Retrovirally transduced human dendritic cells can generate T cells recognizing multiple MHC class I and class II epitopes from the melanoma antigen glycoprotein 100

Involvement of tumor-Ag specific CD4⁺ and CD8⁺ T cells could be critical in the generation of an effective immunotherapy for cancer. In an attempt to optimize the T cell response against defined tumor Ags, we previously developed a method allowing transgene expression in human dendritic cells (DCs) using retroviral vectors. One advantage of using gene-modified DCs is the potential ability to generate CD8⁺ T cells against multiple class I-restricted epitopes within the Ag, thereby eliciting a broad antitumor immune response. To test this, we generated tumor-reactive CD8⁺ T cells with DCs transduced with the melanoma Ag gp100, for which a number of HLA-A2-restricted epitopes have been described. Using gp100-transduced DCs, we were indeed able to raise T cells recognizing three distinct HLA-A2 epitopes within the Ag, gp100_154-162, gp100_209-217, and gp100_280-288. We next tested the ability of transduced DCs to raise class II-restricted CD4⁺ T cells. Interestingly, stimulation with gp100-transduced DCs resulted in the generation of CD4⁺ T cells specific for a novel HLA-DRβ1*0701-restricted epitope of gp100. The minimal determinant of this epitope was defined as gp100_174-190 (TGRAMLGTHTMEVTVYH). These observations suggest that retrovirally transduced DCs have the capacity to present multiple MHC class I- and class II-restricted peptides derived from a tumor Ag, thereby eliciting a robust immune response against that Ag.