The ganglioside GD2 is the target of several monoclonal antibody (MAb) trials that have shown therapeutic effects in melanoma and neuroblastoma patients. In addition, GD2 is a potential target for the treatment of gliomas, retinoblastomas, sarcomas and small cell lung carcinomas that all express the antigen. Active immunotherapy against GD2 may be advantageous over passive immunotherapy with MAbs by inducing sustained immunity. However, GD2 is difficult to purify in amounts sufficient for immunizations, weakly immunogenic when presented by the growing tumor or in a vaccine and often elicits a short-lived IgM response of poor memory without inducing a T-cell response. In contrast, anti-idiotypic antibodies (Ab2) mimicking GD2 are easily produced in large quantities, and have induced GD2-specific IgG, proliferative lymphocyte and CD4-dependent delayed-type hypersensitivity (DTH) responses in animals. The major goals of the proposed studies are to compare the immunogenicity and protective activity of GD2 and Ab2, and to elucidate the mechanism of GD2 mimicry by Ab2. This information will be utilized to induce maximal humoral, cellular and tumor-protective immunity directed against GD2. This project includes the following aims: (1) Test the hypothesis that humoral, cellular and tumor-protective immunity induced by anti-idiotype TA412G mimicking GD2 differs qualitatively and quantitatively from the immunity induced by the antigen. Polyclonal and MAbs induced by Ab2 or antigen will be evaluated for specificity, isotype, cytotoxic activity against tumor cells, avidity, kinetics, and V region sequences (MAb only). Induced cellular immunity will be evaluated for in vitro proliferative lymphocytes, in vivo hypersensitive lymphocytes of the delayed type, and in vitro cytolytic lymphocytes. Tumor-protective responses will be evaluated for epitope spreading in vivo and induction of immunological memory. (2) Determine the molecular and structural basis for GD2 mimicry by Ab2. Selected peptides derived from the VH and VL of GD2-mimicking Ab2 or from peptide phage libraries will be evaluated for their capacity to induce humoral, cellular and/or protective immunity to GD2. The structural basis for GD2 mimicry by Ab2 or peptide will be determined. The proposed studies will provide important information on the comparative immunogenicity and tumor-protective activity of gangliosides and their Ab2/peptide mimics. Elucidation of the mechanism of and structural basis for carbohydrate mimicry by proteins and peptides will impact not only on cancer vaccine development, but also on therapies against viral, bacterial, parasitic and autoimmune diseases.