TTK and esophageal squamous cell carcinoma: Moreover, it has shown that these three peptides could stimulate CTLs that recognized and killed ESCC cells endogenously expressing these antigens [7] and that pre-existence of specific T cells, which could respond to the peptides derived from TTK, LY6K, and IMP3, were present in tumor-infiltrating lymphocytes (TIL), regional lymph node lymphocytes (RLNL), and PBLs obtained from HLA-A*2402 positive patients with ESCC [12].