KN046 in Patients With Recurrent or Metastatic Esophageal Squamous Cell Carcinoma

Inclusion Criteria: * Signed inform consent form(ICF) * Age ≥ 18 years and ≤ 75 years, male or female * Histologically or cytologically documented recurrent or metastatic esophageal squamous cell carcinoma, with indications of radiotherapy and without prior systemic treatment * At least one measurable lesion according to Response Evaluation Criteria In Solid Tumors（RECISIT） v 1.1 * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Adequate organ function * Female patients and males with partners of childbearing potential should be using highly effective contraceptive measures (failure rate of less than 1% per year). Contraception should be continued for a period of 24 weeks after dosing has been completed. * Ability to comply with treatment, procedures and pharmacokinetics (PK) sample collection and the required study follow-up procedures Exclusion Criteria: * Known brain metastasis or another Central Nervous System (CNS) metastasis that is either symptomatic or untreated. * Patients who are participating or have participated in a study of an investigational drug within 4 weeks prior to the first dose of trial treatment. * Patients who have received immune checkpoint proteins/antibody/medicine for treatment. * Patients who have interstitial lung disease, or a history of pneumonitis that required oral or intravenous glucocorticoids to assist with management. * Subjects with active autoimmune diseases or history of autoimmune diseases should be excluded * Active Hepatitis B Virus (HBV) or Hepatitis C Virus (HCV) infection. * Known HIV infection or known history of acquired immune deficient syndrome (AIDS) * Any unresolved the Common Terminology Criteria for Adverse Events (CTCAE) Grade ≥ 2 toxicities from prior anti-cancer therapy except for vitiligo, alopecia * Patients who have serious hypersensitive reaction to monoclonal antibodies and have history of uncontrolled allergic asthma