A Study of HFB200301 as a Single Agent and in Combination With Tislelizumab in Adult Patients With Advanced Solid Tumors

Inclusion Criteria: * Previously received the following lines of systemic therapy for the advanced/metastatic disease: * Gastric cancer: at least 2 lines of therapy * Renal cell carcinoma: at least 2 lines of therapy * Melanoma: * BRAF V600E mutant: must have received at least 2 lines of therapy * BRAF V600E wild type: must have received at least 1 line of therapy * Sarcoma: at least 1 line of therapy * Testicular germ cell tumor: at least 2 lines of therapy * Cervical cancer: at least 2 lines of therapy * Mesothelioma: at least 2 lines of therapy * Non-small cell lung cancer: at least 2 lines of therapy * Head and neck squamous cell carcinoma: at least 2 lines of therapy * Suitable site to biopsy at pre-treatment and on-treatment * Measurable disease as determined by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 or modified RECIST (mRECIST) for mesothelioma * Eastern Cooperative Oncology Group performance status of 0 or 1 Exclusion Criteria: * Systemic anti-cancer therapy within 2 weeks prior to start of study drug or within 4 weeks for immune-oncologic therapy * For soft tissue sarcoma and testicular germ cell tumor patients only: prior immune therapy * Therapeutic radiation therapy within the past 2 weeks * Prior exposure to agents targeting the Tumor Necrosis Factor Receptor type 2 (TNFR2) receptor * Active autoimmune disease requiring systemic treatment in the previous 2 years * Systemic steroid therapy (\>10 mg/day of prednisone or equivalent) or any immune suppressive therapy ≤ 14 days before first dose * Persisting toxicity of ≥Grade 2 (≥Grade 1 for diarrhea) relating to prior anti cancer therapy with the following exceptions: * All grades of alopecia are acceptable * Endocrine dysfunction on replacement therapy is acceptable * Severe or unstable medical condition, including uncontrolled diabetes, coagulopathy, or unstable psychiatric condition * Major surgery within 4 weeks of the first dose of study drug * History or presence of drug or non-drug induced interstitial lung disease or pneumonitis ≥Grade 2. For combination only: non-small cell lung cancer patients, mesothelioma or patients with significantly impaired pulmonary function or who require supplemental oxygen at baseline must undergo an assessment of pulmonary function at screening * History of allergic reactions, immune related reactions, or cytokine release syndrome (CRS) attributed to compounds of similar chemical or biologic composition to monoclonal antibodies or any excipient of HFB200301 * Using sensitive substrates of major cytochrome P450 (CYP450) enzymes * Known active malignancy, with the exception of the specific cancer under investigation in this trial, that required treatment within the previous 2 years * For combination only: * Prior randomization in a tislelizumab study regardless of the treatment arm, until the primary and key secondary endpoints of the study have read out * Hypersensitivity to tislelizumab or any of its excipients.