This is a multicenter, open-label extension (OLE) study of MHB018A in subjects with moderate-to-severe TED.

The primary objective of this study is to evaluate the improvement in proptosis from baseline (defined as the most recent measurement prior to the first dose in this study) following treatment with MHB018A Injection in subjects with active or chronic TED who previously received placebo in either the MHB018A-P-301 or MHB018A-P-302 studies, and the safety and tolerability of MHB018A Injection in TED subjects.

Inclusion Criteria:

1. Subjects voluntarily participating in the study and signing the informed consent form;

2. Aged 18-75 years (inclusive), of any gender;

3. Completed the 24-week double-blind treatment period in either the MHB018A-P-301 or MHB018A-P-302 study, and within 28 days after Week 24 visit of the previous study when enrolled in this OLE study (does not apply to subjects who meet the relapse criteria during the safety follow-up period).

4. Proptosis non-responder at Week 24 visit in the double-blind treatment period of either the MHB018A-P-301 or MHB018A-P-302 study (defined as a <2 mm reduction from baseline in the study eye, or a ≥2 mm reduction in the study eye accompanied by a ≥2 mm worsening from baseline in proptosis of the fellow eye), and/or who meet the retreatment criteria for relapse during the safety follow-up period.

5. Does not require immediate surgical ophthalmological intervention, and no corrective surgery/orbital radiotherapy is planned during the study.

6. Diabetic subjects must have well-controlled stable disease.

7. Sufficient bone marrow and organ function.

8. Eligible subjects of childbearing potential (male and female) must agree to use reliable contraceptive methods; female subjects of childbearing potential must have a negative blood pregnancy test within 7 days before the first use of the study drug and must not be breastfeeding.

9. Subject is willing and able to comply with the prescribed treatment protocol and evaluations for the duration of the study.

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Exclusion Criteria:

1. Decreased best corrected visual acuity due to optic neuropathy as defined by a decrease in vision within the last 6 months of two lines of Snellen chart, new visual field defect or color defect secondary to optic nerve involvement.

2. Corneal decompensation unresponsive to medical management.

3. Free thyroxine (FT4) and free triiodothyronine (FT3) levels <50% above or below the normal reference range at screening.

4. Received any treatment for TED, intravenous corticosteroids, immunosuppressive agents, investigational drug from the last visit of the MHB018A-P-301 or MHB018A-P-302 trial until participation in this study.

5. Identified pre-existing ophthalmic disease that would preclude study participation or complicate interpretation of the study results.

6. Acute cardiovascular disease history or treatment within 6 months before the first dose from the last visit of the MHB018A-P-301 or MHB018A-P-302 trial until participation in this study.

7. Presence of poorly controlled hypertension with systolic blood pressure ≥ 160 mmHg or diastolic blood pressure ≥ 100 mmHg; Renal artery stenosis.

8. Pregnant or lactating women.

9. Tinnitus or other hearing impairment.

10. Poor compliance or severe systemic disease history or other reasons that make the subject unsuitable for participation in this clinical study.

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