CD69 and neoplasm: These findings are in agreement with prior reports using TCRαβ-transgenic CD4+ T cells reactive with the melanocyte antigen TRP-1.46,47 The failure of naïve TRP-1-specific CD4+ T cells to reject B16 cells in WT hosts has been interpreted as an inability of B16 cells to prime naïve CD4+ T cells without tumor antigen presentation by host APCs.48 However, when tested in vitro, B16-Ab:env123–139 cells induced CD69 expression in EVα2 T cells reasonably efficiently (Fig. S13), suggesting that they could prime naïve CD4+ T cells under these conditions.