Study of GV20-0251 in Participants With Solid Tumor Malignancies

Inclusion Criteria: * Before conducting any study-specific procedures, voluntarily sign an informed consent form. * Be able and willing to participate throughout the entire study period and comply with study procedures. * participants ≥18 years of age * Previously treated, histologically-confirmed advanced solid malignancy with progressive disease requiring therapy (Refractory or intolerant to standard therapies, must have received the standard of care therapy) * Participants must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST version 1.1) * For participants who have received prior treatment with a checkpoint inhibitor there must be documented disease progression * ECOG performance status of 0 or 1 before C1D1 * Part B Participants must be willing to provide fresh tumor biopsy (core biopsy) both pre-treatment and on-treatment, if clinically feasible * Disease-free of active second/secondary or prior malignancies for ≥ 2 years Laboratory test results within the required parameters * Women of childbearing potential (WOCBP) and men must agree to use adequate contraception Exclusion Criteria: * Participants with acute leukemia or CLL * Participant with heart disease (NYHA ≥ Level II), myocardial infarction within the past 6 months, or unstable arrhythmia * Fridericia-corrected QT interval (QTcF) \> 470 msec, or the presence of congenital long QT syndrome, or a history of clinically significant electrocardiogram (ECG) abnormalities (including pericarditis) that, in the investigator's judgment, may affect the subject's safety. * Active, uncontrolled bacterial, viral, or fungal infections requiring systemic therapy within 7 days before C1D1 * Participant has active autoimmune disease or other medical conditions requiring chronic systemic steroid or immunosuppressive therapy * Known human immunodeficiency virus (HIV) infection, known hepatitis B virus (HBV), or hepatitis C virus (HCV) infection, unless meeting the specific conditions. * History of major organ transplant and/or a bone marrow transplant * Symptomatic central nervous system (CNS) malignancy or metastasis * Serious nonmalignant disease * Pregnant or nursing women * Major surgery within 28 days prior to the first dose of study medication * Prior anticancer therapy within 4 weeks or 5 half-lives (whichever is shorter) before the first dose of GV20-0251 on Cycle 1 Day 1 (C1D1), with the exceptions. * History of severe allergic reactions to biologic therapy, which in the investigator's judgment may increase the subject's risk. * Radiation therapy for symptomatic lesions within 14 days prior to C1D1 dosing. * Active substance abuse * Any history of an immune-related ≥ Grade 3 AE attributed to prior cancer immunotherapy