To Explore a Single-arm Phase II Study on Intestinal Microbiota Transplantation Combined With Neoadjuvant Immunotherapy and Chemoradiotherapy for Locally Advanced Rectal Cancer Under MSS/pMMR

To evaluate the pathological complete response rate (pCR) of intestinal flora transplantation combined with short-course radiotherapy +CAPOX+ sintilimab in neoadjuvant therapy for locally advanced rectal cancer (pMMR/MSS type)

Inclusion Criteria: 1. ECOG PS 0-1 2. The lower edge of the tumor is ≤12cm from the anal margin. After multidisciplinary assessment, R0 resection is possible 3. RAS/BRAF wild type, pMMR/MSS status 4. Patients of childbearing age need to take effective contraceptive measures. 5. Voluntarily sign the informed consent form Exclusion Criteria: 1. dMMR/MSI-H type 2. Has previously received anti-tumor treatment (including surgery, radiotherapy, chemotherapy, targeted therapy or immunotherapy); 3. Active autoimmune diseases, inflammatory bowel disease; 4. Active infection, immune deficiency, severe liver and kidney dysfunction; 5. Severe intestinal obstruction, perforation or requiring emergency surgery; 6. Pregnant or lactating women; 7. Contraindications related to FMT (such as recent use of high-dose immunosuppressants, severe neutropenia, etc.); 8. Other circumstances where participation in clinical trials is not suitable