This is a first-in-human (FIH), dose-escalation, PK expansion, monotherapy efficacy expansion, and open-label phase I clinical study assessing the safety, tolerability, pharmacokinetics, immunogenicity, and preliminary efficacy of QL1604 injection （a humanized anti-PD-1 monoclonal antibody）in patients with advanced solid tumors.

Inclusion Criteria:

1. Volunteer to participate in this clinical study; completely understand and know this study as well as sign the informed consent form (ICF);
2. Age ≥ 18 years and ≤ 70 years when ICF is signed;
3. Pts with histologically or cytologically confirmed advanced solid tumors;
4. At least one target lesion as defined per RECIST Version (v) 1.1;
5. Subjects who have disease progression or intolerable reactions after the currently available standard anti-cancer treatment previously received or refused prior cancer therapy regimen(s) ;
6. Eastern Cooperative Oncology Group performance status of 0 or 1;
7. Life expectancy of greater than 12 weeks;
8. Adequate hematologic and organ function;
9. Female subjects who are not pregnant or breastfeeding
10. Male and female subjects able to have children must agree to use highly effective method of contraception throughout the study and for at least 120 days after last dose;

Exclusion Criteria:

1. Known hypersensitivity to any monoclonal antibody, QL1604 and/or any of its excipients;
2. Active autoimmune disease that has required systemic treatment, replacement therapy is acceptable;
3. Subjects with major cardiovascular and cerebrovascular diseases;
4. Any condition that required systemic treatment with either corticosteroids (> 10 mg daily of prednisone or equivalent) or other immunosuppressive medication ≤ 14 days before the first dose of study drug;
5. Subjects who have received surgery, radiotherapy, chemotherapy, targeted therapy, other anti-tumor treatments, or participating in other clinical studies is less than 4 weeks before the first administration of investigational product;
6. Received a live vaccine;
7. Infection with human immunodeficiency virus (HIV);
8. Known psychiatric or substance abuse disorders that would interfere with the requirements of the study;
9. History or current evidence of any condition, therapy, or laboratory abnormality, that might confound the results of the trial, or interfere with the participant's participation for the full duration of the study, or investigators/sponsor consider the subjects are not suitable for this trial.