This is a Phase 1 study to evaluate the safety, tolerability, PK, and preliminary efficacy of IO-108 monotherapy and in combination with anti-PD-1 monoclonal antibody pembrolizumab or tislelizumab in adult patients with advanced solid tumors. The study will be conducted in 3 parts, including Part A IO-108 monotherapy dose confirmation; Part B IO-108 + anti-PD-1 dose confirmation, and Part C dose expansion.

Inclusion Criteria:

1. Age ≥18, and < 75.

2. Part A and Part B Cohort 1: Patients must have histologically or cytologically confirmed advanced or metastatic solid tumor and have failed, or have been intolerant for standard systemic therapy, or for whom no treatment known to confer clinical benefit exists.

   Part B Cohort 2 and Part C: Patient with advanced or metastatic solid tumor who meet the specific criteria.

3. Patients have at least 1 measurable disease per RECIST v1.1 as assessed by local clinical site.

4. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 1.

5. Patients must have adequate hematologic function, hepatic function and renal function.

Exclusion Criteria:

1. Patients who previously received a monoclonal antibody therapy targeting LILRB2/ILT4 (including IO-108).
2. Patients who received chemotherapy, radiotherapy, biologic therapy, targeted therapy, immunotherapy, or other investigational anti-cancer therapy < 4 weeks prior to their first day of study drug administration.
3. Requires systemic corticosteroids at a dose of >10 mg daily of prednisone or the dose equivalent to other systemic corticosteroid, or other immunosuppressive agents ≤ 14 days prior to the first dose.
4. History of radiation pneumonitis, non-infectious pneumonitis or interstitial lung disease expect for radioactive pulmonary fibrosis not requiring corticosteroid treatment.
5. Symptomatic central nervous system (CNS) metastases. Note: Other protocol defined Inclusion/Exclusion criteria may apply.