XT-150 safety and efficacy in severe osteoarthritic pain.

XT-150-1-0201 Extension: Evaluation of Safety, Tolerability, and Efficacy of XT-150 for the Treatment of Osteoarthritic Pain.

Participants in this study will have been enrolled in the 0201 study and qualify for an intra-articular injection of XT-150 into the osteoarthritic knee.

The study will assess XT-150 safety, tolerability, and efficacy in participants who received placebo in the 0201 study, or have a second qualifying knee, or a second injection into the same knee that was treated in 0201.

Inclusion Criteria:

1. Qualified and participated in clinical study XT-150-1-0201.

   1. Participant was assigned to placebo, or
   2. Participant elects to have XT-150 administered to the XT-150-untreated knee that qualified under XT-150-1-0201 criteria, or
   3. Participant had inadequate pain relief and elects to receive a second injection to the same knee treated on clinical study XT-150-1-0201

2. Sufficiently severe OA of knee to require/have recommended knee replacement surgery or be unsuitable for knee replacement surgery based on co-morbidities or orthopedic considerations; be free of local or intra-articular infection.

3. Symptomatic disease because of osteoarthritis, defined as a Verbal Numerical Rating Scale (VNRS) scores of a worst pain of at least 7 at any time during the preceding week (based on scale of 0 to 10, with 10 representing "pain as bad as you can imagine").

4. Stable analgesic regimen during the 4 weeks prior to enrollment.

5. Inadequate pain relief (minimum ≥ 5 mean on Brief Pain Inventory-Severity Scale) lasting more than 3 months.

6. In the judgment of the Investigator, acceptable general medical condition

7. Life expectancy >6 months

8. Male participants who are heterosexually active and not surgically sterile must agree to use effective contraception, including abstinence, for the duration of the study and for 3 months after the study is completed.

9. Have suitable knee joint anatomy for intra-articular injection

10. Willing and able to return for the follow-up (FU) visits

11. Able to reliably provide pain assessment

12. Able to read and understand study instructions, and willing and able to comply with all study procedures

Exclusion Criteria:

1. Hypersensitivity, allergy, or significant reaction to any ingredient of the study drug, including double-stranded DNA, mannose, and sucrose
2. Scheduled knee replacement within 4 months; participant agrees not to schedule a knee replacement appointment within 4 months of study treatment
3. History of rheumatoid arthritis of the knee or gout.
4. High peri-operative risks which in the judgment of the investigator preclude a safe knee injection procedure (e.g., poorly controlled diabetes, cardiac inadequacy such as NYHA class > II, G4 glomerular filtration rate [eGFR < 30 mL/min by Cockcroft-Gault])
5. Current treatment with immunosuppressive (systemic corticosteroid therapy [equivalent to >10mg/day prednisone] or other strong immunosuppressant)
6. History of immunosuppressive therapy; high-potency systemic steroids in the last 3 months.
7. Currently receiving systemic chemotherapy or radiation therapy for malignancy
8. Clinically significant hepatic disease as indicated by clinical laboratory results ≥3 times the upper limit of normal for any liver function test (e.g., aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase)
9. Severe anemia (Grade 3; hemoglobin <8.0 g/dL, <4.9 mmol/L, <80 g/L; transfusion indicated), uncontrolled coagulopathy (Grade 1, prolonged activated partial prothrombin time (aPTT) > upper limit of normal (ULN) to 1.5xULN), or bleeding diathesis, Grade 1 white cell counts (lymphocytes \