8.2 Transduction of Malignant Progenitor Cells 
The transduction efficiency for acute myeloid leukemia clonogcnic cells has 
been reported as between 5 and 50% (Benchimole et al 1989). Our data (see 
Data appendix) eorroborate these results. At present, there is no way of 
assessing whether "clonogenic cells" and AML "stem cells" are identical or 
have the same transduction efficiency in man. But if we assume that, 
transduction efficiency for clonogenic cells and stem cells is identical, and take ’ 
a figure of 10% as average efficiency, then only 3% of the total malignant 
"stem cells" present in a harvested marrow will be transduced in the 30% 
aliquot exposed to the veetor. This makes it unlikely that relapse from a 
SINGLE progenitor would be detected unless >50 patients were studied - a 
number not currently feasible. 
Polyclonal relapse with or without involvement of multiple lineages 
(Possibilities 2 or 3 in section 7.2 above) would be more readily detected with 
a probability that would increase as the number of AML "stem cells" 
increased. The marrow relapse rate in patients reeeiving ABMT for AML is 
ea 50% at 3 years. At least one marked relapse would therefore be detectable 
in a cohort of 12 individuals with a probability of >90% even if only 10 cells 
contribute to the relapse. In any one individual who relapses, there is a 60% 
chance of detecting a marked relapse if 30 cells contribute, and >95% chance 
if 100 eells contribute. 
The minimal number of patients we plan to study with transduction is 
therefore 10-15 over three years. 
8.3 Transduction of Normal Progenitors 
Because the probability of transducing a human stem cell in patient 
recovering from chemotherapy is unknown (see Data Appendix) and because 
the number of pluripotent stem cells contributed by an autologous marrow 
graft is also unknown, it is not possible to assess the number of patients 
required to undertake this subsidiary aim. But if transduction into early 
progenitors is possible, then data on the value of this approach for 
investigating stimuli which modify stem cell behavior could readily be obtained 
within the first 12 patients, sinee even a single positive patient would be 
informative. Similarly, since marking of long lived committed progenitors is at 
the 10-20% level, information on stimuli affecting the growth of these cells 
should also be obtained within the first 12 patients. Should the first 12 patients 
show no evidence of progenitor marking, this component of the study would 
not be continued separately from the primary aim of analyzing the source of 
relapse. 
Recombinant DNA Research, Volume 14 
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