Inclusion Criteria:
1. Males or females, aged \> 18 years.
2. Histologically- or cytologically-confirmed non-small cell lung cancer that has progressed after first line systemic therapy.
3. Malignant pleural effusion diagnosed histologically or cytologically, with moderate or above moderate pleural fluid (sitting pleural fluid depth ≥ 4 cm via ultrasound, expected pleural fluid volume ≥ 500 mL) . Require clinical intervention and not treated yet.
4. Patients who have an washout period of ≥ 4 weeks or 5 half-life of the drug (including radiotherapy, chemotherapy, immunotherapy, biologic, targeted, hormonal therapy, and 14 days for local radiotherapy) between the last systemic therapy and the first dose; however, no washout period is required if the subject has new pleural fluid or poor control of current pleural fluid after at least 2 cycle systemic therapy.
5. Patients who had recovered to grade 0-1 of any toxic reaction to prior antineoplastic therapy as determined by the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) V5.0, with the exception of alopecia, hyperpigmentation and ≤ grade 2 neuropathy, hormone replacement hypothyroidism or other adverse events confirmed to have turned chronic.
6. Patients with physical status ECOG score (PS) of 0-2.
7. Patients with life expectancy ≥ 12 weeks.
8. Bone marrow: absolute neutrophil count (ANC) ≥ 1.5 ×10\^9/L, platelet count ≥ 100 ×10\^9/L, hemoglobin ≥ 8.5 g/dL (without blood transfusion within14 days of the first dose of study drug); Liver: bilirubin (TBIL)≤ 1.5 x upper limit of normal (ULN), aspartate aminotransferase (AST) and alanine transaminase (ALT) ≤ 3 x ULN ( ≤ 5 x ULN in case of liver metastases); Kidney: serum creatinine ≤1.5 x ULN.
9. Patients must understand and voluntarily sign the written informed consent.
Exclusion Criteria:
1. Patients with asymptomatic pleural fluid and not requiring clinical intervention, or bilateral malignant pleural fluid, or proposed perfusion of the chest cavity presenting with pleural fluid separation.
2. Patients with central nervous system (CNS) metastases resulting in clinical symptoms or requiring therapeutic intervention; patients previously treated for brain metastases may be enrolled if they have been asymptomatic for ≥ 4 weeks prior to the first dose and have imaging indicating stable disease and do not require corticosteroid or anticonvulsant therapy.
3. Patients with a known history of severe allergy to M701 drug components or antibody-like macromolecular drugs.
4. Patients with contraindications to thoracentesis.
5. Patients who have undergone major surgical procedures within 4 weeks prior to the first dose.
6. Patients with extensive liver metastases (\>70%).
7. Patients with uncontrollable active infection (NCI-CTCAE V5.0 ≥ grade 2).
8. Patients required long-term hormonal or immunosuppressive therapy, e.g. active autoimmune disease, maintenance therapy after organ transplantation, except that the following are allowed to enter screening: type I diabetes mellitus, hypothyroidism that can be controlled by replacement therapy only, skin diseases that do not require systemic therapy (e.g. vitiligo, psoriasis or alopecia).
9. Patients with severe respiratory disease which, in the judgment of the investigator, makes them unsuitable for entry; or combined interstitial pneumonia.
10. Patients with history of severe cardiovascular disease, including previous coronary artery bypass grafting or coronary stenting, myocardial infarction within 6 months, congestive heart failure (New York Classification of Cardiac Function Class III-IV) or unstable angina, or uncontrolled hypertension.
11. Patients with QTc interval \> 480 ms,family or personal history of long or short QT syndrome, clinically significant history of ventricular arrhythmias or implantation of a defibrillation device for ventricular arrhythmias.
12. Patients with a history of (non-study tumour) malignancy (except squamous and basal cell carcinoma of the skin, carcinoma in situ of the cervix or breast, or other, non-invasive lesions that the investigator and sponsor agree have been cured and have a minimal risk of recurrence within 3 years) within 3 years prior to the date of first study drug administration.
13. Patients who have active hepatitis B (HBV-DNA quantification ≥ 1 x 10\^4 copies/mL or 2000 IU/mL), active hepatitis C (positive for hepatitis C antibodies and HCV-RNA above the lower limit of detection of the assay), active syphilis with positive HIV antibodies.
14. Pregnant or breastfeeding woman,Plan to conceive within six months;
15. Patients with a confirmed history of neurological or mental disorders, including epilepsy and dementia.
16. Those that are deemed ineligible for this clinical trial by investigator.
