Neoadjuvant Short-Course Radiotherapy Followed by CAPOX Plus PD-1 Antibody and IL-2 in Locally Advanced Rectal Cancer (PRIDE01)

Inclusion Criteria: * Age 18 to 70 years at enrollment. * Histologically confirmed rectal adenocarcinoma with the inferior tumor border within 12 cm of the anal verge. * Pelvic MRI stage T3-T4, or any T stage with regional lymph-node involvement. * Absolute neutrophil count \>=1.5 x 10\^9/L and platelet count \>=75 x 10\^9/L. * Total bilirubin \<=1.5 x the upper limit of normal; aspartate aminotransferase and alanine aminotransferase \<=2.5 x the upper limit of normal. * Serum creatinine \<=1.5 x the upper limit of normal. * Eastern Cooperative Oncology Group performance status 0 or 1. * Ability and willingness to provide written informed consent. Exclusion Criteria: * Distant metastatic disease. * Recurrent rectal cancer. * Tumor-related bleeding or perforation, or another condition requiring emergency surgery. * Previous systemic anticancer treatment for rectal cancer. * A concurrent malignancy other than colorectal cancer. * Active autoimmune disease, or a history of autoimmune disease requiring systemic corticosteroids or other immunosuppressive therapy. * Interstitial lung disease, non-infectious pneumonitis, or another uncontrolled systemic disease. * Unresolved toxicity of grade 2 or higher from previous treatment, except anemia, alopecia or pigmentation changes. * Previous treatment targeting PD-1, PD-L1 or CTLA-4. * Pregnancy or breastfeeding. * Human immunodeficiency virus infection or acquired immunodeficiency syndrome. * Known hypersensitivity to any protocol t…