This study will explore safety and efficacy of allogeneic mesenchymal stem cells transplantation (MSCT) to treat patients with diagnosis of primary Sjögren's Syndrome (pSS) who have been resistant to multiple standard treatments. The underlying hypothesis is that the pSS condition is caused by an abnormal immune homeostasis that can be restored by MSCT.

• To test a new approach using allogeneic derived mesenchymal stem cell based therapy (MSCT) to treat refractory primary Sjögren's Syndrome (pSS)
• To determine the disease-free survival in pSS patients treated with MSCT in terms of disease activity index, pSS serology and salivary gland function
• To assess adverse events of allogeneic MSC transplantation
• To assess the association of disease activity index, pSS serology levels, and saliva flow rate at baseline with disease-free survival

Inclusion Criteria:

• All patients fulfilled the international classification criteria (2002) for primary Sjögren's Syndrome, man or woman aged from 15 to 70 years old, Sjögren's Syndrome Disease Activity Index (SSDAI)≥8.
• Stimulated whole saliva flow rate less than 1~6ml/6min.
• Patients must be informed of the investigational nature of this study and give written informed consent in accordance with the institutional and hospital guidelines.
• Women of reproductive potential may not participate unless they have agreed to use an effective contraceptive method while on this trial and for 12 months following treatment. Women of child-bearing potential must have a pregnancy test performed within 72 hours prior to initiation of treatment.

Exclusion Criteria:

• End-stage renal failure.
• Severe cardiopulmonary compromise, or other system failure.
• Active, uncontrolled infections.
• Pregnant or nursing women may not participate due to the possibility of fetal harm or harm to nursing infants from this treatment regimen.