ARTICLE ABSTRACTPurpose: To identify long peptides (LP) derived from a novel tumor-associated antigen (TAA), kinesin family member 20A (KIF20A), which induce tumor-specific T-helper type 1 (TH1) cells and CTLs.Experimental Design: We combined information from a recently developed computer algorithm predicting HLA class II–binding peptides with KIF20A-derived CTL-epitope sequences presented by HLA-A2 (A*02:01) or HLA-A24 (A*24:02) to select candidate promiscuous TH1-cell epitopes containing CTL epitopes. Peripheral blood mononuclear cells (PBMC) derived from healthy donors or patients with head-and-neck malignant tumor (HNMT) were used to study the immunogenicity of KIF20A-LPs, and the in vitro cross-priming potential of KIF20A-LPs bearing CTL epitopes. We used HLA-A24 transgenic mice to address whether vaccination with KIF20A-LP induces efficient cross-priming of CTLs in vivo. The TH1-cell response to KIF20A-LPs in HNMT patients receiving immunotherapy with TAA-derived CTL-epitope peptides was analyzed using IFN-γ enzyme-linked immunospot assays.Results: We identified promiscuous KIF20A-LPs bearing naturally processed epitopes recognized by CD4+ T cells and CTLs. KIF20A-specific CTLs were induced by vaccination with a KIF20A-LP in vivo. KIF20A expression was detected in 55% of HNMT by immunohistochemistry, and significant frequencies of KIF20A-specific TH1 cell responses were detected after short-term in vitro stimulation of PBMCs with KIF20A-LPs in 50% of HNMT patients, but not in healthy donors. Furthermore, these responses were associated with KIF20A expression in HNMT tissues.Conclusions: These are the first results showing the presence of KIF20A-specific TH1 cell responses in HNMT patients and underline the possible utility of KIF20A-LPs for propagation of TH1 cells and CTLs. Clin Cancer Res; 19(16); 4508–20. ©2013 AACR.