responsible for short-term and probably long-term marrow recovery 
are believed to express the CD34 antigen. It has been demonstrated 
that the CE34+ subpopulation is capable of producing marrow 
recovery post-ABMT (24, 25, 15). We will study whether the neo - 
transduced CD34+ stem cells and their progeny can be found in 
recovering and steady state marrow post-ABMT and whether 
administering chemotherapy with and without G-CSF increases the 
number of these cells. 
We are interested in administering chemotherapy to patients with 
residual or relapsed disease post-ABMT to study whether a 
chemotherapy-induced nadir will increase the number of cycling 
stem cells and progenitors bearing the neo gene. Similarly, we will 
study whether the addition of G-CSF increases the number of neo- 
bearing BM or circulating cells in the post-nadir recovery period. In 
the future we plan to conduct ABMT/gene transfer studies infecting 
BM cells with the mdr 1 -transduced BM cells increases the number 
of circulating leukocytes bearing the mdr 1 gene (38). In this study 
we will offer relapsed patients treatment with vinblastine, with 
and without G-CSF, to determine whether the stem cell and 
progenitor cycling caused by the nadir increases the number of neo - 
transduced cells. This information will also serve as control data 
for our future mdr 1 transfer study. Vinblastine is reasonable 
salvage therapy for metastatic breast cancer. It is well-tolerated 
and is associated with a 20% response rate (50). Few metastatic 
breast cancer salvage regimens have higher response rates without 
also causing severe myelosuppression. 
Me .chanisni.Ql Breast. C anc er . . Relapse Fpll Qw in aJJiqh.D.Q5s 
Chemotherapy and ABMT 
Hematopoietic stem cell harvests from bone marrow peripheral 
blood may contact occult tumor cells. Histologically normal bone 
marrow aspirates or harvests of breast cancer patients have been 
found to contain occult metastatic tumor cells in up to 30% of 
patients in some series (26, 27, 28). The importance of occult bone 
Recombinant DNA Research, Volume 16 
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