MSCs from ALL patients (ALL-MSCs) protect l-asparaginase-treated leukemia blasts better than MSCs from healthy donors (HD-MSCs). (A) MSCs from an ALL patient (UPN #14, supplemental Table 2A) or from a healthy donor (UPN #11, supplemental Table 2B) were cocultured for 48 hours with RS4;11 ALL cells in the presence of l-asparaginase (ASNase, 1 U/ml) or l-asparaginase + methionine-l-sulfoximine (ASNase + MSO, 1 mM). The percentages of dead RS4;11 cells, obtained in a representative experiment, are shown. (B) The protection index was calculated on RS4;11 cells treated for 48 hours with ASNase or ASNase + MSO in the presence of ALL- or HD-MSCs derived from 3 distinct patients (UPN#14-15-16, supplemental Table 2A) or healthy donors (UPN#11-14-16, supplemental Table 2B). (C) The protection index was calculated on primary blasts treated for 48 hours with ASNase or ASNase + MSO in the presence of unrelated ALL- or HD-MSCs. For panels B and C, means ± SD of 3 (B) or 5 (C) independent experiments performed with MSCs from 3 (B) or 2 (C) different patients (UPN#11-12, supplemental Table 2A) or healthy donors (UPN#1-3, supplemental Table 2B) were used. For panel C, blasts from 3 different, unrelated ALL patients (UPN#4-5-6, supplemental Table 2A) were used. UPN#4-5 have been cocultured with UPN#11-12 (supplemental Table 2A) and UPN#1-3 (supplemental Table 2B), and UPN#6 has been cocultured with UPN#11 (supplemental Table 2A) and UPN#1 (supplemental Table 2B). For the calculation of the protection index, see Materials and Methods. *P < .05 (one-tailed Student t test for paired samples). For panels B and C, in each panel different symbol identifies MSCs from an individual donor.