This is a Study to Evaluate the Safety and Tolerability of ABL503, and to Determine the Maximum Tolerated Dose (MTD) and Recommended Phase 2 Dose (RP2D) of ABL503 in Subjects with Any Progressive Locally Advanced or Metastatic Solid Tumors

Inclusion Criteria:

• Histologically and/or cytologically confirmed diagnosis of any progressive locallyadvanced (unresectable) or metastatic solid tumors that have relapsed or arerefractory following the last line of treatment, for which prior standard therapyhas been ineffective, standard therapy does not exist, or is not consideredappropriate.

• With AE(s) excluding alopecia or Grade 2 toxicities that are deemed stable orirreversible (eg, peripheral neuropathy) from prior therapy that have improved toGrade 1 or the baseline grade more than 14 days prior to the first administration ofthe study drug

• Adequate hematologic, hepatic, and renal functions confirmed based on the screeninglaboratory tests and reconfirmed with additional safety laboratory tests performedwithin 72 hours prior to the first administration of ABL503

Exclusion Criteria:

• Prior anticancer monoclonal antibody treatment or investigational therapy within 28days prior to the first administration of study drug or has not recovered (ie, ≤Grade 1 or at baseline grade) from AEs due to previously administered agent morethan 14 days prior to ABL503 administration

• Prior chemotherapy or radiation therapy within 2 weeks or targeted small moleculetherapy within 5 half-lives prior to the first administration of study drug or hasnot recovered (ie, ≤ Grade 1 or at baseline grade) from AEs due to previouslyadministered agent more than 14 days prior to ABL503 administration

• Requiring or received systemic steroid therapy or any other immunosuppressivetherapy within 14 days prior to study drug administration.

• Risk factors for bowel obstruction or bowel perforation (including but not limitedto a history of acute diverticulitis, intra-abdominal abscess, and abdominalcarcinomatosis.

• Discontinued from prior immunomodulatory therapy due to any intolerableimmune-related adverse events (IrAEs) requiring systemic steroid treatment

• History of drug-induced pneumonitis (interstitial lung disease) or currently haspneumonitis

• Received prior treatment with an anti-4-1BB antibody