Identification of multiple HLA-DR-restricted epitopes of the tumor-associated antigen CAMEL by CD4+ Th1/Th2 lymphocytes

CD4(+) Th cells play an important role in the induction and maintenance of adequate CD8(+) T cell-mediated antitumor responses. Therefore, identification of MHC class II-restricted tumor antigenic epitopes is of major importance for the development of effective immunotherapies with synthetic peptides. CAMEL and NY-ESO-ORF2 are tumor Ags translated in an alternative open reading frame from the highly homologous LAGE-1 and NY-ESO-1 genes, respectively. In this study, we investigated whether CD4(+) T cell responses could be induced in vitro by autologous, mature dendritic cells pulsed with recombinant CAMEL protein. The data show efficient induction of CAMEL-specific CD4(+) T cells with mixed Th1/Th2 phenotype in two healthy donors. Isolation of CD4(+) T cell clones from the T cell cultures of both donors led to the identification of four naturally processed HLA-DR-binding CAMEL epitopes: CAMEL(1-20), CAMEL(14-33), CAMEL(46-65), and CAMEL(81-102). Two peptides (CAMEL(1-20) and CAMEL(14-33)) also contain previously identified HLA class I-binding CD8(+) T cell epitopes shared by CAMEL and NY-ESO-ORF2 and are therefore interesting tools to explore for immunotherapy. Furthermore, two CD4(+) T cell clones that recognized the CAMEL(14-33) peptide with similar affinities were shown to differ in recognition of tumor cells. These CD4(+) T cell clones recognized the same minimal epitope and expressed similar levels of adhesion, costimulatory, and inhibitory molecules. TCR analysis demonstrated that these clones expressed identical TCR beta-chains, but different complementarity-determining region 3 loops of the TCR alpha-chains. Introduction of the TCRs into proper recipient cells should reveal whether the different complementarity-determining region 3 alpha loops are important for tumor cell recognition.