Our anti-Id antibody, 1A7 mimicking GD2, induced both Ab3 and Ab1' humoral responses in injected small animals (54), primates (38), as well as melanoma patients (55). However, presumed cellular responses could not be detected in the injected patients. Various plasmid constructs have been reported to invoke combined humoral and cellular immune responses in injected hosts against the transgene product. To investigate the induction of cellular immune responses we constructed two plasmids expressing 1A7 scFv for use as vaccines. One of the plasmids expressed the VH-Ln-VL format of scFv, whereas the other expressed the VL-Ln-VH format (56). Following intramuscular injection of mice, the plasmids were detectable in the injected tissues for at least 3 mo and the injected plasmids actively transcribed the scFv of 1A7 at the injected site. A single intramuscular immunization of mice with either of the plasmids in phosphate-buffered saline induced humoral immune responses against 1A7 as well as GD2. Multiple immunizations, however, were required to elicit stronger humoral responses. No cellular responses were invoked by immunization with the plasmids (56). Thus, for anti-Id antibody therapy, the DNA vaccines do not appear to be better than the protein vaccines.
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