This is a Phase 1 trial. The overall objective is to evaluate the safety and potential efficacy effect of specific type of umbilical cord blood product (CFL001), which, other than specific modifications in manufacturing to render it compatible with current Good Manufacturing Practice (cGMP), is essentially similar to that reported in real-world experience.

The Phase 1 trial will enroll three subjects into an initial group receiving a low dose of CFL001. Provided that these subjects tolerate this dose well, will proceed to enroll three subjects into a group receiving a middle dose of CFL001. Provided that these subjects tolerate this dose well, will proceed to enroll three subjects into a group receiving the highest dose of CFL001.

All subjects will have Symptomatic Sacroiliac Joint (SIJ) syndrome, with clinical average pain score in the month prior to enrollment ≥50 and ≤90 on a 100-point scale.

Inclusion Criteria:

1. Age ≥ 18 years and ≤ 90 years.

2. Diagnosis of SIJ syndrome based on clinical findings, including the Fortin, FABER and compression sign.

3. Severity of Sacroiliac Joint (SIJ) syndrome with a baseline Oswestry Disability Index (ODI) score ≥ 30% and an SI joint pain score of ≥ 50 and ≤ 90 on the Visual Analogue Scale (VAS) 100 mm scale.

4. Individuals with either unilateral or bilateral SIJ arthritis can be candidates for enrollment; if both joints are deemed appropriate for administration of the test agent by all other inclusion criteria, then the SIJ which the participants reports as more painful will be treated, or if both are equally painful then we will use a random generator approach ("flip a coin") to determine which joint will be treated.

5. ≥75% decrease in pain within 2 days after image-guided injection of only local anesthetic (with no steroid) into the SIJ within 3 months prior to screening.

   OR Established SIJ condition based on decrease in pain after image-guided injection of local anesthetic and steroid into the SIJ 3 months prior to screening.

6. Body mass index < 40 kg/m2.

7. Ability to comply with the requirements of the study.

8. Ability to understand and provide written informed consent.

9. All participants of reproductive age/capacity to confirm use of adequate contraception during the study period.

10. All participants should have tried and failed conservative therapies such as medications (acetaminophen and/or NSAIDs or Tramadol); daily home exercise or home stretching, including hip-girdle and core exercise, with the target of 20 minutes; and guided physical therapy at a facility once weekly for six weeks, if logistically practical. Failure of the above conservative therapeutic approaches is defined as persistent pain after three months despite attempting the above.

Exclusion Criteria:

1. Prior radiation to the SIJ.
2. Use of any pain medication or therapy less than 15 days prior to test product administration that has not or will not have had a stable dosage, frequency, or intensity for at least 3 months prior to test agent administration. Use of scheduled pain medication other than acetaminophen for conditions unrelated to SIJ syndrome that has not had a stable dosage for at least 3 months prior to test agent administration. Unwillingness to consider avoiding the use of pain medication for at least 24 hours prior to each follow up evaluation.
3. Intra-articular treatment with corticosteroids or systemic steroid use within 3 months prior to screening.
4. Intra-articular treatment with regenerative medicines (e.g., plasma, stem cell, placental products) at any point prior to screening.
5. Participated in another clinical trial within the last 6 months.
6. An absolute value vital sign outside the following ranges: Systolic blood pressure >170 or <100, pulse rate of >100 or <50 bpm, and respiratory rate >22. Reasonable delay (i.e., one hour) may be provided at investigator's discretion to evaluate for return to acceptable parameters in the event that the subject had been subjected to a stressful circumstance prior to arrival in clinic.
7. Intra-articular treatment with hyaluronic acid within 6 months prior to screening.
8. Surgical intervention on the index SIJ < 12 months, or arthroscopy < 3 months prior to screening.
9. Non-ambulatory status.
10. Past or current diagnosis of fibromyalgia or inflammatory arthritis, gout, rheumatoid arthritis, lupus arthropathy, psoriatic arthritis, avascular necrosis, severe bone deformity, active infection of the SIJ or at the site of injection, pes anserine bursitis, neurogenic or vascular claudication, or uncontrolled diabetes mellitus (HbA1C >8%).
11. Past or current diagnosis of concurrent diseases, including uncontrolled arrhythmias, Class 3 or 4 congestive heart failure, active hepatitis B or C, liver enzymes ≥ 2 times Upper Limit of Normal (ULN) if there is also elevation of bilirubin, hypercoagulable state, estimated Glomerular Filtration Rate (eGFR) <45 mL/min by chronic kidney disease Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), and untreated malignancy or malignancy diagnosed within 6 months.
12. Poorly controlled condition anticipated to have a likelihood of steroid requirement during the course of the trial that could potentially confound the outcomes.
13. Past or current diagnosis of cancer, or at a high risk of recurrence.
14. Diagnosis of secondary arthritis due to traumatic injury in the index SIJ within 2 years of screening.
15. SIJ effusion in the index SIJ at screening that requires drainage for diagnostic purposes or symptomatic relief.
16. Clinically significant, ongoing illness or medical condition, that in the opinion of the investigator constitutes a safety risk for participation in the study or that could interfere with achieving the study objectives, conduct or evaluation.
17. Females who are pregnant or lactating.
18. Regular use of anticoagulants (daily use of aspirin < 325 mg is acceptable).
19. Active alcohol or substance abuse or any other reason that makes it unlikely that the subject will comply with study procedures.
20. Positive results on the urine drug screen for a banned substance or substance for which a subject does not have a valid prescription, using standard screen at clinical site.
21. Subjects with a psychiatric illness or condition, which, in the opinion of the investigation, would interfere with the conduct of the study or the interpretation of study results. Subjects with stable anxiety and depression defined as being on stable doses of antidepressant and anxiety drugs for the last 6 months and for which no dose changes are expected during the study can be included.
22. Clinically significant medical, surgical, psychiatric, or laboratory abnormality that, in the judgment of the investigator, is likely to adversely affect the subject's risk-benefit or interfere with study compliance or assessment of safety or efficacy.
23. Known allergy to local anesthetics or components of the study drug, including dimethylsulfoxide (DMSO)
24. Known allergy to radiographic contrast.
25. Subjects with autoimmune disease or a known history of having Acquired Immunodeficiency Syndrome (AIDS) or Human Immunodeficiency Virus (HIV).
26. Severe back pain due to other causes (e.g., lumbar disk degeneration, spinal stenosis), that in the opinion of the clinical investigator will render assessment of the SIJ pain difficult or ambiguous.
27. History of recent (<1 year) major trauma to the pelvis.
28. Metabolic bone disease (either induced or idiopathic).
29. Involvement in litigation.
30. Receiving disability payments or worker's compensation for back or SI joint pain.

This is an open-label study with nine subjects, who will all receive an intra-articular injection of the CFL test agent, at either of three dose levels (30 x 106 TNC, 60 x 106 TNC, and 90 x 106 TNC). The administration will be performed under ultrasound image guidance. The first three subjects will receive the 30 x 106 TNC dose; provided that the adverse event profile is acceptable, the next three subjects will receive the 60 x 106 TNC dose; provided that the adverse event profile remains acceptable, the next three subjects will receive the 90 x 106 TNC dose.