Identification of DRG-1 as a melanoma-associated antigen recognized by CD4⁺ Th1 cells

Immunotherapy has emerged as a promising strategy for the treatment of metastatic melanoma. Clinical studies have demonstrated the feasibility of cancer immunotherapy using tumor antigens recognized by CD8⁺ T cells. However, the overall immune responses induced by these antigens are too weak and transient to induce tumor regression in the majority of patients who received immunization. A growing body of evidence suggests that CD4⁺ T helper (Th) cells play an important role in antitumor immunity. Therefore, the identification of MHC class II-restricted tumor antigens capable of stimulating CD4⁺ T cells may provide opportunities for developing effective cancer vaccines. To this end, we describe the identification of developmentally regulated GTP-binding protein 1 (DRG-1) as a melanoma-associated antigen recognized by HLA-DR11-restricted CD4⁺ Th1 cells. Epitope mapping analysis showed that the DRG1_248-268 epitope of DRG-1 was required for T cell recognition. Reverse transcriptionpolymerase chain reaction revealed that DRG-1 was highly expressed in melanoma cell lines but not in normal tissues. DRG-1 knockdown by lentiviral-based shRNA suppressedmelanoma cell proliferation and soft agar colony formation. Taken together, these data suggest that DRG-1 plays an important role inmelanoma cell growth and transformation, indicating that DRG1 may represent a novel target for CD4⁺ T cell-mediated immunotherapy inmelanoma.