A Study of CS1001 in Subjects With Relapsed or Refractory Extranodal Natural Killer/ T Cell Lymphoma(ENKTL)

Inclusion Criteria: 1. Subject must have a histologically confirmed NKTL at study site. 2. Subject must have relapsed or refractory NKTL after prior asparaginase-based chemotherapy or chemo radiotherapy. 3. Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1. 4. Subject must have at least one evaluable or measurable lesion per Lugano 2014 classification. 5. Subject must have adequate organ function and bone marrow function without severe hematopoietic disorder, or heart, lung, liver or kidney dysfunction or immune deficiency. 6. Subject must provide stained tumor tissue sections and corresponding pathological report or unstained tumor tissue sections (or tissue block) for central pathology review. 7. Subject with prior anti-cancer treatment can only be enrolled when the toxicity of prior anti-cancer treatment has recovered to baseline or ≤ Grade 1 according to Common Terminology Criteria for Adverse Events (CTCAE) v4.03. Exclusion Criteria: 1. Invasive natural killer leukemia. 2. Concomitant with hemophagocytic syndrome. 3. Primary site in central nervous system (CNS) or CNS involvement. 4. Subjects currently participating in other clinical studies or use of any investigational drug within 4 weeks prior to the first dose of CS1001. 5. Subjects who received systemic corticosteroid or any other immunosuppressive therapy within 14 days prior to the first dose of CS1001. 6. Subjects who had prior chemotherapy, immune therapy, biological therapy as systemic treatment for cancer, within 28 days prior to the first dose of CS1001. 7. Receipt of traditional medicinal herbal preparations with anti-tumor indications with 7 days prior to the first dose of CS1001. 8. Known history of human immunodeficiency virus (HIV) infection and/or acquired immune deficiency syndrome. 9. Subjects with active hepatitis B or C infection. 10. Subjects with active tuberculosis infection. 11. Subjects who received prior therapy with anti-PD-1, anti-PD-L1 or anti-CTLA-4 monoclonal antibody. 12. Female subjects who are pregnant or breast-feeding. For more information regarding trial participation, please contact at cstonera@cstonepharma.com