To assess the efficacy and safety of TQH3906 in subjects with moderate to severe plaque psoriasis, as well as the PK and PD characteristics of multiple doses

Inclusion Criteria:

• Be 18-70 years old (both 18 and 70 years old), regardless of gender；
• Clinically diagnosed with stable moderate to severe plaque psoriasis with a history ≥ 6 months (from randomization), and no morphological changes in skin lesions or significant disease outbreaks as assessed by the investigator;
• Appropriate for systemic therapy or phototherapy as judged by the investigator;
• At screening and baseline, the PASI score was ≥ 12 points, the BSA ≥ 10%, and the sPGA ≥ 3 points ;
• Have a full understanding of this study, voluntarily participate in the trial, and have signed a written informed consent form;
• Subjects (including partners) are willing to voluntarily use appropriate and effective contraceptive measures from screening to 3 months after the last dose of study drug.

Exclusion Criteria:

• Pregnant and lactating females;

• Have other forms of psoriasis other than plaque psoriasis (e.g., guttate psoriasis, generalized pustular psoriasis, erythrodermic psoriasis, arthropathic psoriasis);

• Presence of serovirological abnormalities during the screening period:

  1. Active hepatitis, or hepatitis B surface antigen (HBsAg) positive, or hepatitis B core antibody (HBcA positive and Hepatitis B virus (HBV) DNA positive, or Hepatitis C virus (HCV) antibody positive and HCV-RNA positive;
  2. Positive for HIV antibody during the screening period, or have a history of HIV infection in the past;
  3. Positive Treponema pallidum antibody and positive non-Treponema pallidum serum test (RPR or TRUST) during the screening period;

• Have a history of active tuberculosis during the screening period or before, or have latent tuberculosis infection found at screening (refers to T-SPOT positive without clinical manifestations). (Note: Patients with latent tuberculosis infection can be re-screened 1 month after starting prophylaxis according to the guidelines, and in order to continue to participate in the study, patients must agree to continue to complete the prophylactic regimen during the study, but rifampicin treatment should be avoided.) ;

• Has a history of severe herpes zoster or herpes simplex infection, including but not limited to herpetic encephalitis, disseminated herpes simplex, generalized herpes zoster;

• History of severe bacterial, fungal or viral infection within 2 months prior to randomization, requiring hospitalization for intravenous antibiotics or antiviral drug treatment;

• Live vaccine within 4 weeks prior to randomization or planned live vaccine during the study;

• Clinically significant infection, including but not limited to upper respiratory tract infection, lower respiratory tract infection, herpes simplex, herpes zoster, during the screening period, and requiring antibiotic or antiviral medication treatment;

• Has any significant illness or unstable clinical condition (such as renal, hepatic, hematologic, gastrointestinal, endocrine, pulmonary, psychiatric, neurological, immune, or locally active infectious/infectious disease) that is judged by the investigator to be unsuitable for participation in this study.

• Abnormal laboratory tests during the screening period:

  1. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥ 3 times upper limit of normal (ULN);
  2. Hemoglobin <90g/L;
  3. White blood cell count< 3.0×109/L;
  4. Neutrophil count<1.0×109/L;
  5. Lymphocyte count<0.5×109/L;
  6. Platelet count < 100×109/L;
  7. Total bilirubin >2 times ULN;
  8. Other significant laboratory test abnormalities that, in the opinion of the investigator, the subject is not suitable for participation in this study.

• History of malignant tumors (including carcinoma in situ) and lymphoproliferative disorders within 5 years prior to randomization;

• Those who have received at least 6 consecutive months of anti-IL-12, IL-17, IL23 monoclonal antibody drugs (such as ustekin, secukziu, ichizzo, gusechiu, etc.) at the approved dose but have poor clinical response (defined as not achieving PASI 50 during treatment)；

• Receipt of any other marketed or investigational biologic agent within 3 months or 5 half-lives (whichever is longer) prior to randomization;

• Receipt of any other investigational drug in 1 month or 5 half-lives (whichever is longer) prior to randomization;

• Those who have undergone surgical surgery within 4 weeks prior to randomization, or who plan to undergo surgical procedures during the study;

• Those who have lost blood or donated more than 400 mL of blood within 4 weeks prior to randomization;

• Receipt of immunoglobulin or blood products within 4 weeks prior to randomization;

• Systemic treatment drugs or immunosuppressants for psoriasis within 4 weeks prior to randomization, including but not limited to retinoids, glucocorticoids, methotrexate, cyclosporine, azathioprine, Janus kinase (JAK) inhibitors, etc;

• Use of strong CYP450 inducers (such as rifampicin, phenobarbital, carbamazepine, phenytoin, etc.) within 4 weeks prior to randomization;

• Received topical or systemic phototherapy within 4 weeks prior to randomization, including but not limited to Narrow-band ultraviolet B (NB-UVB), photochemotherapy (PUVA), 308nm excimer light;

• Use of topical drugs that may affect the severity of skin lesions in psoriasis within 2 weeks prior to randomization, including but not limited to glucocorticoids, urea, >3% salicylic acid, α or β hydroxy acids, retinoids, vitamin D3 analogues, calcineurin inhibitors, Phosphodiesterase-4 (PDE-4) inhibitors, etc. (Note: Mild emollients (without active substances such as urea, salicylic acid, α, or β hydroxy acids) are allowed to be used at all sites, but should not be used within 24 hours prior to each study visit);

• Potential difficulty in blood collection, with a history of fainting needle and blood sickness;

• Allergy to any of the known ingredients of the TQH3906, or any previous history of severe drug allergies.

• Those with a history of substance abuse;

• Has any other reasonable medical, psychiatric, or social reason that, in the opinion of the investigator, precludes participation in this study.