A Study of ATG-022 in Patients With Advanced/Metastatic Solid Tumors

Inclusion Criteria: 1. Provision of signed and dated, written informed consent prior to any study-specific procedures, sampling, and analyses. 2. Aged at least 18 years as of the date of consent. 3. Histological or cytological confirmation of a solid tumor, and have progressed despite standard therapy(ies), or are intolerant to standard therapy(ies), or not applicable for standard therapy(ies). 1. Dose Escalation Phase: all solid tumors. 2. Dose Expansion Phase: Claudin 18.2 positive solid tumors. 4. Subjects should be willing to receive a biopsy at screening, if no former available tumor tissue samples within 36 months prior to participating in the study are provided. 5. At least 1 measurable lesion per Response Evaluation Criteria In Solid Tumors (RECIST) v1.1. 6. Estimated life expectancy of a minimum of 12 weeks. 7. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 . 8. Females should be using adequate contraceptive measures until 180 days after the end of treatment, should not be breastfeeding, and must have a negative pregnancy test prior to the start of dosing if of child-bearing potential or must have evidence of nonchild-bearing potential by fulfilling one of the following criteria at screening 9. Male subjects should be willing to use effective contraception, ie condoms, for the duration of the study and 180 days after the final dose of study treatment. Exclusion Criteria: 1. Primary central nervous system disease or central nervous system metastatic disease. 2. Prior exposure to a Claudin 18.2 targeting agent. 3. Prior therapy with any chemotherapy, immunotherapy, anticancer agents, or investigational products from a previous clinical study within 28 days of the first dose of study treatment or within a period during which the investigational product or systemic anticancer treatment has not been cleared from the body (eg, a period of 5 'half-lives'. 4. Prior vaccination within 28 days of the first dose of study therapy. 5. Prior any solid organ transplant. Autologous stem cell transplant or CAR-T cell infusion \< 6 months prior to the first dose of study treatment. 6. Active infection including hepatitis B, and/or hepatitis C. 7. Known history of human immunodeficiency virus (HIV) infection. 8. Any unresolved toxicities from prior therapy greater than Grade 1 at the time of ICF signature, with the exception of alopecia. 9. Pregnant or nursing females. 10. History of hypersensitivity or history of allergic reactions attributed to drugs with a similar chemical or biologic structure or class to ATG-022. 11. Other primary malignancies developed within 5 years prior to the first dose of the study drug, except locally curable malignancies after radical treatment . 12. In the opinion of the investigator, subject's complications, or other conditions (psychological, familial, sociological, or geographical etc.) may affect protocol compliance or may be unsuitable for participation in the study.