melanoma. CTL plus IL-2 had marked therapeutic activity in the 3 and 7 day 
models, rendering most mice tumor-free. Some "cures' were still evident even 
in the advanced 10-day model. Anti-tumor effects of the CTL were dose-related 
and specific. IL-2 alone was ineffective, and HLA-A11/HLA-A3 CTL (whose lytic 
specificity for melanoma cell lines is restricted by HLA-A11) had no anti- 
tumor effects in vivo or in vitro against the HLA-A2 allogeneic melanoma cell 
line . 
Transfection of B7 to increase the immunogenicity of the immunizing melanoma 
cell line 
B7 is a member of the immunoglobulin gene superfamily (reviewed, 20). It is a 
transmembrane glycoprotein with two immunoglobulin-like extracellular domains 
and a core molecular mass of 30 kd. B7 binds to two antigens on T 
lymphocytes, CD28 and CTLA4, the former which is constitutively expressed on 
95% of CD4+ T cells and 50% of CD8+ T cells, and the latter whose expression 
is induced upon T cell activation. The interaction between B7 on the APC and 
its ligand on the T lymphocyte markedly enhances T cell activation and 
production of IL-2. Under some experimental conditions, antigen presented in 
the absence of a costimulatory signal produced by the B7/CD28 or B7/CTLA4 
interaction induces T cell tolerance. 
Animal models demonstrate an important role for B7 in inducing antitumor 
immunity in vivo. Townsend and Allison transfected a K1735 murine melanoma 
cell line with the murine B7 (21) . In comparison to a control vector- 
transfected K1735 line, the B7 transfected tumor grew poorly in the syngeneic 
host and was able to protect the host from a subsequent challenge by the 
parental tumor cell line. Depletion of the CD8+ T cell subset in vivo 
decreased the immunogenicity of the B7-transfected cell line, and 
restored the growth rate of the tumor to that observed with the parental or a 
vector-transfected control tumor line. Depletion of CD4+ T cells did not 
diminish the immunogenicity of the B7/K1735 tumor cell line, suggesting that 
B7 costimulation provided by the tumor cells may have bypassed the need for 
CD4-mediated T cell help. 
A separate group of investigators conducted similar experiments using the same 
melanoma cell line (22). While they reported that B7 transfection did not 
affect the growth of K1735 in the syngeneic host, tumor size was examined only 
at one early time point (on day 21) . Had the animals been observed for longer 
periods, the experiments in the former study indicate that most of the B7- 
transfected tumors would begin to regress as compared to continued growth of 
the parental cell line. The effect of B7 transfection was more clearly 
Recombinant DNA Research, Volume 18 
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