Recombinant Human Thymosin Beta 4 for Injection(NL005) for Acute Myocardial Infarction

Inclusion Criteria: * Willing and able to provide written informed consent (by the participant or legally authorized representative) * Aged 18 to 75 years old, any sex * Diagnosis of ST-segment elevation myocardial infarction (STEMI) with electrocardiogram (ECG) meeting protocol-specified ST-elevation criteria, and scheduled to undergo primary percutaneous coronary intervention (PCI) * OR, regardless of ECG criteria, the participant has a completely or nearly completely blocked (TIMI flow grade 0 or 1) proximal or mid left anterior descending (LAD) coronary artery as the single culprit vessel * The blocked LAD artery has no visible collateral blood supply from other coronary arteries (Rentrop grade 0) * Total myocardial ischemic time (time from chest pain onset to guidewire passage during PCI) meets one of the following: 1. More than 2 hours and less than 6 hours of ischemic time, with either post-PCI LAD TIMI flow grade of 2 or less, or left ventricular ejection fraction (LVEF) of 50% or lower measured by cardiac ultrasound during PCI hospitalization; 2. Between 6 and 24 hours of ischemic time (inclusive) * Males and females of childbearing potential must agree to use adequate contraception (such as hormonal or barrier methods, or abstinence) throughout the study Exclusion Criteria: * Prior history of acute myocardial infarction, chronic total coronary occlusion, coronary thrombolysis, PCI, or coronary artery bypass graft surgery * Diagnosis of severe acute heart failure (Killip class III or higher) or chronic heart failure (NYHA functional class III or higher) * Severe, uncontrolled arrhythmia that cannot be corrected * Presence of aortic dissection * Severe liver or kidney dysfunction * History of stroke within the past 6 months * Current or past diagnosis of any malignancy * Blood pressure that remains at or above 180 mmHg systolic and/or 110 mmHg diastolic despite adequate antihypertensive treatment * History of clinically significant allergic reaction, especially known allergy to protein or biologic drugs * Participation in another clinical study within 3 months before screening * Unable to undergo cardiac magnetic resonance (CMR) imaging (e.g., due to implanted metal devices, severe claustrophobia, or other contraindications) * Any other condition that the investigator believes makes participation unsuitable (for example, the need for urgent or planned revascularization of non-LAD coronary arteries within 3 months)