A Prospective, Multicenter, Single-Arm Phase II Exploratory Study of Serplulimab Combined With Oncolytic Virus H101, Short-Course Radiotherapy, and XELOX Chemotherapy as Total Neoadjuvant Treatment for Locally Advanced (cT1-3N0M0) Rectal Cancer

Other illness

• Participants will be excluded if they meet any of the following criteria:
  • Histology other than rectal adenocarcinoma (e.g., gastrointestinal stromal tumor, lymphoma).
  • Prior pelvic radiotherapy.
  • Prior treatment with PD-1, PD-L1, or CTLA-4 inhibitors.
  • Known allergy to study drugs or their components.
  • History of other malignancies, except adequately treated non-melanoma skin cancer, carcinoma in situ of the cervix, or papillary thyroid carcinoma.
  • Active autoimmune disease or history of autoimmune disease requiring systemic treatment.
  • Immunodeficiency, including HIV infection, or history of organ transplantation.
  • History of interstitial lung disease or non-infectious pneumonitis.
  • Active tuberculosis infection or history of untreated tuberculosis.
  • Active hepatitis B or hepatitis C infection.
  • Severe cardiovascular, pulmonary, or renal disease.
  • Uncontrolled hypertension despite medication.
  • History of substance abuse (alcohol or drugs).
  • Active uncontrolled infection.
  • Use of systemic immunosuppressive therapy.
  • Pregnant or breastfeeding women.
  • Any condition that, in the investigator's opinion, may interfere with study participation or safety.

• \- Participants must meet all of the following criteria:
• Age 18 to 80 years, male or female.
• Histologically confirmed low rectal adenocarcinoma, with tumor located ≤5 cm from the anal verge.
• Clinical stage T1-3N0M0 according to AJCC staging criteria.
• Mismatch repair-proficient (pMMR) or microsatellite stable (MSS) tumor confirmed by immunohistochemistry or genetic testing.
• No prior anti-tumor treatment.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-1, with an expected survival of at least 3 months.
• Adequate organ function, including:
  • Absolute neutrophil count ≥1.5 × 10\^9/L
  • Platelet count ≥100 × 10\^9/L
  • Hemoglobin ≥9 g/dL
  • Serum albumin ≥3 g/dL
  • Total bilirubin ≤1.5 × upper limit of normal (ULN)
  • ALT and AST ≤2 × ULN
  • Serum creatinine ≤1.5 × ULN or creatinine clearance ≥60 mL/min
  • INR or PT ≤1.5 × ULN, and aPTT ≤1.5 × ULN
• Thyroid function within normal range or adequately controlled.
• Negative pregnancy test for women of childbearing potential.
• Willingness to use effective contraception during the study and for 12 months after treatment.
• Ability to understand and willingness to sign a written informed consent form.
• Willingness and ability to comply with study procedures and follow-up.