This is a multicenter, open-label Phase1/2 study aimed at evaluating the safety, tolerability, pharmacokinetic (PK) profile, pharmacodynamics (PD), immunogenicity, and preliminary efficacy of ESG206. The study will be conducted in patients with primary immune thrombocytopenia.

Phase 1 is a dose escalation study, and Phase 2 is an extended cohort study, subjects will be treated with ESG206.

In Phase 1&2, the study includes Screening (no more than 28 days), Treatment (14 weeks), and the post-treatment follow-up (8 weeks), for those sufferring a treatment failure, the safe follow-up will be conducted 28 days after the last dose.

And the safety, tolerability, pharmacokinetics, pharmacodynamics, immunogenicity, and preliminary efficacy of ESG206 in primary ITP will be assessed in this study.

Inclusion Criteria:

• 1. Willing and able to provide written informed consent for this trial.
• 2. Male or female, age ≥ 18 years on the day of signing the informed consent form.
• 3. Diagnosed with primary immune thrombocytopenia (ITP), and having received treatment of corticosteroids ± intravenous immunoglobulin (IVIG) in the past.
• 4. At the time of the last ITP treatment, loss of response, insufficient response, no response or intolerance occurred.
• 5. At screening, Platelet Count revealed < 30 * 10^9/L twice (with an interval of at least 24 hours between the two tests).
• 6. Subjects must have adequate organ function.
• 7. The World Health Organization (WHO) bleeding scale is 0-1.
• 8. Fertile men and women of reproductive age must agree to use effective contraception from the time they sign the informed consent until 180 days after the last dose of the trial drug. Women of reproductive age include premenopausal women and women within 2 years after menopause. Women who are fertile must have a pregnancy test within 7 days before the trial drug is first given and the result should be negative.

Exclusion Criteria:

• 1. Diagnosed with secondary immune thrombocytopenia, or there is evidence that the patient has a secondary cause of immune thrombocytopenia, or the patient has multiple immune cytopenias.
• 2. Previously received B-cell depletion therapy (e.g., rituximab, Ianalumab, etc.).
• 3. Received platelet transfusion or whole blood transfusion, plasma exchange, or any other rescue treatment within 14 days before the first administration of the trial drug.
• 4. Participated in other investigational drug clinical studies within 4 weeks before the first administration of the investigational drug or within 5 half-lives of the investigational drug received (whichever is longer).
• 5. Underwent splenectomy within 12 weeks before the first administration of the investigational drug.
• 6. Received traditional Chinese medicine treatment with definite platelet-raising effects within 1 week before the first administration of the trial drug.
• 7. Underwent major surgery within 4 weeks before the first administration of the investigational drug or needs to undergo major elective surgery during the study period.
• 8. Diagnosed with Evans syndrome or any other cytopenia (patients with mild anemia related to bleeding or iron deficiency are eligible for inclusion in the study).
• 9. Patients with current or previous life-threatening bleeding related to thrombocytopenia.
• 10. Patients with concurrent coagulation disorders and/or receiving antiplatelet or anticoagulant therapy (e.g., warfarin, clopidogrel, or new oral anticoagulants), except for low-dose acetylsalicylate (≤150 mg/day).
• 11. Patients with deep vein thrombosis or arterial thrombosis within 6 months before enrollment, and/or with risk factors for hereditary thrombophilia.
• 12. Patients with a history of severe cardiovascular and pulmonary diseases.
• 13. Patients with uncontrolled hypertension (systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg).
• 14. Patients with human immunodeficiency virus (HIV) infection, or active hepatitis B or C, or liver cirrhosis.
• 15. Patients with active viral, bacterial, or other infections requiring systemic treatment during the screening period, or with a history of clinically significant recurrent infections (e.g., bacterial infection with capsule). Patients with a history of tuberculosis (TB) or latent TB who have undergone anti-TB treatment may be eligible for inclusion.
• 16. Patients who received live or attenuated live vaccines within 4 weeks before the first administration of the investigational drug.
• 17. Patients with a history of or current malignant tumors, except for cured non-melanoma skin cancer, carcinoma in situ (e.g., cervical cancer, breast cancer, bladder cancer, prostate cancer), and cancers that have been in complete remission for at least 3 years without evidence of recurrence.
• 18. Patients with any severe and/or unstable pre-existing medical, mental, or other conditions that the investigator deems may interfere with the patient's efficacy, safety, informed consent, or compliance with the study procedures.
• 19. Patients with known immediate or delayed hypersensitivity reactions to monoclonal antibodies or components of the trial drug, or with a history of allergic constitution.
• 20. Pregnant or lactating women.
• 21. Patients who are unwilling or unable to follow the protocol procedures.