MKI67 and glioblastoma: However, when co-cultures were established, a significant reduction of Ki-67 antigen expression occurred in GBM CSCs (from 92% to 63% in CSC1 and from 90% to 67% in CSC2; Figure 5B), demonstrating that in the presence of UC-MSCs both CSC cultures reduced the proliferation rate, in line with the FACS results described in Figure 4.