This clinical trial is designed as a Phase 1/2a clinical trial targeting patients with critical limb ischemia. The trial is composed of Phase 1 to assess the tolerability and safety and Phase 2a to assess the safety and efficacy of the investigational product(A cluster of adipose-derived mesenchymal stem cells (3D-A) (cluster of adipose- derived mesenchymal stem cells)) and proceeds in that order.

This clinical trial is designed as a Phase 1/2a clinical trial targeting patients with critical limb ischemia. The trial is composed of Phase 1 to assess the tolerability and safety and Phase 2a to assess the safety and efficacy of the investigational product.

Phase 1: Open-label, 3 + 3 design, single-center This phase is conducted in a 3 + 3 design by dose level to evaluate the tolerability of the investigational product.

If the subject voluntarily agrees signs the informed consent formin writing to participate in this clinical trial, the subjects who had necessary check-ups and tests and meet the inclusion criteria after subject conformity assessment are registered in the clinical trial.The subjects receive the investigational product once and are checked for adverse events through day 1 and then discharged. The safety and efficacy assessments are conducted through visits at week 4, week 12, and week 24 after administration.

Subjects are evaluated for adverse events up to week 4 after the administration of the investigational product by registering 3 subjects each at the dosing phase. This evaluation is conducted according to the number of persons subjects who developed Grade 3 or higher adverse drug reactions (ADRs) according to CTCAE Version_5.0 in which a causal relation with the investigational product cannot be ruled out.

If the maximum tolerated dose (MTD) is determined with the test group 2 (high dose) in the Phase 1 clinical trial, the Phase 2a clinical trial will be conducted with the two groups, test group 2 and test group 1.

However, if adverse events occur in 1 of 6 subjects, the test group 2 will be decided considered as the maximum tolerated dose (MTD), or but only the test group 1 will proceed to Phase 2a.

If adverse events occur in 2 or more subjects out of 6 subjects, a dose smaller than test group 1 (low dose) is determined to be the maximum tolerated dose. The Phase 2a clinical trial will not proceed and the clinical trial will end.

Phase 2a: Open-label, sequential assignment, single-center If tolerability and safety are secured 4 weeks after administration of the investigational product of Phase 1, Phase 2a is conducted.

Only those subjects meeting the final inclusion criteria are sequentially assigned, admitted by the same procedure, and administered the investigational product once. Subjects are checked for adverse events through day 1 and discharged. Safety and efficacy assessments are performed at week 4, week 12, and week 24 after administration. All subjects are tested with the same schedule, excluding their doses.

The subjects enrolled in Phase 1 are analyzed for efficacy through visits at week 12 and week 24 so that all subjects (Phase 1 and Phase 2a) are assessed and analyzed for efficacy.

Inclusion Criteria:

1. Adults aged 19 or older
2. A person diagnosed with critical limb ischemia due to peripheral artery stenosis or obstructive occlusive disease (Rutherford category 4, 5, 6)
3. Patients with critical limb ischemia where symptoms do not improve even after medication treatment for more than 3 months[1]
4. Persons who voluntarily agreed to participate in this clinical trial

Exclusion Criteria:

1. Persons whose life expectancy is less than 6 months

2. Patients who underwent surgery and interventional procedures (percutaneous vascular intervention, vascular reconstruction, etc.) in the same disease within 3 months of screening

3. Patients in need of interventional procedure or surgery

4. Patients with a history of administration of other cell therapy products

5. Persons who have received systemic immunosuppression treatment within 3 months of screening

6. Persons with a history of a malignant tumor within 5 years of screening (However, non-metastatic basal cell skin carcinoma, squamous cell carcinoma of the skin or carcinoma in situ of the cervix that does not recur for at least 1 year before the registration are excluded)

7. Persons with a hematologic disease with major bleeding or bleeding predisposition within 3 months of screening

8. Women who are pregnant, breastfeeding or planning to become pregnant during the clinical trial period or women of childbearing potential who do not use medically acceptable birth control

   *Medically acceptable contraception:

   • Medicine: Oral contraceptives, skin patches or progestin medications (Transplant or injection)
   • Diaphragm: Condoms, diaphragms, intrauterine devices (IUDs), vaginal suppositories
   • Abstinence: Absolute abstinence (However, periodic abstinence (e.g., calendar method, ovulation method, sympto-thermal method) and control are not considered acceptable contraceptive methods.)

9. Persons who participated in other clinical trials within 3 months of screening

10. Persons who were administered prohibited concomitant medications related to this clinical trial

11. Persons with alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels more than twice the normal upper limit at the time of screening

12. Persons identified with estimated glomerular filtration rate (eGFR) levels < 30 mL/min/1.73 m2 at the time of screening

13. Persons with a history of allergies or hypersensitivity to the investigational product or its components

14. Persons who are judged to be inadequate to participate in clinical trials by other investigators