This is a single-arm, open-lable, multicenter phase I/IIa clinical trial evaluating the safety, tolerability, pharmacokinetics, and preliminary efficacy of PM1003 in the treatment of advanced solid tumors.

PM1003 is a Bispecific Antibody Targeting PD-L1 and 4-1BB.

Inclusion Criteria:

1. Voluntary participation in clinical study; fully understand the study and sign informed consent voluntarily; willing to follow and able to complete all test procedures;
2. Male or female aged 18 to 75 years;
3. Subjects with malignant tumor confirmed by histology or cytology;
4. Adequate organ function;
5. ECOG score was 0-1.
6. Pre-menopausal female subjects with negative blood pregnancy results within 7 days prior to the study treatment, and agree to abstain from sex or use medically approved effective contraceptive measures for 6 months from the date of signing the informed consent form to the end of the last medication;
7. Male subjects are agree to abstain from sex or use medically approved effective contraceptive methods for 6 months from the date of signing the informed consent form to the end of the last medication, and do not donate sperm during this period.

Exclusion Criteria:

1. History of severe allergic to macromolecular protein drugs, severe allergy to drugs or known allergy to any component of the drug in this study;
2. Treatment with any 4-1BB monoclonal antibody or 4-1BB-containing dual antibody immune co-stimulatory molecule agonist;
3. Current active infection requiring intravenous anti-infective therapy;
4. Current presence of uncontrolled pleural, pericardial, and peritoneal effusions;
5. Known history of alcohol abuse, psychotropic drug abuse or drug abuse;
6. History of neurological or psychiatric disorders, such as epilepsy, dementia, schizophrenia, etc.;
7. Anticipated need for any other form of antineoplastic drug treatment during the trial;
8. Women who are pregnant or breastfeeding;
9. Other conditions lead to inappropriate to participate in this study as judged by the investigator.