A Study of ES101 (PD-L1x4-1BB Bispecific Antibody) in Patients With Advanced Malignant Thoracic Tumors

Inclusion Criteria: * Ability to understand and the willingness to sign a written informed consent form. * Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1. * At least one measurable lesion is required (RECIST v1.1) * Phase 1b: Subjects with pathologically or cytologically confirmed recurrent or metastatic NSCLC without known EGFR mutation and ALK and ROS1 gene rearrangements. * Phase II: Subjects with pathologically or cytologically confirmed recurrent or metastatic malignant thoracic tumours who have received 1-2 lines of systemic anti-tumour therapy, including platinum regimens, and have failed, including at least 2 cycles of chemotherapy. Exclusion Criteria: * Prior exposure to 4-1BB agonists. * Receipt of any anticancer investigational product or any approved drug(s) or biological products (except hormone-replacement therapy, testosterone or oral contraceptives) within 4 weeks prior to the first dose of study drug. Previous exposure to oral fluorouracils or small molecular targeted drugs require a minimum washout period of 2 weeks or 5 half-lives prior to the first dose of study drug (whichever is longer). Previous exposure to mitomycin C or nitrosourea requires a minimum washout period of 6 weeks prior to the first dose of study drug. * Receipt of PD-L1 therapy within 24 weeks prior to the first dose of study drug. * Known allergies to CHO-produced antibodies, which in the opinion of the Investigator suggests an increased potential for an adverse hypersensitivity to ES101. * Grade ≥ 3 immune-related adverse events (irAEs) or irAE that lead to discontinuation of prior immunotherapy. Some exceptions as defined per protocol apply. * Subject has not recovered from all AEs of previous anticancer therapies to baseline or ≤ Grade 1 per CTCAE v5.0 before teh first dose of study drug. Certain exceptions as defined in protocol apply. * Active autoimmune disease or documented history of autoimmune disease that required systemic steroids or other immunosuppressive medications. Certain exceptions as defined in protocol apply. * Active interstitial lung disease (ILD) or pneumonitis or a history of ILD or pneumonitis requiring treatment with steroids or other immunosuppressive medications. * Systemic anti-infectious drug treatments within 4 weeks prior to the first dose of study drug. * Pregnant or nursing females.