We have also utilized cell -mediated gene transfer to deliver 
genes to specific sites in vivo . Vascular smooth muscle cells or 
| endothelial cells, transduced in vitro with E. coli p- 
galactosidase have provided a vehicle to deliver this and other 
recombinant genes into localized arterial segments (5,6). We 
infected either endothelial or vascular smooth muscle cell lines, 
established from Yucatan minipigs, with the BAG retroviral vector 
(7) and selected populations of transduced cells which have been 
introduced in vivo . 
These studies demonstrate that recombinant genes can be 
expressed in vivo by several strategies. Cell-mediated gene 
transfer can be achieved using vascular cells (5,6). This method 
is now being used to study the effects of expressing recombinant 
genes for cytoplasmic, membrane bound, or secreted protein 
products within living animals. Second, direct introduction of 
recombinant genes in vivo has been achieved (1) and provides a 
way to modify cells at specific sites in vivo . 
1.4 Immunotherapy of malignancy. 
The immune system not only provides protection against a 
variety of pathogens, but also appears to contribute to the 
surveillance and destruction of neoplastic cells. Several 
cellular and humoral immune effectors inhibit tumor cell growth. 
Cellular mediators with anti-tumor activity include MHC- 
restricted cytotoxic T cells, reviewed in (8) , natural killer 
(NK) cells (9,10) and lymphokine-activated killer (LAK) cells 
(11) . Cytolytic T cells which infiltrate tumors have been 
isolated and characterized (12) . These tumor infiltrating 
Recombinant DNA Research, Volume 15 
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