The goal of this clinical trial is to evaluate the safety and tolerability of multiple doses of human umbilical cord mesenchymal stem cell injection in patients with Ankylosing Spondylitis, and to further explore the efficacy, pharmacodynamic profile and appropriate dose of administration to provide a basis for the use of safer and more effective treatments for patients with Ankylosing Spondylitis in the future.

Participants are required to sign an informed consent form and, after undergoing a series of tests and meeting the protocol's entry and exclusion criteria, are assigned to a dose group for intravenous infusion of human umbilical cord mesenchymal stem cells.

Ankylosing spondylitis (AS) is an inflammatory disease of unknown origin that mainly affects the sacroiliac joints, spinal prominences, paraspinal soft tissues and peripheral joints, and may be accompanied by extra-articular manifestations, and in severe cases, spinal deformities and ankylosis. The etiology of AS is still unclear, but epidemiology shows a strong association with genetic and environmental factors. Treatment is aimed at relieving signs and symptoms, restoring physical function, preventing joint damage, improving quality of life, and preventing complications of spinal disorders. Treatment methods include patient education such as physical exercise and proper posture in life and sleep; pharmacological treatment such as non-steroidal anti-inflammatory drugs (NSAIDs), biologics (e.g. TNF-α antagonists, IL-17 antagonists), DMARDs (e.g. salbutamol, methotrexate), glucocorticoids, etc. In addition, surgical methods such as total hip arthroplasty are also available. Despite these therapeutic or disease control methods, none of them can stop the radiological progression of AS, restore the structural damage of patients, or achieve a cure for the disease.

Stem cells are undifferentiated cells that exist in embryonic or adult tissues and have the potential for self-renewal replication and multidirectional differentiation. Mesenchymal stem cells (MSCs) are one of the most used stem cells in basic and clinical research. According to the literature, MSCs have the ability to migrate and nest in diseased and damaged tissues in vivo, and repair damaged tissues through their multidirectional differentiation potential. MSCs can also improve the local microenvironment, support and promote the regeneration and differentiation of endogenous stem cells, exert anti-inflammatory effects and regulate immunity through their paracrine mechanisms. The collection of human umbilical cord derived mesenchymal stem cells (hUC-MSCs) is non-invasive and there are no medical ethics issues in obtaining them.

There are no medical ethics issues in obtaining them. Similar to other tissue-derived MSCs, hUC-MSCs have a unique self-renewal capacity and multidirectional differentiation potential, such as the ability to differentiate into adipose, bone, cartilage, nerve and liver cells [6]. These properties make hUC-MSCs have the theoretical possibility to treat AS.

Currently, studies on MSCs for the treatment of ankylosing spondylitis (AS) are in the exploratory stage, and several studies have confirmed the safety and efficacy of MSCs for the treatment of AS.

The primary objective of this clinical trial was to examine the safety and tolerability of human umbilical cord MSC injection in patients with AS, and the secondary objective was to examine the initial effectiveness of human umbilical cord MSC injection in treating patients with AS. The trial was designed as a single-arm, single-dose, dose-escalation clinical trial with three dose groups: low-dose group (1,000,000 cells/kg), medium-dose group (3,000,000 cells/kg), and high-dose group (5,000,000 cells/kg). A "3+3" dose escalation design was used, with 3-6 subjects included in each dose group, sequentially from the low to the high dose group. Each subject in the high-dose group was enrolled on a case-by-case basis, and each subject in the high-dose group was allowed to enroll in subsequent subjects only after completing at least 7 days of safety observation after dosing. Each subject received only one corresponding dose.

After all subjects in each trial dose group have completed a 4-week (28-day) dose-limiting toxicity (DLT) observation period, the decision to start the next dose group will be made by the investigator and sponsor after discussion of relevant safety data. Subjects will enter the follow-up period after completing the D28 visit, and the investigator will continue to observe the safety and efficacy of the subjects after dosing.

The investigators continued to monitor the safety and efficacy of the drug after administration. If a subject experiences disease progressiona or requires other treatment (including but not limited to biologics), the investigator will determine whether the subject should be discontinued from the patient risk-benefit perspective and discharged from the group as specified; subjects discharged from the group as determined by the investigator will be followed up as specified for long-term follow-up.

Subjects who have completed the DLT observation period in the previous dose group and have confirmed that the drug is safely tolerated, the investigator and sponsor will agree on whether to proceed to the next dose group. Concurrent enrollment in 2 or more dose groups is not permitted. If during the trial a dose group is observed to meet the termination dose creep criteria, the dose escalation will be terminated and a decision to continue the study with a downward dose adjustment will be made by the investigator and sponsor. The previous dose in the dose group that reached the termination criteria was designated as the maximum tolerated dose (MTD). If the MTD has not been explored and the subject is still safely tolerated after completion of the highest dose group (5,000,000 cells/kg) preset for this trial, the decision to continue with a higher dose escalation will be made by the investigator in consultation with the sponsor.

