IDENTIFICATION OF SUBDOMINANT CTL EPITOPES OF THE GP100 MELANOMA-ASSOCIATED TUMOR-ANTIGEN BY PRIMARY IN-VITRO IMMUNIZATION WITH PEPTIDE-PULSED DENDRITIC CELLS

The gp100 melanoma-associated tumor Ag was selected as a model system to study the diversity of human antitumor cytotoxic T cell responses. First, peptides corresponding to dominant gp100 HLA-A2.1-restricted CT L epitopes were tested using lymphocytes from normal volunteers and an in vitro priming protocol that uses peptide-pulsed dendritic cells as APCs and IL-7 and IL-10 as immune-enhancing cytokines. High CTL activ ity toward both peptide-pulsed target cells and gp100(+) melanoma cell s was obtained with four out of five peptides tested. Second, HLA-A2.1 -binding peptides from gp100 that do not appear to represent CTL epito pes in melanoma patients were also tested for their capacity to induce CTL using the in vitro priming protocol, Three of six peptides tested induced CTL in lymphocytes from normal volunteers. One of these pepti des was also immunogenic for lymphocytes derived from a melanoma patie nt in remission, Because these three CTL epitopes were not recognized in the natural immune response in melanoma patients but do appear as i mmunogens when peptides are used to induce the T cell response, they m ay be considered as typical ''subdominant'' epitopes. The results are discussed in the context of the usefulness of this approach to detail the immunologic potential of a given tumor-associated Ag and its relev ance for the design of effective immune-based therapies.