Safety and preliminary efficacy of different doses of fecal microbiota capsule transplantation combined with anti-PD-1 inhibitor for patients with advanced malignant solid tumors.

e14622 Background: Chemotherapy combined with anti-PD-1 inhibitors has now become the standard first-line(1L) treatment for most malignant solid tumors. However, most Phase III studies have found that overall progression-free survival (PFS) with 1L combined subsequent immuno-maintenance therapy (IMT) is still less than 1 year. Fecal microbiota transplantation (FMT) has been shown to synergize with PD-1 antibodies to enhance efficacy. In this study, we administered oral microbiota capsule transplantation to patients(pts) during 1L IMT to evaluate its safety, preliminary efficacy, optimal dosage, and explore the changes in gut microbiota composition and serum metabolism (ChiCTR2100054928). Methods: This is a dose-escalation, exploratory clinical trial. The donor capsules were derived from the feces of a healthy 10-year-old child from a rural area. Twelve late-stage pan-cancer pts who had received standard 1L chemotherapy + PD-1 antibodies and achieved stable or responsive disease were enrolled. The first 3 patients were in the i group (5 capsules po tid d1-3). If no dose-limiting toxicities (DLTs) were observed, another 3 patients were escalated to the i+1 group (10 capsules po bid d1-3). If no DLTs were observed again, another 3 patients were escalated to the i+2 group (10capsules po tid d1-3), and so forth, until the i+3 dose group (20 capsules po bid d1-3). Simultaneously, patients continued receiving the original PD-1 IMT. Fecal samples were collected at baseline (S0), after 10 days (S1), 25days (S2), and 50days (S3) of FMT. Results: From March 2023 to December 2023, 12 pts were successfully enrolled. As of the data cutoff date (December 31, 2023), the median follow-up time was 9.05 months (6.5-9.5 months), and the median PFS has not been reached, with 3 patients experiencing disease progression. Four patients (33.3%) experienced Grade 1-2 FMT-related toxicities, including diarrhea, bloating, and abdominal pain, with no Grade 3 or higher adverse events observed. Fecal metagenomic sequencing analysis showed that the relative abundance levels of Blautia and Faecalibacterium significantly increased after FMT, peaking at day 25 and remaining higher than pre-transplant levels at day 50. We also found that patients in the i+1 group exhibited the greatest changes in microbial composition before and after transplantation, with high absolute and relative transplantation indices. Further analysis of host serum metabolism revealed an increase in molecules related to fatty acid metabolism, such as L-carnitine, stearic acid, and arachidic acid, especially a more pronounced increase in the i+1 group. Conclusions: This preliminary study demonstrates that the combination of oral microbiota capsule and immunotherapy can open up a more economical, safe, and effective avenue for 1L maintenance immunotherapy in tumors. Clinical trial information: ChiCTR2100054928.