IMMUNIZATION AGAINST GD3 USING ANTIIDIOTYPIC MAB BEC2

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The long term goal of this project is to develop a vaccine against GD3 ganglioside in order to test the hypothesis that induction of an active immune response against GD3 ganglioside will improve the survival of melanoma patients. GD3 was selected as a target for immunotherapy because: a) it is abundantly expressed on virtually all melanoma but is expressed on few normal tissues and at much lower levels, b) it is involved in critical cell functions, and c) passive immunotherapy trials with monoclonal antibodies (MAb) against GD3 have resulted in major clinical responses in patients with melanoma. Previous immunization trials using GD3+ cell lines, purified GD3, or GD3 conjugates have failed to induce antibodies against GD3 in melanoma patients suggesting that GD3 is poorly immunogenic. In an attempt to overcome this poor immunogenicity, we developed a murine anti-idiotypic MAb, designated BEC2, that mimics GD3 and can induce anti-GD3 IgG in rabbits. Thus, we are using a xenogeneic protein (BEC2) to mimic a poorly-immunogenic glycolipid (GD3). Previous clinical trials carried out with BEC2, in which only a minority of patients immunized developed anti-GD3 antibodies, demonstrated that a) an adjuvant is necessary to induce anti-GD3 antibodies and that BCG was the best adjuvant tested, and b) intravenous (IV) administration was more immunogenic than the subcutaneous or intramuscular routes and a dose of 10 mg IV was needed to induce anti-GD3 antibodies. We are also aware of results using other vaccines that demonstrate that conjugation of poorly-immunogenic antigens to carrier proteins such as keyhole limpet hemocyanin (KLH) greatly enhances the immune response induced. The work proposed in this application incorporates what has been learned from previous trials and is designed to increase significantly the percentage of patients who develop anti-GD3 responses after immunization with BEC2. The proposed clinical trial tests two hypotheses. Hypothesis # l: Immunization with BEC2 conjugated to KLH and administered with BCG (BEC2-KLH + BCG) will induce an anti-GD3 humoral response in a majority of melanoma patients. Hypothesis #2: After initial immunization, IV administration of 10 mg of BEC2 will boost the anti-GD3 humoral response. To test the first hypothesis, patients who have undergone complete surgical excision of melanoma but who are at high risk for recurrence will receive 5 intradermal immunizations with BEC2-KLH + BCG. Serum will be collected before each immunization and 2 weeks following each immunization. Anti-GD3 antibodies will be assayed using an ELISA that has been carefully developed for sensitivity and reproducibility, and criteria have been established in our lab to distinguish significant rises in anti-GD3 reactivity from normal intra-patient variability. Sera that show increased anti-GD3 reactivity will be further studied for binding specificity. To test the second hypothesis, the patients will receive a series of 3 booster immunizations of 10 mg of BEC2 administered IV every three months starting 12 weeks after the 5th injection of BEC2-KLH + BCG. Serum collected before and 2 weeks after each booster will be analyzed as previously described. A 4-fold or greater increase in anti-GD3 titer over pre-booster titers will be considered evidence of a booster effect and the percentage of patients demonstrating a booster effect will be noted.