3.3.2 Murine Tumor Model Data 
3.3.2. 1 MURINE y-IFN VECTOR EXPRESSION AND MHC. The retroviral vector containing 
the murine y-IFN gene was generated and introduced into several murine tumor cell lines; L33 
(fibrosarcoma), B16F10 (melanoma), CT26 (colo-rectal carcinoma), and Lewis lung carcinoma. 
All transduced lines produced measurable levels of biologically active y-IFN detectable in the 
growth media compared with the non- transduced parent tumor cell lines (Table V). Unmodified 
CT26, however, displayed a low, but detectable, basal level expression of y-IFN (Table V). The 
effect of endogenous y-IFN expression on MHC Class I protein in L33, B16F10 and CT26 was 
determined by protein immunoblotting. With the exception of CT26, a large increase (>20-fold) in 
the level of MHC was observed in all y-IFN-vector-transduced tumor cell lines (Fig 6). CT26 
displayed relatively high basal levels of MHC, possibly due to the basal level of y-IFN produced 
by this cell line (Table V). Consequently, CT26 displayed only a modest (2-3-fold) increase in 
MHC expression (Fig 6A). FACS analysis indicates that the Class I MHC was cell surface 
associated (Fig 7). 
Transduction by murine y-IFN vector thus substantially increases the level of Class I MHC. 
Similar reports have been reported by other investigators (30). Since these proteins present antigen 
to the immune system, the effect of vector transduction should be to improve immune responses, 
especially those that are Class I restricted such as CTL. 
3. 3. 2. 2. TUMORIGENICITY OF MURINE y-IFN-EXPRESSING CELLS. Improved immune 
responses against y-IFN-transduced tumor cells might be reflected in a decrease in the tumorigenic 
properties of the tumor. The effect of endogenous y-IFN expression on the tumorigenic properties 
of the vector modified tumor cells was therefore assessed in syngeneic animals. Vector-modified 
L33 (Fig 8 A), B16F10 (Fig 8B), CT26 (Fig 8C), and Lewis lung (Fig 8D) were all substantially 
less tumorigenic than the corresponding unmodified parent tumor cell lines (Fig 8). 
In additional experiments, recombinant y-IFN protein added to the L33 of B16F10 cells did not 
affect tumorigenicity (Fig 8), even though control experiments indicate that treatment resulted in 
high level MHC expression for as long as 3 days after treatment (data not shown). This indicates 
that the effect of constitutive expression of y-IFN obtained by gene transfer can be superior to the 
effect obtained by treatment with recombinant y-IFN protein. Control experiments with vectors 
which express only Neo r did not affect tumorigenicity (data not shown), indicating that the effect is 
due to y-IFN expression per se and not due to the vector transduction process in general. 
[628] 
Recombinant DNA Research, Volume 17 
