Synergistic Modulation of the Tumor Microenvironment by Ultrasound-Assisted Fecal Microbiota Transplantation to Reverse Anti-PD-1 Resistance in Colorectal Cancer.

[BACKGROUND] Colorectal cancer (CRC) development and therapy resistance are heavily controlled by the tumor microenvironment (TME). Although anti-PD-1 immunotherapy has significant therapeutic advantages, resistance remains a key challenge. Recent research has identified the gut microbiota as a key regulator of host immunity and checkpoint inhibitor effectiveness. Ultrasound (US) has emerged as a viable biophysical technique for improving medication and microbial delivery and controlling immune activation within tumors.

[OBJECTIVES] The purpose of this work was to assess the synergistic effects of US-assisted fecal microbiota transplantation (US-FMT) on TME remodeling and anti-PD-1 resistance in a CRC cell line-derived xenograft mouse model.

[MATERIALS AND METHODS] Tumor-bearing mice were randomized into four treatment groups: vehicle control, anti-PD-1 alone, fecal microbiota transplantation (FMT) alone, and US-FMT plus anti-PD-1 therapy. Low-intensity focused US was utilized to promote microbial engraftment and intestinal permeability. Flow cytometry, ELISA, and transcriptome profiling were used to investigate tumor growth kinetics, immune cell infiltration, cytokine profiles, and TME-related gene expression.

[RESULTS] In comparison with the other groups, US-FMT reduced tumor development and restored sensitivity to anti-PD-1 treatment. US facilitated beneficial microbial colonization, boosted CD8 T cell infiltration, and decreased immunosuppressive cell populations. Furthermore, US-FMT modified cytokine release and reduced pro-tumorigenic inflammatory mediators, reprogramming the TME to be immune-active.

[CONCLUSIONS] US-assisted microbiota manipulation is a unique and synergistic biotherapeutic method for reversing immunological resistance in CRC. The combination of US and FMT has translational promise for enhancing immunotherapy response and developing noninvasive cancer treatment techniques.