Inclusion Criteria:

• Able to understand and willing to sign the ICF.
• Male or female subject ≥ 18 years.
• Histologically/cytologically confirmed, locally advanced unresectable or metastatic solid tumors that are refractory to standard therapy, or for which no standard therapy exists.
• Subject has measurable disease per RECIST v1.1.
• ECOG Performance Status 0 to 1
• Subjects with life expectancy of ≥ 3 month
• No herbal/alternative medications prior to the first dose
• Must have adequate hematological, hepatic and renal function as defined in the protocol.
• Prior anti-tumor therapies of different kinds must have stopped before the first dose as defined by protocol
• Effective contraception for both male and female subjects if the risk of conception exists

Exclusion Criteria:

• Pregnant or nursing females.
• Any remaining AEs > grade 1 from prior anti-tumor treatment as per CTCAE v4. 03, with exception of the residual hair loss;
• Received a biologic G-CSF, GM-CSF or erythropoietin within 14 days prior to the first dose of study drug;
• Subjects who had prior treatment with an anti-PD-L1 product
• History of documented autoimmune disease except for autoimmune hypothyroidism and well-controlled Type 1 diabetes mellitus.
• W/o autoimmune condition requiring systemic treatment with immunosuppressive medications within 14 days before the planned first dose of study drug.
• Primacy central nervous system (CNS) malignancy or symptomatic CNS metastases are not allowed, with exceptions defined in protocol.
• Major surgery within the 28-days from the screening
• Subjects with idiopathic pulmonary fibrosis or unresolved active or chronic inflammatory pulmonary disease are excluded.
• History of human immunodeficiency virus (HIV) infection, active hepatitis B or C. HBV carriers
• History of primary immunodeficiency, stem cell or organ transplant, or previous clinical diagnosis of tuberculosis disease.
• Clinically significant acute infections 4 weeks and any infection 2 weeks prior to the first dose administration.
• Known allergies, hypersensitivity, or intolerance to protein-based therapies or with a history of any significant drug allergy
• Subjects who experienced immunotherapy-related adverse events (irAE) grade ≥ 3, or who had to discontinue prior anti-PD-1 treatment due to irAEs of any grade.
• Severe or uncontrolled cardiac disease requiring treatment as defined in protocol
• Any other serious underlying medical, psychiatric, psychological, familial or geographical condition that, in the judgment of the investigator, might impair the subject's benefit from the trial treatment
• Known history of hypersensitivity to any components of the MSB2311 product.