This is a first-in-human Phase 1, single-arm, open-label, multicenter, multiple-dose, dose-escalation study of ABL103 to evaluate the safety, tolerability, MTD (maximum tolerated dose) and/or RP2D (recommended phase 2 dose), pharmacokinetics, immunogenicity, preliminary antitumor activity of ABL103 in subjects with any progressive locally advanced(unresectable) or metastatic solid tumor who are relapsed or refractory following the last line of treatment and have no available standard of care option. This study includes 2 parts: a dose-escalation part and tumor-expansion part

Inclusion Criteria:

• Subject must understand and be willing to provide informed consent and be able to comply with the study procedures and restrictions.
• Subject must be ≥18 years of age on the day of signing the informed consent form (ICF)
• Subject must have a histologically confirmed locally advanced unresectable, or metastatic solid tumor.
• Subject must be relapsed or be refractory to available standard therapy or they must be intolerant of available standard therapy.
• Subject must meet Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1.
• Subject must have an estimated life expectancy of at least 12 weeks.
• Subjects must be recovered from AEs from prior therapy to Grade 1 or the baseline grade more than 14 days prior to the first administration of the study drug, except alopecia or Grade 2 toxicities that are deemed stable or irreversible (eg, peripheral neuropathy)
• Subjects must have adequate hematologic, renal, hepatic, and thyroid functions confirmed based on the screening laboratory test within 7 days prior to the first administration of ABL103.

Exclusion Criteria:

• Subject has received prior anticancer monoclonal antibody treatment or investigational therapy within 28 days prior to the first administration of study drug.
• Subject has received prior chemotherapy or radiation therapy within 2 weeks or targeted small molecule therapy within 5 half-lives prior to the first administration of study drug.
• Subject requires or has received systemic steroid therapy or any other immunosuppressive therapy within 14 days prior to study drug administration.
• Subject has a history of drug-induced pneumonitis (interstitial lung disease) or currently has pneumonitis.
• Subject has risk factors for bowel obstruction or bowel perforation, including, but not limited to a history of acute diverticulitis, intra-abdominal abscess, and abdominal carcinomatosis.
• Subject discontinued from prior immunomodulatory therapy due to any intolerable immune-related adverse events (irAEs) requiring systemic steroid treatment.
• Subject has received prior treatment with anti-B7-H4 antibody and/or anti-4-1BB antibody.