietic cell transplantation patients via dietary interventions, selection of therapeutic antibiotics, administration of pre- or pro-biotics, or by performing fecal microbiota transplantation. These strategies have yielded promising results but the mechanisms by which these interventions influence transplant-related complications remain largely unknown. In this review we summarize the current approaches to targeting the microbiota, discuss potential underlying mechanisms and highlight the key outstanding areas that require further investigation in order to advance microbiota- targeting therapies.

Introduction: Severe acute graft-versus-host disease (aGVHD) is characterized by an imbalance of circulating tissue repair factors, with elevated amphiregulin (AREG) and very low (<10 pg/ml) plasma epidermal growth factor (EGF). We hypothesized that giving supplemental EGF, contained in an inexpensive, commercially available drug (urinary-derived human chorionic gonadotropin [hCG], Pregnyl Ò) in addition to standard aGVHD therapy would improve outcomes. Patients and Methods: Twenty-six patients received hCG/EGF in addition to standard aGVHD therapy (13 with Minnesota high risk aGVHD and 13 receiving 2 nd line therapy). In both cohorts, patients with a complete or partial response (CR/PR) at the end of the initial dosing period were eligible to receive maintenance hCG/EGF SQ twice weekly for up to 5 weeks. Initial hCG dosing was at 500 units hCG/m 2 SQ, escalating to 2,000 units hCG/m 2 in cohorts of 2, with dose assignment by the continual reassessment method. We analyzed GVHD-associated plasma biomarkers during therapy. Results: HCG/EGF was well tolerated, with no dose-limiting toxicities. At day 28 of study, responses for initial therapy were 8/13 CR (62%), 0/13 PR (0%), and 5/13 NR (38%), higher than institutional historical (n=269) 26% CR, 16% PR, 57% NR (Figure 1A). Responses for 2 nd line therapy were 7/13 CR (54%), 1/13 PR (8%), 5/13 NR (38%), 4 of which were deaths (31%), improved relative to historical outcomes (n=85) of 18% CR, 19% PR, 63% NR (including 16% deaths, Figure 1A). In initial therapy patients, plasma EGF rose from baseline 3 pg/ml to 25.4 pg/ml at 6 hours post-hCG/EGF dose (p=0.02), while in 2 nd line patients, plasma EGF never rose from baseline 5 pg/ml. Patients with a day 28 CR/PR had a 4.6-fold reduction in plasma AREG over time (Figure 1B). Conclusions: HCG/EGF is a novel adjunct therapy in lifethreatening aGVHD. The mechanisms of benefit may include facilitation of tissue repair with detectable increases in circulating EGF. The optimal dose and duration of hCG/EGF are under investigation, with ongoing dose escalation in patients with steroid-refractory aGVHD based upon these results. Decreasing plasma AREG may reflect successful treatment of severe aGVHD.