The purpose of this study is to investigate the safety and efficacy of umbilical cord derived mesenchymal stem cells (UC-MSCs) in patients with moderate to severe psoriasis vulgaris. Any adverse events related to UC-MSCs infusion will be monitored and the patients will be assessed by Psoriasis Activity and Severity Index (PASI) and Dermatology Life Quality Index (DLQI) in the baseline and after MSCs infusions.

Psoriasis is considered as an incurable immune-mediated inflammatory skin disease. The widely used treatments include topical agents, systemic medications and biologic agents, but all of them have some drawbacks or limitations. Besides, non-standardized treatment or the disease itself may lead transformation to other diseases, which add more importance to finding improved management strategies.

Mesenchymal stem cells (MSCs) are a heterogeneous population of cells that can differentiate into bone, cartilage and fat cells. They have several functions, such as migration to skin lesions, immunomodulation, limitation of autoimmunity and local paracrine effects. It reported MSCs have already been used in some kinds of autoimmune disease, such as systemic lupus erythematosus (SLE), systemic sclerosis, crohn disease, rheumatoid arthritis et al.

In this study, consenting umbilical cords are donated by healthy donors. After several processing steps, UC-MSCs are separated and froze for future infusions. When volunteers are recruited, their condition will be assessed by Psoriasis Activity and Severity Index (PASI) and Dermatology Life Quality Index (DLQI). Then MSCs will be infused according to a standard scheme. After all 6 infusions, the patient will be re-assessed by the PASI and DLQI and will be followed up for one year.

Inclusion Criteria:

• Diagnosis of stable psoriasis vulgaris for at least 6 months
• Baseline Psoriasis Area and Severity Index (PASI) score >= 8
• Despite systemic or topical treatment, psoriasis is still in active or recurrent condition
• No other psoriasis management (topical or systemic) during the UC-MSCs infusions
• Willing and able to comply with all study requirements and provide informed consent

Exclusion Criteria:

• Other types of psoriasis, such as pustular psoriasis, psoriatic arthritis
• With other disease
• Systemic treatments within 4 weeks before the baseline visit
• Topical treatment within 2 weeks before the baseline visit
• Uncontrolled active infections
• Evidence of infection with Hepatitis B Virus (HBV), Hepatitis C Virus (HCV), or Human Immunodeficiency Virus (HIV)
• History of severe systemic disease or malignancy
• Pregnant or lactating females, or willing to have a baby in the next year
• Cannot be traced on time
• Any other situations not suitable for this study determined by the investigators