Inclusion Criteria (Part A):
- Participants who fully understand the purpose, nature, method, and potential adverse reactions of the study and voluntarily sign the informed consent form (ICF) and agree to participate.
- Healthy male or female participants; 18 to 55 years of age (both inclusive) on the day of signing ICF; meet the body mass index (BMI) criteria.
- Based on the investigator assessment, there are no abnormal findings or findings with clinical significance from the medical history consultation, physical examination, vital signs assessment, clinical laboratory tests, and 12-lead ECG.
- Female participants of childbearing potential or male participants agree to use highly effective contraception during the study.
- Participants who are willing and able to comply with the prescribed protocol treatment and evaluations
Inclusion Criteria (Part B):
- Participants who fully understand the purpose, nature, method, and potential adverse reactions of the study and voluntarily sign the informed consent form (ICF) and agree to participate.
- Participants who are willing and able to comply with the prescribed protocol treatment and evaluations.
- Male or female participants, 18 to 70 years of age (both inclusive) on the day of signing ICF.
- Currently receiving a stable SLE/CLE treatment regimen of any medication for a period of at least 1 month prior to randomization.
For SLE： 4. Meet the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) 2019 classification criteria for SLE.
5. History or presence at Screening of positive antinuclear antibodies (ANA) or anti-double-stranded DNA (anti-dsDNA) antibodies.
6. At screening have active lupus skin disease defined by the SELENA-SLEDAI at screening and randomization.
For CLE： 8. Must have diagnosis of CLE that has been histologically confirmed, with or without systemic LE manifestations.
9.Must have active CLE despite an adequate trial of conventional therapies.
Exclusion Criteria (Part A):
- Evidence or history of clinically significant diseases.
- History of herpes zoster (shingles) or recurrent herpes simplex (e.g., oral cold sores or gen-ital sores).
- Any active or suspected bacterial, viral, fungal, or parasitic infection within 30 days prior to dosing.
- History of sensitivity to any ingredients of DB-2304.
- Participants who have undergone surgery within the past 3 months or have plans for sur-gery during the study.
Exclusion Criteria (Part B):
- Have active lupus nephritis or moderate-to-severe or chronic kidney disease
- Have active neuropsychiatric SLE within 8 weeks prior to screening
- Any active skin conditions or active arthritis other than SLE that may interfere with skin or arthritis assessments (e.g., psoriasis, non-LE skin lesions, non-LE alopecia areata, drug-induced lupus, rheumatoid arthritis) at screening.
- History of, or ongoing, malignant disease, including solid tumors and hematologic malignancies with the exception of basal cell carcinomas and squamous cell carcinomas and carcinoma in situ of the cervix that have been completely excised and considered cured >2 years prior to Screening.
- Known history of a primary immunodeficiency (e.g., common variable immunodeficiency syndrome), splenectomy, or any underlying condition that predisposes the participant to infection.
NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.