cells with high efficacy would theoretically be far superior to currently available therapies. 
The goal of immunotherapy is to stimulate the immune system to recognize and kill cancer 
cells by modifying the tumor cells or modifying the host response by such mechanisms as 
expanding the lymphocytes that respond specifically to the antigens on the tumor cells. 
Immunotherapy has shown promise as an approach to the treatment of malignancy. 
Indeed, cancers such as melanoma, renal cell carcinoma ^d colon adenocarcinoma are 
responsive to modulation of immune function, because the immune system can be induced 
to recognize tumor associated and tumor specific antigens in these cells. 
Over the last several decades, there have been many attempts to identify tumor-specific 
antigens that might be the targets for cytotoxic antibodies or cell-mediated immunity. There 
have been numerous attempts to develop vaccines and monoclonal antibodies directed at 
one or more preferentially expressed cell surface antigens in a variety of cancers. Overall, 
tumor vaccines using intact cells or extracts plus adjuvants have given about a 10-20% 
response rate. Other approaches to immunotherapy have involved the administration of 
non-specific immunomodulating agents such as Bacillus Calmette-Guerin (BCG), cytokines, 
and/or adoptive transfer of cytotoxic T cells (CTL’s), which have shown promise in animal 
models (1-6) and in man (7-10). More recently, molecular genetic interventions have been 
designed in an attempt to improve the efficacy of immunotherapy. 
Nabel and colleagues at the University of Michigan are investigating a novel molecular 
genetic intervention for human malignancy that enhances the immune response to tumors 
by in vivo gene transfer. This immunotherapeutic approach based on animal model work 
(11, 12) uses a gene encoding a transplantation antigen, an allogeneic class I major 
histocompatibility complex (MHC) antigen, HLA-B7, introduced into human tumors in 
vivo by DNA/lipid complex transfection. The direct intratumoral injection approach is 
used. Expression of allogeneic MHC antigens on tumor cells stimulates immunity against 
both the transfected cells as well as previously unrecognized antigens present in 
unmodified tumor cells. The introduction of an allogeneic MHC gene directly into tumors 
in vivo has induced partial tumor regressions, as well as specific cytotoxic T cell responses 
to other antigens. 
In a preliminary trial in humans with malignant melanoma Nabel treated 5 patients with 
malignant melanoma. Three patients received 3 treatments, totaling 0.87 pg of DNA 
intratumorally, and 3 patients (2 additional patients plus one of the original 3 patients) 
received cumulative dose of 2.58 pg of DNA via three treatments. No toxicity resulted 
from this form of treatment and there was no formation of anti DNA antibody or 
autoantibody. There was no plasmid DNA detectable in the blood by PCR following gene 
transfer (tested on days 3-7 post transfection at ~2 pg/ml sensitivity). 
Evidence of gene transfer was found on biopsy of the injected tumor. The biopsy samples 
were analyzed for plasmid DNA, mRNA coding for HLA-B7 and the expression of HLA-B7 
protein. In 4 of the 5 patients, plasmid DNA and HLA-B7 mRNA were detected within the 
treated nodules by PCR. HLA-B7 expression was confirmed in all treated nodules by 
immunohistochemical staining with a monoclonal antibody to the gene product. Two 
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Recombinant DNA Research, Volume 19 
