In the present study, we document, for the first time, that WJ-MSC transplantation decreased the level of HbA1c; increased the level of fasting C-peptide; decreased the fasting glucose level, 2 h postprandial blood glucose level, insulin requirement and oral hypoglycemic drugs; and reduced the systemic inflammation and T lymphocyte counts in patients with T2DM.
HbA1c is a glycemic indicator and reflects the average blood glucose over the preceding 8 to 12 weeks
. We detected the maximum decrease in HbA1c in the first three months after WJ-MSC transplantation, and the maximum decrease in both the fasting glucose levels and 2 h postprandial glucose levels occurred at the same time, implying that WJ-MSC treatment can improve glycemic control in a short time. It is noteworthy that the levels of the fasting serum C-peptide and 2 h postprandial C-peptide decreased to different degrees in this period. Strangely, we also found that β cell function decreased, as assessed with the HOMA calculator, in 12 of 22 patients at one month. The intrapancreatic endovascular injection could cause impairment of the organ in case one or more of the following events were to occur: 1) puncturing a large artery causing a major bleed; 2) causing an instant blood-mediated inflammatory reaction (IBMIR) in the pancreatic circulation and 3) causing the formation of blood clots, all of which could ultimately lead to a pancreatic infarction, and erase precious beta cells. The use of a contrast agent during the intervention may facilitate the identification of potential injuries to the pancreas. Further investigations are needed to address the safety concerns of this delivery method. At this time-point, 17 patients who received insulin therapy had a reduction in their insulin requirement from 0.48 ± 0.21 IU/kg/day at baseline to 0.34 ± 0.20 IU/kg/day. The most probable reason for this contradictory phenomenon is that the infused WJ-MSCs rapidly improved general insulin resistance, which led to a reduction in endogenous insulin secretion and the need for exogenous insulin injection. At the subsequent three-month and six-month follow-ups, the levels of fasting C-peptide increased gradually and reached a peak value at six months, which suggests that WJ-MSC transplantation enhanced the basal insulin secretion. The results of β cell function, as assessed with the HOMA calculator, in 12 out of 22 patients also verified this conclusion. At this stage, the fasting glucose levels showed a downward trend but were not statistically significant. In addition, the 2 h postprandial glucose levels showed a significant decrease compared to the baseline and remained constant, suggesting a longer lasting effect of WJ-MSC treatment.
Because the HbA1c and C-peptide of patients who received WJ-MSC treatment showed the best control at the sixth month, we chose the sixth month to examine the therapeutic mechanism of WJ-MSC in 22 enrolled patients. Mounting evidence has demonstrated that chronic and low-grade inflammation plays an important role in the development and progression of T2DM
. Inflammation can not only impair insulin signaling and contribute to insulin resistance
[19, 20] but can also trigger β cell apoptosis and reduce insulin secretion
. Many pro-inflammatory cytokines, such as TNF-α, IL-6 and IL-1β, have been demonstrated to be elevated in T2DM patients and participate in the development of insulin resistance
[21, 22]. Numerous studies have verified that MSCs show promising therapeutic potential in autoimmune disease
 and neurological abnormalities
 through the modulation of the inflammatory condition. Our studies also demonstrated that the levels of pro-inflammatory cytokines, including IL-6 and IL-1β, were significantly decreased six months after WJ-MSC transplantation. CM Larsen and colleagues found that an IL-1 receptor antagonist improved glycemia and beta-cell secretory function accompanied with a reduction in markers of systemic inflammation, including C-reactive protein and IL-6. Through correlation analysis, the serum pro-inflammatory cytokines were not significantly correlated with the improvement in HbA1c
. Our data also did not show a correlation among the levels of HbA1c and IL-1β and IL-6, but we found a significant correlation between the changes in the levels of fasting C-peptide and IL-6, suggesting that reduced systemic inflammation may play an important role in improving basal insulin secretion. We believe that WJ-MSCs may exert their therapeutic potential partly by regulating systemic inflammation.
Shawn Winer et al. found that CD4+ T lymphocytes residing in visceral adipose tissue controlled insulin resistance in mice with diet-induced obesity, and a similar process occurred in humans. The treatment of obese wild type (WT) and ob/ob (leptin-deficient) mice with a CD3-specific antibody or its F(ab’)2 fragment reduced the predominance of Th1 cells compared to Foxp3+ cells and reversed insulin resistance for months
. Ulrich Kintscher et al. showed that pro-inflammatory T-lymphocytes played an important role in the initiation and perpetuation of adipose tissue inflammation and the development of insulin resistance (IR)
. Our data showed that the numbers of CD3+ and CD4+ T lymphocytes were reduced in 12 of 14 patients three months after WJ-MSC treatment, and there was a significant correlation between the changes in the levels of fasting C-peptide and the numbers of CD3+ T lymphocytes, suggesting that WJ-MSC transplantation may participate in the regulation of the immune process and reduce inflammation and insulin resistance, improving diabetic symptoms. Future studies are needed to determine the correlation between the T lymphocyte counts and diabetic symptoms in more cases.
For MSC delivery, some studies have chosen intravenous delivery
 or endovascular catheterization
, and a few studies have used both approaches. We believe that the majority of intravenously transplanted MSCs will be trafficked to the lung and the other peripheral tissues
; thus, the number of MSCs recruited to islets is limited. Local intra-arterial (IA) injections can enhance the accumulation and increase the number of MSCs in islets. Nevertheless, safety concerns related to this delivery method will have to be addressed in future studies. T2DM is a metabolic disease characterized by insulin resistance and beta-cell dysfunction. Therefore, we believe that all of the delivery approaches have limitations, and we chose a combination of two approaches in our study. MSCs injected through intravenous delivery improve the symptoms of peripheral tissues, and IA injected MSCs may exert functions in islets. Based on our study results, we speculate that intravenously infused MSCs can inhibit systemic inflammation and improve insulin resistance, whereas local intra-arterial injection infused MSCs can improve islet inflammation and reduce the damage to β cells.
Many studies have reported a therapeutic effect of umbilical cord-derived MSCs in a variety of diseases and no obvious adverse effects were reported
[11, 29, 30]. XY XY and colleagues designed a clinical study to treat foot disease in patients with type 2 diabetes mellitus using hUCB-MSCs and there is no related adverse effect reported
. J Hu et al. assessed the long-term effects of the implantation of WJ-MSCs for new-onset T1DM. There were no obviously adverse reactions in any of the patients who completed the study protocol, and no chronic side effects or lingering effects appeared during the follow-up
. Lingyun Sun’ study explored the therapeutic effect of UC-MSCs in severe and treatment-refractory systemic lupus erythematosus (SLE). No treatment-related adverse events occurred during or after UC-MSC transplantation, and UC-MSC transplantation was well tolerated by all patients
. We also have the same results on the safety of WJ-MSC transplantation with all the above trials.