• aged 18\

⁃ 75

• ECOG score 0\

⁃ 2

• biopsy diagnosed rectal adenocarcinoma, distal margin within 10cm to anal verge

• no distant metastasis, staged II/III (T4b excluded) by MRI

• maximum diameter of rectal cancer lesion≥10mm according to baseline CT or MRI (i.e. a measurable lesion as per RECIST 1.1 criteria)

• willing and able to comply with study protocol

• consent to the use of blood and tissue specimens for study

• no history of previous anti-tumor treatment (e.g. radiation, chemo, immuno, bio, herbal, etc.)

• no disorders/diseases of immune system (e.g. systemic lupus erythematosus, rheumatoid arthritis, systemic vasculitis, scleroderma, pemphigus, dermatomyositis, mixed connective tissue disease, autoimmune hemolytic anemia, hyperthyroidism/hypothyroidism, ulcerative colitis, autoimmune hemolytic anemia, HIV infection, etc.)

• no significant dysfunction of major viscera (e.g. heart, lung, liver, kidney, etc.)

• no jaundice or gastrointestinal obstruction

• no acute/ongoing infection

• no significant irregularities in blood routine test and biochemical test results, particular requirements include: neutrophils≥1.5×109/L, HGB≥80g/L, platelet≥100×109/L, serum creatinine≤1.5×ULN, total bilirubin≤1.5×ULN, ALT、AST≤2.5×ULN

• no social or mental disorder

• for women of child-bearing age, a negative result of serological pregnancy test is required, and effective contraception measures from inclusion till 60 days after the last dose of study drug is required