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
