The aim is to Investigate the safety and efficacy of Portal vein infusion Allogeneic Human umbilical cord mesenchymal stem cells combined with Allogeneic islet transplantation for the treatment of diabetes

This is an investigator-initiated trial (IIT). The first part is an open-label, dose-escalation study involving 9 patients between the ages of 18 and 70. The second part is a non-randomized, active comparator-controlled IIT with a parallel design, comparing allogeneic islet transplantation combined with human umbilical cord mesenchymal stem cells (hUCMSCs) to allogeneic islet transplantation alone in patients with diabetes.Besides safety, preservation of endogenous insulin production (measured as C-peptide concentrations) together with metabolic control, diabetes treatment satisfaction and immunological profile will be assessed.

Inclusion Criteria:

1. Meets the 1999 World Health Organization diagnostic criteria for diabetes.

2. Aged 18-70, no gender restriction.

3. Islet function failure: fasting C-peptide < 0.1 nmol/L, 2-hour postprandial C-peptide < 0.2 nmol/L, and HbA1c ≥ 7%.

4. Meets the indications for islet transplantation alone:

   i. Type 1 diabetes patients who experience unstable blood glucose despite strict insulin therapy, including frequent hypoglycemia or at least one severe hypoglycemic event in the past 12 months, or those with serious complications in other organs such as the kidneys; ii. Type 2 diabetes progressing to islet failure with poor blood glucose control as described above; iii. Patients with chronic pancreatitis or non-malignant pancreatic tumors who have undergone total or near-total pancreatectomy may receive autologous islet transplantation concurrently or allogeneic islet transplantation later.

5. The patient and their family or legal guardian voluntarily consent to stem cell transplantation therapy and sign the informed consent form.

Exclusion Criteria:

1. Diabetic ketoacidosis that is not yet controlled.
2. Severe allergic constitution, meaning prone to allergic reactions without a clear and identifiable cause.
3. BMI < 14 or > 35.
4. Severe anemia (hemoglobin < 8 g/dL in males, < 7 g/dL in females).
5. HIV-positive, carriers of viral hepatitis or in the active phase, or other uncontrolled infectious diseases.
6. History of acute pancreatitis, pulmonary embolism, or other thrombotic diseases, as well as severe heart, liver, kidney, respiratory, or neurological diseases.
7. Patients with gestational diabetes, monogenic diabetes, diabetes due to pancreatic damage, or other secondary diabetes (e.g., diabetes caused by Cushing's syndrome, thyroid dysfunction, or acromegaly).
8. Pregnant women or those planning pregnancy within 3 months before or after treatment, and women who are breastfeeding.
9. Patients with mental illness, alcohol or drug abuse, who are unable to cooperate with treatment.
10. Known or suspected tumors.
11. History of other autoimmune diseases or hematological disorders.
12. Any other clinical conditions that, in the investigator's judgment, may pose a risk to the participant's safety.