1.5 
1 . 6 
analogous to our proposal in this protocol and 
underscores the feasibility of this approach. 
Clinical 
Experience with retroviral mediated gene transfer into 
human marrow cells 
Studies of retroviral gene transfer in relapsed 
patients undergoing autologous bone marrow 
transplantation (ABMT) for acute leukemia have provided 
evidence for successful marking of human hematopoietic 
progenitor cells (15 and M. Brenner, unpublished data). 
Patients have now been followed for up to one year 
after ABMT: analysis of these patients has documented 
gene transfer into all lineages of marrow- derived cells 
including neutrophils and lymphocytes. These studies 
employed vectors very similar to those to be used in 
this study and suggest that retroviral mediated gene 
transfer into very primitive hematopoietic progenitor 
cells is possible. Furthermore, since the marrow was 
not cultured in the presence of hematopoietic growth 
factors during the transduction procedure, the 
efficiency of gene transfer in these studies would be 
expected to be lower than might be achieved using 
methods proposed in this protocol. 
Ability to transfer marrow progenitor cells into non- 
ablated recipients 
In mouse models, investigators have demonstrated 
successful transplantation of marrow stem cells into 
recipient mice without first "making space" in the 
marrow environment with ablative treatments (16-19) . 
Long-term chimeras up to two years post transplantation 
could be established without myeloablation. These 
experiments suggest that engraftment of autologous 
cells treated ex vivo with retroviral vectors may be 
possible without previous myeloablation. Further 
experience with transplantation for human 
immunodeficiency disorders such as severe combined 
immune deficiency (SCID) and Wiskott-Aldrich syndrome 
has supported the concept that prior myeloablation may 
not be necessary for engraftment of marrow cells. 
Rationale 
As outlined in the previous sections, we have 
demonstrated that our retroviral vector can transfer 
and express the FACC gene in the target population 
CD34- enriched progenitors of FA(C) patients. The level 
of expression was sufficient to "rescue" stem cells in 
our functional assay in a manner which should be 
directly analogous to our proposed protocol. Human and 
animal experience suggests that it should be possible 
to engraft hematopoietic stem cells without requiring 
ablation. Gene corrected stem cells would be expected 
to have a survival advantage within the hypoplastic FA 
marrow environment. All components necessary to 
execute the plan in this protocol have been 
demonstrated. 
Obi ectives 
1.61 Primary Objectives: 
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Recombinant DNA Research, Volume 19 
