Review 
This section will address studies of retroviral vector gene transfer 
in mammalian systems in vitro and in vivo . These studies have established the 
feasibility of using retroviral vectors to transfer functional genes. 
The efficiency of infection and expression depends on both the vector construct 
and the particular target cell. 
Temin has recently reviewed retroviral vector design as well as early 
studies utilizing a number of inserted genes (Temin. 1986). Common to all 
these vectors is the use of the viral long terminal repeat (LTR) to provide 
transcriptional controls and integrative functions regardless of the species of 
virus from which the vector is derived. A further development in vector design 
has been the elimination of LTR enhancer and promoter sequences, the so-called 
deleted LTR CdLTR) . in order to reduce (a) the likelihood of insertional 
oncogenesis (Yu et al.. 1986) and (b) the possibility of interference between 
the LTR and internal promoters (Emerman and Temin. 1984). These vectors, 
called SIN (self-inactivating) vectors by Gilboa, unfortunately suffer from 
titers that are too low to be useful clinically at this time (Yu et al.. 1986). 
Another development which has promoted the clinical usefulness of retroviral 
vectors has been the introduction of helper-free packaging lines. These are 
discussed in section I.B.l .b. (2) . The genes in vectors which have been 
successfully used to transduce cells are summarized in Appendix A. Table 1. 
For the purposes of this review, we will focus on studies of our own 
collaborative group and others concerning the transfer of functioning 
retroviral vectors into hematopoietic cells, whether primary cells or 
established cell lines, in vitro and in vivo , and in a number of different 
species including mouse, monkey, dog, sheep, and man (in vitro only) . 
[ 22 ] 
Recombinant DNA Research, Volume 12 