The extent of adverse events observed in the trial will be determined by the CTCAE 5.0 grading scale, with the following The dose creep will be terminated and the investigator and sponsor will mutually agree whether to use the previous dose as the MTD for the single dose tolerance trial. MTD of the dosing tolerance test.

1. 1 DLT in 3 subjects in a dose group; 3 additional subjects will be included in that dose group for tolerance testing;
2. If ≥2 DLTs occur in 6 subjects in a dose group, the previous dose level of that dose level defined as MTD and dose escalation was stopped.

If the maximum dose group is reached and still no MTD is defined, the investigator and sponsor consult to determine if continued creep.

Inclusion Criteria:

• A definitive diagnosis of ankylosing spondylitis (AS) (according to the 1984 New York Revised Criteria, Annex 1) with active AS. Active AS is defined as a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score of ≥4. Active AS is defined as a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score of ≥4;
• Received at least 2 non-steroidal anti-inflammatory drugs (NSAIDs) for a total of 4 weeks or more prior to screening. Patients who received at least 2 NSAIDs for a total of 4 weeks or more without significant improvement in symptoms as evaluated by the investigator or who were intolerant; if Patients receiving salazosulfapyridine and/or methotrexate should have been on treatment for at least 3 months or longer and on a stable dose for at least 4 weeks or more prior to enrollment. If the patient is receiving salazosulfapyridine and/or methotrexate, the length of treatment prior to enrollment should be at least 3 months and longer and the stable dose at least 4 weeks and longer;
• If the patient is receiving glucocorticosteroid therapy, stabilization for at least 4 weeks prior to enrollment to a dose equivalent to ≤ 10 mg of prednisone/day;
• Patients and spouses who do not plan to have children within 1 week prior to screening and within 6 months after the end of the trial and who agree to to use effective non-pharmacological contraception during the trial;
• Patients voluntarily signed an informed consent form and were willing to cooperate with the trial process.

Note: CT findings may be accepted if the diagnosis is not clear on x-ray.

Exclusion Criteria:

• Those with complete spinal rigidity;
• Those with hypersensitivity to known components of the test drug, or a history of severe allergy.
• Persons with a history of any malignancy (except basal cell carcinoma of the skin, carcinoma in situ) within 5 years prior to dosing
• Persons with a cardiovascular or cerebrovascular event (heart attack, ischemic or hemorrhagic stroke (except lacunar cerebral infarction), severe cardiac arrhythmia, deep vein thrombosis, etc.) within 3 months prior to dosing
• Those who have had a serious infection or have an active infection requiring intravenous antibiotic treatment within 4 weeks prior to screening
• Lactating females or females with positive blood pregnancy test results at screening/baseline
• Persons with known human immunodeficiency virus infection or impaired immune function or infectious disease (e.g. HBsAg positive, HBcAb positive with HBV-DNA titer > 1000 IU/ml, HCV-Ab, HIV-Ab, syphilis test (TRUST), tuberculosis test (T-SPOT.TB) positive);
• Patients who have participated in other clinical trials or studies within 2 months prior to dosing;
• Those who have been treated with TNF-alpha antagonists or other biological agents within 3 months prior to dosing
• Those who have received DMARDs class drugs within 1 month prior to dosing (except for those treated with salazosulfapyridine or methotrexate for 3 months or more prior to screening and at a stable dose for at least 4 weeks or more) with leflunomide discontinuation <8 weeks; or those with discontinuation time <7 drug half-lives depending on the actual drug class (i.e. DMARDs class drug elution period should exceed 7 half-lives of the corresponding drug), whichever is longer;
• Those whose screening or baseline phase examination meets any of the following: Glutamic aminotransferase (AST) or glutamic alanine aminotransferase (ALT) > 2.5 x ULN (non-hepatic source excluded); Serum creatinine > 1.5 x ULN or glomerular filtration rate a < 60 mL/min/1.73 m2; Activated partial thromboplastin time (APTT) >1.5×ULN or prothrombin time (PT) > 2.5 x ULN (not receiving anticoagulation); Left ventricular ejection fraction ≤ 45%.
• Previously treated with stem cell therapy;
• Subjects with any other irreversible condition or symptom with an expected survival of <3 months
• Those who have undergone spinal or joint surgery within 2 months prior to dosing;
• History of alcoholism, mental illness, drug abuse, or use of any drug within 12 months prior to administration;
• Any other condition that, in the judgment of the investigator, makes them unsuitable for participation in this trial.