Total Neoadjuvant Treatment Plus SHR1210 for High-risk Rectal Cancer and Biomarker Screening Base on Neoantigen

Inclusion Criteria: * Age ≥ 18 years and ≤70 years. * ECOG Performance status 0-1. * Histologically confirmed diagnosis of adenocarcinoma of the rectum. * The distance from down verge of tumor to anal-rectal junction (ARJ) ≤8cm, or ≤12 cm based on sigmoidoscopy. * Clinical Stage T3c, T3d, T4a or T4b, or EMVI (+) or mrN2 or MRF (+) based on MRI. * No evidence of distant metastases. * No prior pelvic radiation therapy. * No prior chemotherapy or surgery for rectal cancer. * No active infections requiring systemic antibiotic treatment. * No systemic infection requiring antibiotic treatment. * No immune system disease. * ANC \> 1.5 cells/mm3, HGB \> 9.0 g/dL, PLT \> 100,000/mm3, total bilirubin≤ 1.5×ULN, AST≤ 2.5×ULN, ALT ≤ 2.5×ULN. * Serum creatinine is within 1.5 times the physiological range， creatinine clearance rate≥50 ml/min * Patients with controllable hypertension were included. * Patients who did not receive anticoagulant therapy: INR, aPTT is required to be within the 1.5 times the physiological range;Patients who receive anticoagulant therapy: INR, aPTT is required to be within the physiological range. * FT3, FT4, TSH are Normal or abnormal without clinical significance. * ECG examination is Normal or abnormal without clinical significance; Echocardiography shows that LVEF\>50%. * Patients must read, agree to, and sign a statement of Informed Consent prior to participation in this study. * Patients show good adherence, follow -up on time. It is recommended that all patients provide tumor tissue samples (preferably fresh tissue samples) for pathological genetic testing prior to enrollment. * Fertile men or women with potential for pregnancy must use highly effective contraception throughout the trial. And continue contraception for 12 months after treatment ends. Exclusion Criteria: * Recurrent rectal cancer. * Anticipated unresectable tumor after neoadjuvant treatment. * Patients with a history of a prior malignancy within the past 5 years, except for adequately treated basal cell or squamous cell skin cancer. * Patients with a history of any arterial thrombotic event within the past 6 months. This includes angina (stable or unstable), MI, TIA, or CVA. * Other Anticancer or Experimental Therapy. * Women who are pregnant or breast-feeding. * Patients with any other concurrent medical or psychiatric condition or disease which would make them inappropriate candidates for entry into this study. * Patients with a history of anti-PD-1, anti-PD-L1, anti-PD-L2 or CEGFR TKI therapy. * Patients underwent major surgery or had not recovered from the side effects of this surgery, received a vaccine, received immunotherapy within 4 weeks before the first use of the study drug, and received radiotherapy within 2 weeks. * Patients who received hematopoietic stimulating factors therapy, such as G-CSF and erythropoietin, within 1 week before the first administration of the study drug. * Patients are allergic to study medication and its ingredients. * Patients have active lung disease (such as interstitial pneumonia, pneumonia, obstructive pulmonary disease, asthma) or active tuberculosis. * Patients have any uncontrollable clinical problems, including but not limited to: 1. Persistent or severe infection. 2. Hypertension that can't be effectively controlled by drugs（ blood pressure reading of 150 over 90）. 3. Uncontrolled diabetes 4. Heart disease (Class III / IV congestive heart failure or cardiac block as defined by the New York Heart Association) 5. Patient has or is suspected of having an autoimmune disease,Such as pituitary inflammation, colitis, hepatitis, nephritis, hyperthyroidism, hypothyroidism, etc. * Patients have other serious, acute or chronic diseases or have abnormal test results, and the investigator judges that this may increase the patient's risk of participating in the trial or interfere with the results.