This is a first in human, open-label, dose escalation and expansion Phase I study of SIM1811-03 in adult patients with advanced tumors. SIM1811-03 is a first-in-class IgG1-based humanized anti-tumor necrosis factor type 2 receptor (TNFR2) monoclonal antibody for the treatment of malignant tumors.

This is a phase I trial to evaluate the safety, efficacy, and pharmacokinetic/ pharmacodynamic characteristics of SIM1811-03 in participants with advanced tumors.

The trial is composed of two parts, Part I and Part II. Part I is a dose escalation part to determine the MTD and/or RD of SIM1811-03 or SIM1811-03 in combination with Sintilimab Injection . Part II is a dose expansion part at RD level SIM1811-03 determined in Part I to assess the anti-tumor activity of SIM1811-03 or SIM1811-03 in combination with Sintilimab Injection in participants with advanced solid tumors or CTCL. The tumor types in Part II will be adjusted based on the response observed in Part I.

Key Inclusion Criteria:

1. Written informed consent must be obtained prior to any procedures that are not considered standard of care.
2. ≥18 years old on the day of signing informed consent, male or female;
3. Histologically and/or cytologically documented advanced/metastatic solid tumors or histologically confirmed CTCL;
4. Have relapsed or refractory advanced solid tumors or CTCL, whose disease has progressed during or after standard therapy
5. At least one measurable tumor lesion (RECIST 1.1) for participants with solid tumors. Tumor lesions previously treated with radiotherapy or local therapy should not be considered as measurable unless progression is documented.
6. Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1
7. Life expectancy of ≥ 12 weeks.
8. Adequate organ and marrow functions 9） Provide archived or fresh biopsy tumor tissue samples or tissue sections

10) Females of childbearing potential require strict contraception during the study.

Exclusion Criteria:

1) Participated in an interventional clinical trial or has used investigational devices within 28 days prior to first dose of study drug or received systemic anti-cancer treatments.

2）Toxicity due to previous antineoplastic therapy has not recovered to grade 0 or 1 unless such AEs are not considered to pose safety risks.

3) Required use of corticosteroids for more than 7 consecutive days within 14 days prior to the first dose of study treatment.

4) Participated with active or history of or risk of autoimmune disease 5) Major surgery (except biopsy) or unhealed wound within 4 weeks prior to first dose of study drug.

6) Other known malignancies within 2 years prior to enrollment. 7) Has known active central nervous system (CNS) metastases. 8) History of interstitial lung disease, drug-induced interstitial lung disease, radiation pneumonitis, symptomatic interstitial lung disease or evidence of active pneumonia that is not considered appropriate by the investigator.

9) Participants with a history of active pulmonary tuberculosis infection within 1 year prior to first dose of study drug.

10) History of hemorrhagic disease requiring transfusion within the last 3 months.