ablative dose of cyclophosphamide chemotherapy (4 gms/m^) , collection 
of CD34 selected peripheral blood cells early in the course of 
hematopoietic recovery (the precise time of which may vary for each 
patient but is usually as soon after a total white cell count of 
2,000/cu mm has been reached) , has produced transduction frequencies of 
the very early precursor cells, the long-term marrow culture initiating 
cells (LTCIC) in the range of between 5-20% in our own work and in that 
of others. The peripheral blood cells will be CD34 selected, and then 
incubated in vitro in the retroviral supernatant to introduce the viral 
MDR-1 into the patient's hematopoietic stem cells. We will then treat 
the systemic disease a single time before transplant, with a regimen 
which consists of high dose cyclophosphamide (1.5 g/m^/d x 3) thiotepa 
(200 mg/m^/d x 3) , and BCNU (150 mg/m^ qd X 3) . This regimen was chosen 
as it has agents which are active in breast cancer, and at the same 
time will provide suppression of the endogenous hematopoiesis needed to 
facilitate engraftment of the genetically-modified cells. We have 
significant institutional experience with this protocol. Following 
this single course of intensive systemic therapy, these patients will 
be transplanted with the genetically modified stem cells. Following 
recovery of hematopoietic function, the patients will receive cyclical 
Taxol therapy with starting dose at 60 mg/m^. The dose will be 
increased by a dose adjustment schema described in Section 5.4 from 60, 
120, 180, 225, and 275 mg/m^. This will enable us to increase the dose 
as the percentage of transduced cells increases without imposing 
toxicity on individual patients. The courses will be delivered every 
three to four weeks to a total of 12 courses, depending on recovering 
the ANC to 2000/mm^ and the platelet amount to 100,000/mm^. We will 
measure the levels of the cells which are modified by the MDR-1 
viruses, and monitor the rate of hematopoietic recovery, which should 
become more rapid with each cycle and should contain higher and higher 
percentages of MDR-1 cDNA positive cells due to the selective effect of 
the chemotherapy. Finally, once this principle of in vivo selection is 
established, it will be possible to increase the doses of Taxol with 
each cycle of therapy. The goal of this program is to establish this 
principle of in vivo selection of genetically modified cells, and to 
study their effect on the ability to deliver very intensive doses of 
combination chemotherapy, or at least in the initial phases, relatively 
intensive doses of Taxol following recovery of hematopoietic function 
after autologous stem cell marrow transplantation. This may have a 
beneficial effect on the survival of these patients in whom the 
inability to eradicate residual disease lead to an 80% expectation of 
dying of their disease within two years. 
3.0 DRUG BACKGROUND INFORMATION (See Appendix H) 
4.0 PATIENT ELIGIBILITY 
4.1 Advanced disease Stage III/IV breast patients who have not 
previously been exposed to Taxol and who have failed conventional 
dose therapy or induction therapy, who therefore have an 80% 
chance of dying of progressive cancer. Patients must be however 
at least partially sensitive to conventional dose chemotherapy. 
Patients must have measurable or evaluable disease and have not 
had irradiation to greater than 20% of marrow bearing areas. 
Recombinant DNA Research, Volume 19 
[527] 
