The goal of this phase IIc clinical trial is to learn if recombinant human thymosin beta 4 injection (NL005) works to treat heart damage in people who have had a serious type of heart attack called ST-segment elevation myocardial infarction (STEMI) and have been treated with emergency percutaneous coronary intervention (PCI, a procedure to open the blocked artery). It will also learn about the safety of NL005. The main questions it aims to answer are:
* Does NL005 lower the size of permanent heart muscle damage measured by cardiac magnetic resonance (CMR) scan 90 days after treatment? * What medical problems do participants have when taking NL005?
Researchers will compare two different doses of NL005 to a placebo (a look-alike substance that contains no drug) to see if NL005 works better to reduce heart damage caused by the heart attack.
Participants will:
* Receive NL005 or placebo through a vein within 4 hours after the PCI procedure, then once a day for 7 days * Stay in the hospital for the first week for monitoring, blood draws, and electrocardiograms (heart tracings) * Have a CMR scan on Day 6 and Day 90 to measure the size of the heart injury * Return to the hospital for checkups on Day 30 and Day 90 * Be contacted by the study team (by phone or online) 3 times during the first year and come back to the hospital on Day 360 to check long-term recovery
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
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