Have a Histologically or cytologically confirmed non-CNS solid tumor that is metastatic or unresectable and for whom there is no available standard therapy.
2. PD-L1 positive expression (Tumor Proportion Score ≥1% or Combined Positive Score ≥1) as assessed by IHC staining with either anti-PD-L1 SP263 or 22C3 antibody.
3. Have at least one lesion, not previously irradiated that can be accurately measured per RECIST version 1.1.
4. ECOG performance status of 0 or 1.
5. Life expectancy ≥3 months before starting BH3120.
6. Age 18 years or older (or country’s legal age of majority if the legal age was >18 years).
7. Adequate renal function, including serum creatinine ≤1.5 x ULN and creatinine clearance of ≥60mL/min as calculated using Cockcroft-Gault formula.
8. Adequate hematologic function defined as:
• ANC ≥1,500/mm3 (≥1.5 x 109/L),
• Platelet count ≥100,000/mm3 (≥100 x 109/L)
• Hemoglobin > 9.0 g/dL (>5.6nmol/L)
Patients must be transfusion independent (i.e., no blood product transfusion for a period of at least 14 days prior to study screening).
9. Adequate liver function, including:
• Total serum bilirubin ≤1.5 x ULN unless the patient has documented Gilbert syndrome,
- Patients with known Gilbert syndrome who have a serum bilirubin ≤3.0 x ULN may be enrolled
• AST and ALT ≤3.0 x ULN,
• ALP ≤2.5 x ULN (≤5.0 x ULN in case of bone metastasis)
10. Stable anticoagulant function,
• INR/PT ≤1.5 x ULN
• PTT ≤1.5 x ULN
11. Serum/urine pregnancy test (for female of childbearing potential) negative at screening and at the Day 1 visit (before the patient receives the investigational product).
12. Male and female patients of childbearing potential must agree to use two (2) highly effective methods of contraception throughout the study and for additional 120 days after the last dose of assigned treatment. Male patient must refrain from donating sperm during this same period.
13. Female patients who do not have childbearing potential (i.e., meet at least one of the following criteria): Have undergone a documented hysterectomy and/or bilateral oophorectomy; Have Complion Document ID: 6843417 medically confirmed ovarian failure or; Achieved post-menopausal status, defined as follows: Cessation of regular menses for at least 12 consecutive months with no alternative pathological or physiological cause; and have a serum FSH level within the laboratory’s reference range for postmenopausal women.
14. Voluntary agreement to provide written informed consent and have willingness and ability to comply with all aspects of the protocol.
15. Patient must be willing and able to provide blood (including PBMC) pre- and post-treatment for analysis of relationship between PK, PD biomarker response and efficacy.
16. Patient must be willing and able to provide archived FFPE tissue or newly obtained tumor tissue during the screening period.
17. Patient must be willing and consent to perform paired biopsy (backfill and exploratory cohort) during the screening and treatment period.

Has received prior therapy with an anti-4-1BB(CD137) agent.
2. CNS primary malignancies, active seizure disorder or spinal cord compression, or carcinomatous meningitis. Patients with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least four weeks prior to screening and any neurologic symptoms have returned to baseline), have no evidence of new or progressing brain metastases prior to study entry. This exception does not include carcinomatous meningitis which is excluded regardless of clinical stability.
3. History of any of the following toxicities associated with a prior immunotherapy:
• Grade ≥3 irAE that was considered related to previous immunotherapy and required immune suppressive therapy;
• Grade ≥2 hepatic function-related adverse event that persisted more than 1 week, and that was considered related to immunotherapy, or required treatment discontinuation or immunosuppressive therapy (previous immunotherapies include any anti-CD137, anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 antibody, or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways).
4. Patient’s interval from prior therapy to the first dose of BH3120 is less than 4 weeks for systemic anticancer therapy including investigational agents (or less than 5 half-lives for investigational/ non-cytotoxic agents, whichever is shorter). Upon discussion with the Medical Monitor, shorter wash-out period may be allowed provided that the patient has adequately recovered from any clinically relevant toxicity.
5. Systemic steroid therapy or any other form of immunosuppressive therapy within 14 days prior to screening, excluding:
Prednisone ≤ 10 mg / day or systemic corticosteroids treatment with equivalent physiological dose
6. Radiation therapy within 14 days prior to screening.
7. Therapeutic or experimental monoclonal antibodies in last 60 days prior to screening.

History of chronic liver disease or evidence of hepatic cirrhosis.
9. Left ventricular ejection fraction (LVEF) <50% of ECHO or MUGA scan.
10. Significant cardiovascular impairment: history of congestive heart failure (Class III or IV as classified by the NYHA (Appendix C), unstable angina, myocardial infarction, or stroke within 6 months of the first dose of study drug; or cardiac ventricular arrhythmia.
11. Significant screening ECG abnormalities including atrial fibrillation (unstable or newly diagnosed), double (left and right) bundle branch block, second degree atrioventricular block type II, third-degree atrioventricular block, Grade ≥ 2 bradycardia, QTcF interval > 470 msec, PR interval > 220 msec, or unstable cardiac arrhythmia requiring medication. Chronic asymptomatic atrial fibrillation stably controlled with medications is permitted.
12. Major surgery within 30 days prior to screening.
13. Has received a live vaccine within 30 days prior to screening.
14. Ongoing or has active infection requiring intravenous treatment with anti-infective therapy or systemic therapy and/or any identified active COVID-19 infection.
15. Has ongoing or suspected autoimmune disease. Subjects with vitiligo, type 1 diabetes mellitus, psoriasis, or hypo- or hyperthyroid diseases not requiring immunosuppressive treatment are eligible.
16. Any prior treatment-related (i.e. chemotherapy, immunotherapy, radiotherapy) clinically significant toxicities that have not resolved to Grade ≤1 per CTCAE v5.0 or prior treatment-related toxicities that are clinically unstable and clinically significant at time of enrollment.
17. Has history of (non-infectious) pneumonitis / interstitial lung disease that required steroids or has current pneumonitis / interstitial lung disease.
18. Prior History of myositis, Guillain-Barré syndrome, or myasthenia gravis of any grade.
19. Uncontrolled hypertension defined as systolic blood pressure ≥160mmHg and/or diastolic blood pressure ≥100mmHg, despite optimal medical management.
20. Venous thrombosis or pulmonary embolism within the last 3 months prior to the screening.
21. Known active and clinically significant bacterial, fungal or viral infection including known human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS)-related illness (HIV testing is not required), immunocompromised patients, including patients who have an active infection requiring system therapy.
Known acute or chronic active hepatitis B [defined as hepatitis B surface antigen (HBsAg) and/or hepatitis B core antibody (HBcAb) positive]; Acute or chronic active hepatitis C virus (HCV) antibody positive; subjects with HCV antibody positive but RNA negative can be enrolled.
22. Known prior or suspected hypersensitivity to any component of BH3120 (4-1BB or PD-L1).
23. Patients who previously had a severe hypersensitivity reaction to treatment with any monoclonal antibody or who are known to be positive for ADA responses.

Any other major illness that, in the investigator's opinion, will substantially increase the risk of the patient by participating in this study.
25. Females who are pregnant or breastfeeding.
26. History of organ allograft (except for corneal transplant) or autologous or allogeneic bone marrow transplant, or stem cell rescue within 3 months prior to the first dose of BH3120.