Autologous Bone Marrow Transplantation - Blog Science Connections

Leukemia Cell Sensitioity to Immunotoxins 367
RESULTS
In the presence of NH 4
CI (10 mM), Fab Tl 01 -RTA showed three distinct
ranges of cell killing efficacy on CEM III cells as evaluated by DEA (Table 1).
First, the high cell killing efficacy for immunotoxin concentrations ranging
from 10 8
to 10~ 1 °M left from 5.1% to 19.7% residual viable cells. For these
concentrations, the cloning assay showed a cytoreduction of 6 logs. Second,
the medium-range cell killing efficacy for a concentration of 10 1 1 M left from
63% to 77% residual cells. For this concentration, the cloning assay showed a
cytoreduction of 2.8 logs. Third, poor or no cell killing efficacy existed for
immunotoxin concentrations of 10 -12
M, which left percentages 90.3% and
higher. No significant cytoreduction was observed by the cloning assay at
these concentrations.
In the absence of NH 4
CI, Fab T101-RTA could induce at 10 8 a cytoreduction
of 2.9 logs. At this concentration, DEA could detect 44-57%
(mean, 48%) residual viable CEM III cells. Examined together, these results
showed that DEA could identify three distinct levels of sensitivity to Fab
Tl 01 -RTA: 1) a high level of sensitivity with percentages lower than 16%, 2) an
intermediate range of sensitivity with percentages varying from 40% to 80%,
and 3) a low level of sensitivity with percentages higher than 90%.
Malignant T cells displayed very distinct sensitivities to Fab T101-RTA,
depending on the presence or absence of NH 4
C1. In the presence of NH 4
C1
(10 mM) T cells of both chronic lymphocytic leukemia (CLL) and acute
lymphocytic leukemia (ALL) showed extremely high susceptibility to Fab
Tl 01 -RTA equal to or greater than that observed for CEM III cells (see Table
2). Without NH 4
C1, malignant T cells displayed a wide range of susceptibility
Table 1. Dose Effect of Fab T101 -RTA on CEM III Cells With and Without NH 4 CI
as Assessed by Cloning Assay and DEA
Concentration of Fab T101-RTA (M of A-chain)
Measure 10-8 10-9 10-10 10" 10 1 2
Log kill with
NH 4 CI (cloning
assay)
6.0 6.0 6.0 2.8 0.5
R" with NH4CI
(DEA) (%)
5.1-13.8
(m =10.2)
5.0-16.3
(m = 10.8)
11.7-19.7
(m = 14.5)
62.9-76.8 90.3-104.5
(m = 69.4) (m = 98.1)
Log kill without
NH 4 CI (cloning
assay)
2.9 1.8 0.5 0 0
R a
without NH 4 CI
(DEA) (%)
44.1-57
(m = 48)
81.9-97.4
(m = 88.1)
92.0-116.6
(m = 103.4)
NT
NT
Abbreviations: DEA, dye exclusion assay; NT, not tested.
a
R = percentage of residual viable CEM III cells 48 hours after treatment.