CD8A and neoplasm: Analysis of the killing ability of effector CD8+ T cells revealed a dysfunctional phenotype, with a 30% killing efficiency of B16IDO-isolated CD8+ T cells as compared to 54% in B16WT-isolated CD8+ T cells (P = 0.01) and 70% of control in vitro activated tumor antigen-specific CD8+ T cells (pmel1.1), which recognize the melanosomal tumor antigen gp100 (pmel1.1) (P = 0.009) (Fig. 2a).