Autologous Bone Marrow Transplantation - Blog Science Connections

Leukemia Cell Sensitivity to Immunotoxins 369
Table 3. Sensitivity of Fresh B-CLL Cells to Fab T101-RTA With and Without
NH4CI as Assessed by FDA-PI Dye Exclusion Test
R with
R with
Fab T101-RTA Fab T101-RTA Mean Density
Patient Without NH 4CI With NH 4CI (10-2 M) of T65 Antigen
1 36.7 27.9 2,500
2 43.5 15.0 35,000
3 46.0 34.6 20,000
4 53.9 37.0 10,000
5 78.0 39.6 5,500
6 93.2 74.8 10,000
7 100.0 86.2 6,000
CEM III . 48.1 ± 6
(log kill = 2.9)
10.2 ± 5.7
(log kill = 6)
30,000
Abbreviations: B-CLL, B-cell chronic lymphocytic leukemia; FDA-PI, fluorescein
diacetate-propidium
iodide.
3
Ft = percentage of residual living cells 48 hours after treatment (24-hour
incubation) with immunotoxin (70 -8 M).
sensitivity to Fab Tl 01 -RTA (equal or higher than CEM cells) and B-CLL cells
displayed a lower sensitivity. Furthermore, without NH 4
C1, high or medium
range cytoreduction (higher than or equal to 3 logs) could be expected in
most T-cell malignancies, suggesting the high potential of Fab T101 -RTA for
in vivo use, even if fully resistant Tl 01-positive malignant cells were found.
No correlation could be established between mean density of T65 antigen
and Fab T101-RTA cell-killing efficacy within a range of 2500-123,000
molecules/cell. Those findings are not in line with those recently reported
from studies on continuous cell lines in which the influence of mean density
of target antigen on immunotoxin cell-killing efficacy was clearly demonstrated
(3). These conflicting results may demonstrate that other factors can
influence individual susceptibility of target cells to relevant immunotoxins.
Finally, despite its relatively low sensitivity compared with the cloning
assay, DEA allowed the detection of distinct susceptibilities of fresh malignant
blood cells to Fab Tl 01 -RTA. However, especially in malignant T cells, Fab
Tl 01 -RTA could induce in most cases a significant cell-killing efficacy greatly
improved by the use of NH 4
C1 as an enhancing agent.
ACKNOWLEDGMENT
We thank Dr. F. Huguet for providing leukemia cells, and we are also
grateful to C. Clausner for secretarial assistance.