This is a phase I, First-in-Human (FIH), open-label study to evaluate the safety, tolerability, pharmacokinetic (PK) profile, and preliminary efficacy of AB248 as monotherapy OR in combination with pembrolizumab in adult participants with locally advanced or metastatic solid tumors. The study will consist of a dose escalation and a dose expansion stage.

Inclusion Criteria:

• Age ≥18 years of age at the time consent is signed.
• Has adequate end organ function per laboratory testing.
• Pregnancy prevention requirements
• Has measurable disease per RECIST 1.1 as assessed by the local site Investigator/radiology.
• Has a performance status of 0 or 1 on Eastern Cooperative Oncology Group scale.
• Histologic documentation of incurable, locally advanced or metastatic tumor of the type being evaluated in individual cohorts

Exclusion Criteria:

• Has a diagnosis of immunodeficiency.
• Has a history of a previous, additional malignancy, unless potentially curative treatment has been completed, with no evidence of malignancy for 5 years.
• Has known active CNS metastases and/or carcinomatous meningitis.
• Has an active autoimmune disease that has required systemic treatment in the past 2 years.
• Has an active infection requiring systemic therapy.
• Inability to comply with study and follow-up procedures.
• Has had a severe hypersensitivity reaction (Grade ≥3) to treatment with pembrolizumab, another monoclonal antibody, or has history of any hypersensitivity to any components of the study treatments or any of their excipients.
• Has received prior systemic anticancer therapy including investigational agents within 4 weeks (or, if shorter, within 5 half-lives for kinase inhibitors) prior to first dose of study treatment.
• Has received prior radiotherapy within 2 weeks of start of study treatment or has had a history of radiation pneumonitis.
• Receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior the first dose of study treatment.
• Has received previous treatment with another agent targeting the IL-2, IL-7, or IL-15 receptors.
• Is expected to require any other form of antineoplastic therapy while on study