HLA-A2-restricted CTLs, which lysed high molecular weight (HMW)-melanoma-associated antigen (MAA)(+) melanoma cells, were induced in patients with melanoma immunized with MELIMMUNE, a combination of the murine anti-idiotypic (anti-id) monoclonal antibodies (mAb) MEL-2 and MF11-30 (MW Pride et al., Clin Cancer Res 1998;4:2363.). In the present study we investigated whether CTL epitopes are present in anti-id mAb MF-11-30 and activate T cells to recognize HMW-MAA on melanoma cells. One candidate epitope in the mAb MF11-30 VH chain, VH (3-11), was selected based on the presence of HLA-A2 anchor residues and partial homology with the HMW-MAA epitope, HMW-MAA (76-84). Lymphocytes from HLA-A2(+)-immunized patients proliferated to VH (3-11) peptide and to a variant HMW-MAA peptide to a significantly greater extent than autologous lymphocytes stimulated with an irrelevant peptide and lymphocytes from nonimmunized patients. No proliferative response was detected to the wild-type HMW-MAA peptide (76-84). Significant increase in IFN-gamma production but not in interleukin 10 production in response to VH (3-11) and to variant HMW-MAA peptide (76-84) was observed in lymphocytes from the immunized patients. Stimulation of lymphocytes from HLA-A2(+) patients with the two peptides induced CTL, which lysed HMW-MAA(+)/HLA-A2(+) A375SM melanoma cells. This is the first report documenting the presence of immunogenic peptides in a murine anti-id mAb for a defined epitope expressed by a human melanoma-associated antigen. These results may be relevant for development of novel vaccines based on homology between anti-id mAb and tumor-associated antigen amino acid sequences.