The increasing application of active specific immunotherapy for the treatment of malignant diseases has highlighted two major challenges in tumor immunology: i) overcoming unresponsiveness and eliciting a strong immune response to tumor associated antigens (TAA) since most of the TAA expressed by human tumor cells are non-mutated self-antigens, and ii) designing effective strategies to counteract the multiple mechanisms utilized by tumor cells to escape from immune recognition and destruction since they have a negative impact on the outcome of immunotherapy. The strategies to be developed and tested in this proposal stem from the results of a trial in patients with melanoma with the anti-idiotypic (anti-id) mAb MK2-23. The latter mimics the human high molecular weight-melanoma associated antigen (HMW-MAA), which is a cell surface, membrane bound self-antigen. At variance with HMW-MAA, the anti-id mAb MK2-23 broke tolerance to selfHMW-MAA in about 60 percent of patients with melanoma. The level of anti-HMW-MAA antibodies in the immunized patients was low. Furthermore, the ability of anti-id mAb to elicit a HMW-MAA specific CTL response is questionable. To overcome these limitations, this proposal aims at testing the hypotheses that i) unresponsiveness to HMW-MAA can be overcome by immunizations with a DNA minigene encoding peptide mimetics of HMW-MAA B cell epitopes, and the weak anti-HMW-MAA immune response can be markedly enhanced by booster(s) with a DNA plasmid encoding intact HMW-MAA. ii) HLA class I restricted, HMW-MAA specific CTL can be induced by a DNA minigene encoding CTL defined epitopes of HMW-MAA. HMW-MAA has been selected for our investigations since this cell surface membrane-bound antigen has been successfully used for immunotherapy of melanoma, and HMW-MAA mimetics have already been identified in our laboratory. DNA minigenes will be utilized as immunogens as they are highly immunogenic, can be easily produced at low cost, and are easily handled. The information derived from the outlined studies will contribute to develop novel strategies to implement active specific immunotherapy of malignant diseases.
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