CD8A and neoplasm: The drawback of this strategy comes from numerous factors: (i) a limited number of known synthesized short peptides cannot be available in many HLA molecules [51–53], (ii) CD8+ CTLs may be ineffective in reacting with pancreatic cancer cells downregulated by certain tumor antigens and MHC class I molecules, which may appear during the course of tumor progression [22], (iii) impaired function of APCs in patients with advanced pancreatic cancer [54, 55], and (iv) MDSCs or Treg cells in tumor environment produce immunosuppressive cytokines such as IL-10 and TGF-β [26].