(Eglitis et al.. 1985). murine hematopoietic cells were infected in either the 
presence or absence of IL-3 but without preselection or pretreatment. There 
was only a small increase in the infection rate in the presence of IL-3. and 
the Neo R gene was expressed in variable amounts in several individual spleen 
foci as assayed by direct analysis of the level of NPT enzyme activity. In 
addition. In tissue extracts from reconstituted animals. NPT activity was 
detected in the bone marrow of 3 out of 4 mice and in peripheral blood cells of 
one of the bone marrow positive animals four months after the time of 
transpl ant. 
Results of our work with the SAX vector containing human ADA for gene trans- 
fer In monkey bone marrow i£ vivo are presented In the Overview section above. 
c. Laboratory studies pertaining to the safety of the 
del Ivery/expression syste m 
(1) If a retroviral system Is used: 
(a) What cell types have been Infected with the retroviral 
vector preparation? Which cells. If any. produce 
Infectious particles? 
A number of murine and large animal cell lines as well as primary hemato- 
poietic cells have been infected with the SAX construct packaged in a wide-host 
range (amphotropic) viral particle (from S3A producer cells); these studies are 
described in Section I.B.2.a. Currently all supernatants from our S3A producer 
cells contain a low level of murine replication-competent virus in the range of 
0.5-50 x 10 4 focus-forming-units (ffu) per ml based on an S + L~ assay using 
feline cells. These same preparations have vector viral particles at a titer of 
0.5-50 x 10 6 Neo R colony-forming-units (cfu) per ml. Thus some preparations 
actually have a replication-competent titer that is 10% of the vector titer. 
Recombinant DNA Research, Volume 12 
[ 45 ] 
