Treatment of Relapsed or Refractory Natural Killer/T Cell Lymphoma

Inclusion Criteria: * Age range 14-70 years old; ECOG performance status 0-2; Estimated survival time \> 3 months * Histological confirmed evidence of relapsed or refractory NK/T cell lymphoma * Before enrollment, representative formalin-fixed paraffin-embedded tumor samples (or 15 tissue sections at least) and related pathological reports are needed * Previous treatment with at least one chemotherapy regimen * At least one measurable lesion * None of other serious diseases, cardiopulmonary function is normal * Pregnancy test of women at reproductive age must be negative * Patients could be followed up * None of other relative treatments including the traditional Chinese medicine, immunotherapy, biotherapy except anti-bone metastasis therapy and other symptomatic treatments. * volunteers who signed informed consent. * No anti-PD1 antibody contraindication (All of the following tests are required to be finished within 14 days prior to the first research): 2.5×109/L\<WBC\<15×109/L, hemoglobin ≥ 90 g/L, neutrophil≥ 1.5×109/L, lymphocyte≥0.5×109/L, platelet ≥ 100×109/L, serum albumin≥2.5g/dL, ALT and AST ≤ 2×ULN, serum bilirubin≤ 1.5×ULN, serum creatine ≤ 1.5×ULN, Serum Albumin ≥ 30g/L, serum plasminogen is normal, creatinine clearance rate≥30 mL/min, INR≤1.5×ULN, APTT≤1.5×ULN Exclusion Criteria: * Disagreement on blood sample collection * Patients allergic of chimeric or humanized antibody * Pregnant or lactating women * Serious medical illness likely to interfere with participation * Serious infection * Primitive or secondary tumors of central nervous system * The evidence of CNS metastasis * History of peripheral nervous disorder or dysphrenia * History of active autoimmune disease and a concomitant second cancer * patients participating in other clinical trials * patients taking other antitumor drugs * patients estimated to be unsuitable by investigator