This is a multi-center, open-label, phase 1/2 study to evaluate the safety, efficacy, and pharmacokinetic (PK)/pharmacodynamic (PD) characteristics of HY07121 in participants with advanced solid tumors.

The study starts with a dose escalation part (Part 1) followed by a dose expansion part (Part 2). The main purpose of this study is to evaluate the safety and tolerability of the drug HY07121 and determine the maximum tolerated dose (MTD) (if any) and/or the recommended dose(s) (RD) and preliminary anti-tumor activity. Additional purposes of the study are to evaluate the pharmacokinetics (PK) properties, immunogenicity, correlation of the biomarkers and PK profile with anti-tumor activity.

Inclusion Criteria:

• Written informed consent;
• ≥18 years old and ≤80 years old, gender: male or female;
• Histologically or cytologically confirmed unresectable advanced/metastatic solid tumor that has relapsed or progressed on or after standard systemic treatments, or refused the standard treatment, or for which no standard treatment is available;
• Presence of at least one measurable lesion according to Response Evaluation Criteria in Solid Tumours (RECIST) Version 1.1;
• Eastern Cooperative Oncology Group (ECOG) performance status score is 0 or 1;
• Life expectancy ≥3 months;
• Participant must have adequate main organ function;
• Fertile female patients must have a negative serological pregnancy test within 7 days before the first dosing and be willing to use effective birth control/contraception to prevent pregnancy during the study period up to 6 months after the last dosing of the study. Male patients must agree to have no sperm donation plans and to use effective contraceptive methods during the study period until 6 months after the last dose of the study. Postmenopausal women must have amenorrhea for at least 12 months before they are considered infertile.

Exclusion Criteria:

• Within the defined washout periods for prior anti-cancer treatments;
• Participant is currently participating or has participated in a study of an investigational agent or using an investigational device within 4 weeks of first dose of HY07121.
• Any other malignancy within 2 years prior to the first dose of the study treatment except for localized cancers that are considered to have been cured and in the opinion of the Investigator present a low risk for recurrence.
• Participant has not recovered (i.e., to Grade 1 or to baseline) from previous anticancer therapy-induced Adverse Events (AEs).
• Participants with a history of recently (within previous 2 years of the first dose of the study treatment) active diverticulitis or symptomatic peptic ulcer disease;
• Major surgery within 4 weeks of receiving the first dose of study treatment;
• Participant has Symptomatic Central Nervous System (CNS) metastases, or CNS metastases requiring CNS-directed local therapy (such as radiotherapy or surgery) or corticosteroids therapy within 4 weeks of first dose of study treatment;
• Participants with untreated or under treatment for tuberculosis, including but not limited to tuberculosis; Patients who have received standardized anti-tuberculosis treatment and have been confirmed cured by the researchers can be included;
• Participants with clinically significant cardiovascular diseases, in the past 6 months prior to the first dose of the study treatment; symptomatic coronary heart disease requiring drug treatment; arrhythmia requiring drug treatment; or uncontrolled hypertension;
• Known Human Immunodeficiency Virus (HIV) infection or known Acquired Immunodeficiency Syndrome (AIDS);
• Active or chronic hepatitis B or hepatitis C infection; treponema pallidum antibody positive, and confirmed positive test;
• Active known or suspected autoimmune disease.
• History of non-infectious pneumonitis that has required a course of oral or intravenous steroids to assist with recovery, or interstitial lung disease or severe obstructive pulmonary disease;
• History of severe allergy;
• History of allogeneic organ transplantation or graft-versus-host disease;
• Have received live/attenuated vaccines and mRNA vaccines within 4 weeks prior to screening or plan to receive live/attenuated vaccines and mRNA vaccines during the study period;
• Any active infection requires systemic treatment via intravenous infusion within 4 weeks prior to the first dose of study treatment;
• Known psychiatric disorder or drug abuse that would interfere the trial requirements;
• Participant with uncontrolled pleural effusion, pericardial effusion or peritoneal effusion or need drainage;
• In addition to the tumors present at the time of entry into the study, other active malignancies were present within 3 years prior to the first dose (not excluding locally cured tumors, such as skin basal cell carcinoma, superficial bladder cancer or carcinoma in situ of the breast, etc.);
• Participants considered unsuitable for participation in this study by the investigators.