INS and type 2 diabetes mellitus: On the contrary, UCB was found to be uniformly ineffective; HbA1c% (pooled-estimate − 0.091, 95%CI (− 0.454, 0.271); p = 0.622), significantly deteriorated C-peptide levels (pooled-estimate − 0.789; 95%CI (− 1.252, − 0.325); p < 0.001) and daily insulin-requirement (pooled-estimate 0.916; 95%CI (0.247, 1.585); p = 0.007). All these observations remained consistent when we carried out sub-group meta-analysis for T1DM and T2DM and also when we compared patients who received WJ-MSCs or UCB to controls.