marrow stored for transplantation at a much later 
date. Criteria for marrow harvest must include: 
5.11) 
Patients must be greater than one month 
from cytotoxic drug therapy at the time 
of marrow harvest. 
5.12) 
Pre-harvest bone marrow aspirate and 
biopsy performed within 1 weeks of 
harvest must demonstrate adequate 
cellularity (based on bone marrow biopsy 
cellularity of greater than 40%, taking 
into account sampling error) , and no 
evidence of leukemia (<5% blasts and 
absence of leukemic markers, such as Auer 
rods) . 
5.13) 
Cytogenetic analysis performed on the 
pre-harvest bone marrow must show no 
evidence of malignancy. 
5.14) 
Cell harvest must be sufficient for 
marrow reconstitution (cell yield must be 
greater than 2.0 x 10® nucleated 
cells/kg) . This should yield sufficient 
cells for bone marrow transplantation 
even if the cells taken for vector 
preparation cannot be used. 
5.15) 
No more than 30% of the harvested marrow 
will be exposed to the retroviral vector. 
5.2) Vector Preparation 
5.21) 
The LNL-6 vector 
The LNL-6 vector (Figure 1) was developed 
in the laboratory of A. Dusty Miller (53) 
and is a safety-modified version of the 
retroviral vector N2 . The vector was 
constructed by modifying the Moloney 
murine leukemia virus (MoMLV) by removing 
the viral genes and replacing them with 
the bacterial neo R gene. The vector has 
a number of modifications to decrease the 
likelihood of successful recombination 
between the vector and packaging cell 
genome that might result in replication- 
competent virus. The modifications 
include deletion of 5' and 3' sequences 
to minimize homology and substitution of 
[476] 
Recombinant DNA Research, Volume 15 
