Primary and Metastatic Uveal Melanoma Cells Genetically Modified to Express HLA–DR and CD80 Present Class II Restricted Tumor Antigens and Activate Tumor–Specific CD4+ T Cells

Abstract

Purpose: : We are developing a cell–based immunotherapy against uveal melanoma metastases. Animal studies and clinical trials indicate that tumor specific CD4⁺ T helper (Th) cells are essential for effective anti–tumor immunity. However, activation of Th cells and identification of Major Histocompatibility Complex Class II (MHC II) restricted tumor antigens is difficult due to the inhibition of Antigen Presenting Cells (APC) within the tumor environment and the failure of MHC II positive tumors to present endogenous tumor antigens. Our studies in mice demonstrate that in the absence of accessory molecule Invariant Chain (Ii), MHC II positive tumor cells present endogenous antigens, stimulate Th cells, and induce protective anti–tumor immunity. Using this strategy for human tumors is difficult, since many tumors express Ii and MHC II when stimulated with IFN–γ. However, melanomas that grow in the immune–privileged environment of the eye do not express MHC II and Ii, even in the presence of exogenous IFN–γ. We hypothesize that Ii negative uveal melanoma cells genetically modified to express MHC II and the co–stimulatory molecule CD80 will present endogenous antigens and activate Th cells.

Methods and Results: : To test this hypothesis we constructed a bicistronic retroviral vector expressing HLA–DRA and HLA–DRB*0101. As measured by flow cytometry, HLA–DRB*0101 and CD80 transduced uveal melanoma cells express HLA–DR1 and CD80 on the cell surface and do not express Ii. To determine if the transduced cells activate CD4+ T cells, HER2/neu–expressing primary and metastatic uveal melanoma transductants MEL202/DR1/CD80 and OMM2.3/DR1/CD80 were co–cultured as stimulator cells with HER2/neu–primed DR1–matched peripheral–blood–mononuclear–cells (PBMC) as responders. The tumor cells activate DR1⁺PBMC as measured by IFN–γ release using ELISA. The responding DR1⁺PBMC are CD4⁺/CD45RO⁺ activated Th cells as measured by flow cytometry.

Conclusions: : Therefore, HLA–DR⁺/CD80⁺ uveal melanoma cells activate Th cells to endogenous antigens, and could be used in uveal melanoma patients to induce tumor–specific CD4⁺ T cells. Supported by NIH CA84232 and EY016486.

Keywords: melanoma • antigen presentation/processing • tumors