Human Gene Therapy Subcommittee - 11/21-22/91 
Michigan. Dr. Epstein stated that the objective of the protocol was to modify or 
enhance the immunologic response to tumors by antigenic modification. There is a 
question if there were enough experimental animal data to justify this protocol since the 
investigators observed positive results in only two mice. This protocol is designed to 
introduce a gene encoding for a class I histocompatibility antigen in tumor cells. The 
rationale for this approach is that data from model systems demonstrate that the 
introduction of a foreign class I antigen into tumor cells elicits an immune response 
against that antigen as well as other non-class I antigens on the tumor cells. Therefore, 
the foreign antigen serves to stimulate an immune response against all of the patient's 
tumor cells. 
Dr. Epstein explained that the histocompatibility antigen gene being used in this protocol 
codes for HLA-B7. This gene has been cloned into three vectors that have been inserted 
into liposomes in order to facilitate their introduction into cells. These liposomes will be 
injected directly into tumor nodules in an escalating dose schedule. In this proposed 
Phase I trial, the investigators will monitor patients for side effects, immune response, 
evidence of autoimmune reactions, and the effects on existing tumor. 
Dr. Epstein described the first vector, Vector I, as a derivative of the retroviral vector, 
PLJ, which is derived from the Moloney murine leukemia virus. In response to concerns 
raised at the July 29-30, 1991, HGTS meeting, the investigators have replaced the 3' long 
terminal repeat (LTR) and the polyoma virus early region with the 3' untranslated and 
polyadenylation sequences of the SV40 early region. Therefore, the polyoma virus 
sequences that could pose potential risk to the patient have been eliminated. 
The new vector, Vector II, has the HLA-B7 gene inserted into a P-globin expression 
vector. In this vector, the p-globin gene has been removed, and the Rous sarcoma virus 
(RSV) enhancer, the 3' untranslated, and polyadenylation sequences of the SV40 early 
region have been inserted. 
Vector III incorporates the 3' untranslated, and polyadenylation sequences of the rabbit 
p-globin gene. The differences between this revised protocol and the original protocol 
presented at the last HGTS meeting is that Dr. Nabel has modified the original vector 
and developed two additional expression vectors. 
Dr. Epstein reviewed the preliminary animal data involving a mouse model system. 
Tumors were established using the CT26 colon adenocarcinoma line transduced with the 
original PLJ vector containing the gene for H-2K S . One percent of these tumor cells 
were effectively transduced and exhibited gene expression. Cytotoxic T lymphocytes 
(CTL) were generated. This observation was confirmed by data demonstrating that 
antibodies against the CTL marker abrogated this response. 
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