Autologous Bone Marrow Transplantation - Blog Science Connections

372 Panel Discussion: Session IID
DR. C. READING: I just want to ask you if you used immunotoxins and
then froze the marrow and thawed it again, would the bystander effects be
much worse? Have you investigated that?
DR. BAST: We have not. Before this goes to clinical trial, which we
anticipate doing in the not too distant future, that is one of the essential
controls. We are aware of that problem, but we have not investigated it. We
have been looking for the optimal dose of immunotoxin which we have only
recently discovered.
DR. G. SPITZER: Bob, I wanted to ask you if you noticed any patient
variability in the sensitivity to chemoimmunopurging.
DR. BAST: Within the limits of the data of the six patients that 1 showed
you, we did not see dramatic differences in that we could eliminate all of the
colonies that we could measure with the combination. However, this is a
suboptimal system. A subset of these, two leukemic patients, are responsive
to IL-2 or conditioned medium, and we will probably be able to improve that
system by a log in the near future. 1 think that we may be able to find more
subtle differences in the susceptibility of different patient cells. In our
experience to date, virtually every leukemia and lymphoma that we have
measured at Duke University has been 3A1 positive in contrast to the data
with some of the cell lines that I presented. So there is some hope that this will
be a relatively universal reagent, although there may be occasional patients in
which a second immunotoxin might be useful because of the heterogeneity
issue rather than the saturation.
DR. M. FAVROT: 1 would like to ask you two more questions. When you
are working with fresh tumor samples, do you use the limiting dilution assay
to detect residual tumor cells? What is your limit of detection compared with
immunofluorescence?
DR. BAST: 1 suspect, Marie (Dr. Favrot), that you could be much more
sensitive with a morphologic technique or with an immunofluorescence
technique. Whether it is more relevant, I think, is the difficult issue. Meedless
to say, I think that from your work, as from ours, we are interested in getting rid
of the clonogenic cells; however, cases in which we are growing only 20 or 50
colonies per 10 5
cells, the sensitivity of that technique is so low that I am sure
that tumor cell detection can be done better with immunofluorescence.