A Study of KD6005 in Healthy Participants and Participants With Rheumatoid Arthritis (RA)

Inclusion Criteria: Main Inclusion Criteria for Healthy Participants (Phase 1a):

1. Being voluntary to sign the informed consent form.
2. Male or female age 18 to 50 years. Have a body mass index (BMI) between 19 and 26kg/m2 inclusive and weigh at least 50kg for male , or at least 45kg female. In goodoverall health at the time of screening. Main Inclusion Criteria for RA participants (Phase 1b):
3. Being voluntary to sign the informed consent form.
4. Age 18-70 years old, and subjects with rheumatoid arthritis (RA) diagnosed by the 1987or 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria.

Exclusion Criteria: Main Exclusion Criteria for Healthy Participants (Phase 1a):

1. Known to be allergic to KD6005 or its components.
2. History of malignancy under study within 5 years, except adequately treated and curedbasal or squamous cell carcinoma of the skin or cervical carcinoma in situ.
3. Subjects who had undergone any surgical procedures within 3 months prior to screening,or will plan surgery during the study period and within 1 month after the study ended.
4. History of clinically significant cardiovascular, hepatic, neurological, respiratory,hematological, digestive, rheumatological, immune, renal, or psychiatric disordersthat the investigator believes may confuse the study results or place the subject atundue risk.
5. Subjects who are judged by the investigator to have a disease affecting drugabsorption, distribution, metabolism, and excretion; Or skin disease or other diseaseaffecting subcutaneous injection.
6. Clinical symptoms, signs, laboratory tests or X-ray tests suggest activetuberculosis(TB).
7. An infection that the investigators determined to be clinically significant occurredwithin 3 months prior to screening.
8. Blood donation within the last 3 months (more than 400mL).
9. Subjects who have participated in clinical trials of any drug or medical device within 3 months or 5 drug half-lives (whichever is longer) prior to screening.
10. Any acute illness that the investigators determined to be clinically significantoccurred in the 1 month prior to screening.
11. A history of severe herpes virus infection.
12. A history of drug use or substance abuse.
13. Subjects who received live/attenuated vaccine within 2 months prior to screening orrequired live vaccines during study participation, including within 28 days after thelast KD6005 administration.
14. Received any medication within 4 weeks prior to use of KD6005.
15. Subjects who have been tested positive for the following tests: Hepatitis B virus (HBV), Hepatitis C virus (HCV), human immunodeficiency virus (HIV).
16. Pregnant or breastfeeding females.
17. Smoke greater than 5 cigarettes/day.
18. Alcoholism: Positive breath test for alcohol.
19. Subjects who may not be able to complete the study for other reasons or who theinvestigator believes should not be included. Main Exclusion Criteria for RA participants (Phase 1b):
20. History of congestive heart failure, including asymptomatic congestive heart failure.
21. History of serious diseases of hepatic, renal and other important organs,hematological and endocrine system disorders.
22. Subjects diagnosed with other rheumatic immune system diseases, except rheumatoidarthritis secondary sjogren's syndrome and asymptomatic Hashimoto thyroiditis.
23. Severe infection or acute or chronic infection in the 6 months prior to the initialstudy.
24. History of latent or active granulomatous infection in the 6 months prior toscreening.
25. History of a non-tuberculous mycobacterium infection or an opportunistic infectionwithin 6 months prior to screening.
26. Present or previous history of malignant tumor.
27. Pregnant or breastfeeding females.
28. Subjects who have participated in clinical trials of any drug within 3 months prior toscreening.
29. Subjects who received live vaccine within 3 months prior to screening, or who willplan to receive live vaccine within 3 months from the first administration to the lastadministration of the KD6005.
30. Treatment with small-molecule targeted drugs, such as JAK inhibitors, within 4 weeksprior to randomization.
31. HBV screening includes HbsAg (surface antigen), anti-HBs (surface antibody) andanti-HBc (core antibody). Evidence of hepatitis B infection (positive for HBsAg).
32. Subjects with a positive test for tuberculosis (TB).
33. Subjects who have been tested positive for the following tests: Hepatitis C virus (HCV), human immunodeficiency virus (HIV).
34. Known to be allergic to the KD6005.
35. Subjects with a joint functional class IV or those who are bedridden orwheelchair-bound for a long time.
36. Subjects with arthritic diseases other than osteoarthritis.
37. Subjects have depression or the significant suicide ideation.