Inclusion Criteria:
1. Male or female adult ≥ 18 and ≤ 45 years old at the time of signing the ICF,
2. Diagnosed with hypertrophic scars, with all the following characteristics:
1. Linear hypertrophic scar, with a width of 0.3-1.0 cm and a length of ≥10 cm;
2. Scars with any of the following characteristics: redness or purpleness, stiffness, rough surface, significant swelling, visible dilated capillaries on the surface, and possibly accompanied by pain or itching;
3. The course of the disease is 6 to 24 months (inclusive);
4. Scars are not located on the face, front of the neck, feet, hands, knees, elbows or any joints;
3. The examination during the screening period must meet the following criteria: medical history, physical examination (excluding hypertrophic scar), 12-lead ECG, vital signs, laboratory examinations are judged by the investigator to meet the requirements, and no clinically significant abnormalities were observed;
4. Subjects of childbearing potential (male or female) must take effective medical contraceptive measures during the study and within 6 months after the end of administration;
5. Subjects voluntarily participate in this clinical trial and sign the ICF, can understand and comply with the study procedures, and complete the entire study as specified by the protocol.
Exclusion Criteria:
1. Diagnosed with keloid or burn scar;
2. Positive in hepatitis B surface antigen, hepatitis C antibody, human immunodeficiency virus (HIV), or syphilis antibody tests;
3. Medication history of corticosteroids use (including inhaled steroids, triamcinolone acetonide, etc.) and COX-2 inhibitors within 3 months before the first injection of the study (if 5 times the half-life is longer than 3 months, then 5 times the half-life will prevail);
4. Impaired immune function (such as cancer, or other diseases that affect the basic immune responses);
5. Concomitant diseases that is uncontrolled or poorly controlled or may affect the study, including clinically important cardiovascular, lung, kidney, endocrine, liver, nerve, mental, immune, gastrointestinal, blood, urogenital, skeletal or metabolic disorders at the investigator's discretion;
6. Known to be allergic to STP705 or any components of its prescription;
7. Having difficulty in venous blood collection, or having a history of needle fainting or blood fainting;
8. Infection or trauma in the site to be treated;
9. Pregnant and lactating women;
10. Participated in other clinical studies and received treatment within 3 months before the first injection;
11. Blood donation or blood loss ≥400 mL within 3 months before the first injection (except for female blood loss during menstrual period), or planning to donate blood or blood components during the study period or within 3 months after the end of the study;
12. History of drug abuse/dependence or drug history or positive in drug abuse screening (screening items can include: morphine, tetrahydrocannabinol acid, methamphetamine, methylenedioxy methanphetamine, ketamine and cocaine) within 1 year before the first injection;
13. Medication history of any drugs (including prescription drugs, over-the-counter drugs, Chinese herbal medicines, etc.) or health care products within 14 days before the first injection;
14. Vaccinated with live vaccines within 4 weeks before the first injection or planning to receive live vaccines within 4 weeks after the last dose. Live vaccines include but not limited to: measles, mumps, rubella, chickenpox, yellow fever, rabies, Bacillus Calmette-Guerin, typhoid fever, COVID-19 live vaccines, etc.;
15. Any surgical, medical or laboratory pathophysiological conditions that may interfere with the safety, distribution, metabolism or excretion of the investigational drug at the discretion of the investigator;
16. Unable to communicate or cooperate with medical staff due to neurological, mental disorders or language/ verbal communication issues;
17. Other situations not suitable for participation in the study as judged by the investigator.
